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He Q, Chaillet JK, Labbé F. Antigenic strain diversity predicts different biogeographic patterns of maintenance and decline of antimalarial drug resistance. eLife 2024; 12:RP90888. [PMID: 38363295 PMCID: PMC10942604 DOI: 10.7554/elife.90888] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/17/2024] Open
Abstract
The establishment and spread of antimalarial drug resistance vary drastically across different biogeographic regions. Though most infections occur in sub-Saharan Africa, resistant strains often emerge in low-transmission regions. Existing models on resistance evolution lack consensus on the relationship between transmission intensity and drug resistance, possibly due to overlooking the feedback between antigenic diversity, host immunity, and selection for resistance. To address this, we developed a novel compartmental model that tracks sensitive and resistant parasite strains, as well as the host dynamics of generalized and antigen-specific immunity. Our results show a negative correlation between parasite prevalence and resistance frequency, regardless of resistance cost or efficacy. Validation using chloroquine-resistant marker data supports this trend. Post discontinuation of drugs, resistance remains high in low-diversity, low-transmission regions, while it steadily decreases in high-diversity, high-transmission regions. Our study underscores the critical role of malaria strain diversity in the biogeographic patterns of resistance evolution.
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Affiliation(s)
- Qixin He
- Department of Biological Sciences, Purdue UniversityWest LafayetteUnited States
| | - John K Chaillet
- Department of Biological Sciences, Purdue UniversityWest LafayetteUnited States
| | - Frédéric Labbé
- Department of Ecology and Evolution, University of ChicagoChicagoUnited States
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2
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He Q, Chaillet JK, Labbé F. Antigenic strain diversity predicts different biogeographic patterns of maintenance and decline of anti-malarial drug resistance. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.03.06.531320. [PMID: 37987011 PMCID: PMC10659383 DOI: 10.1101/2023.03.06.531320] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2023]
Abstract
The establishment and spread of anti-malarial drug resistance vary drastically across different biogeographic regions. Though most infections occur in Sub-Saharan Africa, resistant strains often emerge in low-transmission regions. Existing models on resistance evolution lack consensus on the relationship between transmission intensity and drug resistance, possibly due to overlooking the feedback between antigenic diversity, host immunity, and selection for resistance. To address this, we developed a novel compartmental model that tracks sensitive and resistant parasite strains, as well as the host dynamics of generalized and antigen-specific immunity. Our results show a negative correlation between parasite prevalence and resistance frequency, regardless of resistance cost or efficacy. Validation using chloroquine-resistant marker data supports this trend. Post discontinuation of drugs, resistance remains high in low-diversity, low-transmission regions, while it steadily decreases in high-diversity, high-transmission regions. Our study underscores the critical role of malaria strain diversity in the biogeographic patterns of resistance evolution.
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Affiliation(s)
- Qixin He
- Department of Biological Sciences, Purdue University, West Lafayette, IN, USA
| | - John K. Chaillet
- Department of Biological Sciences, Purdue University, West Lafayette, IN, USA
| | - Frédéric Labbé
- Department of Ecology and Evolution, University of Chicago, Chicago, IL, USA
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Dieng CC, Morrison V, Donu D, Cui L, Amoah L, Afrane Y, Lo E. Distribution of Plasmodium falciparum K13 gene polymorphisms across transmission settings in Ghana. BMC Infect Dis 2023; 23:801. [PMID: 37974079 PMCID: PMC10652499 DOI: 10.1186/s12879-023-08812-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2022] [Accepted: 11/12/2023] [Indexed: 11/19/2023] Open
Abstract
Malaria is a significant global health concern, with a majority of cases in Sub-Saharan African nations. Numerous antimalarial drugs have been developed to counter the rampant prevalence of Plasmodium falciparum malaria. Artemisinin-based Combination Therapy (ACT) has served as the primary treatment of uncomplicated malaria in Ghana since 2005. However, a growing concern has emerged due to the escalating reports of ACT resistance, particularly in Southeast Asia, and its encroachment into Africa. Specifically, mutations in the Kelch propeller domain on chromosome 13 (Pfk13) have been linked to ACT resistance. Yet, our understanding of mutation prevalence in Africa remains largely uncharted. In this study, we compared Pfk13 sequences obtained from 172 P. falciparum samples across three ecological and transmission zones in Ghana. We identified 27 non-synonymous mutations among these sequences, of which two of the mutations, C580Y (found in two samples from the central region) and Y493H (found in one sample from the north), had previously been validated for their association with artemisinin resistance, a phenomenon widespread in Southeast Asia. The Pfk13 gene diversity was most pronounced in the northern savannah than the central forest and south coastal regions, where transmission rates are lower. The observed mutations were not significantly associated with geographical regions, suggesting a frequent spread of mutations across the country. The ongoing global surveillance of artemisinin resistance remains pivotal, and our findings provides insights into the potential spread of resistant parasites in West Africa. Furthermore, the identification of novel codon mutations in this study raises their potential association to ACT resistance, warranting further investigation through in vitro assays to ascertain their functional significance.
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Affiliation(s)
- Cheikh Cambel Dieng
- Department of Microbiology and Immunology, College of Medicine, Drexel University, Philadelphia, PA, USA.
| | - Victoria Morrison
- Department of Biological Sciences, University of North Carolina at Charlotte, Charlotte, NC, USA
| | - Dickson Donu
- Department of Immunology, Noguchi Memorial Institute for Medical Research, University of Ghana, Accra, Ghana
| | - Liwang Cui
- Morsani College of Medicine, University of South Florida, Tampa, FL, USA
| | - Linda Amoah
- Department of Immunology, Noguchi Memorial Institute for Medical Research, University of Ghana, Accra, Ghana
- West Africa Center for Cell Biology of Infectious Pathogens, University of Ghana, Accra, Ghana
| | - Yaw Afrane
- Department of Microbiology, University of Ghana Medical School, University of Ghana, Accra, Ghana
| | - Eugenia Lo
- Department of Microbiology and Immunology, College of Medicine, Drexel University, Philadelphia, PA, USA.
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Moss S, Mańko E, Vasileva H, Da Silva ET, Goncalves A, Osborne A, Phelan J, Rodrigues A, Djata P, D'Alessandro U, Mabey D, Krishna S, Last A, Clark TG, Campino S. Population dynamics and drug resistance mutations in Plasmodium falciparum on the Bijagós Archipelago, Guinea-Bissau. Sci Rep 2023; 13:6311. [PMID: 37072433 PMCID: PMC10113324 DOI: 10.1038/s41598-023-33176-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2022] [Accepted: 04/08/2023] [Indexed: 05/03/2023] Open
Abstract
Following integrated malaria control interventions, malaria burden on the Bijagós Archipelago has significantly decreased. Understanding the genomic diversity of circulating Plasmodium falciparum malaria parasites can assist infection control, through identifying drug resistance mutations and characterising the complexity of population structure. This study presents the first whole genome sequence data for P. falciparum isolates from the Bijagós Archipelago. Amplified DNA from P. falciparum isolates sourced from dried blood spot samples of 15 asymptomatic malaria cases were sequenced. Using 1.3 million SNPs characterised across 795 African P. falciparum isolates, population structure analyses revealed that isolates from the archipelago cluster with samples from mainland West Africa and appear closely related to mainland populations; without forming a separate phylogenetic cluster. This study characterises SNPs associated with antimalarial drug resistance on the archipelago. We observed fixation of the PfDHFR mutations N51I and S108N, associated with resistance to sulphadoxine-pyrimethamine, and the continued presence of PfCRT K76T, associated with chloroquine resistance. These data have relevance for infection control and drug resistance surveillance; particularly considering expected increases in antimalarial drug use following updated WHO recommendations, and the recent implementation of seasonal malaria chemoprevention and mass drug administration in the region.
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Affiliation(s)
- Sophie Moss
- Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, UK.
| | - Emilia Mańko
- Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, UK
| | - Hristina Vasileva
- Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, UK
| | - Eunice Teixeira Da Silva
- Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, UK
- Ministry of Public Health, Bissau, Guinea-Bissau
| | - Adriana Goncalves
- Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, UK
| | - Ashley Osborne
- Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, UK
| | - Jody Phelan
- Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, UK
| | | | - Paulo Djata
- National Malaria Control Programme, Ministry of Public Health, Bissau, Guinea-Bissau
| | | | - David Mabey
- Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, UK
| | - Sanjeev Krishna
- Clinical Academic Group, Institute for Infection and Immunity, and St. George's University Hospitals NHS Foundation Trust, St. George's University of London, London, UK
- Centre de Recherches Médicales de Lambaréné (CERMEL), Lambaréné, Gabon
- Institut Für Tropenmedizin Universitätsklinikum Tübingen, Tübingen, Germany
| | - Anna Last
- Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, UK
| | - Taane G Clark
- Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, UK
- Faculty of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, London, UK
| | - Susana Campino
- Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, UK.
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Egwu CO, Aloke C, Chukwu J, Agwu A, Alum E, Tsamesidis I, Aja PM, Offor CE, Obasi NA. A world free of malaria: It is time for Africa to actively champion and take leadership of elimination and eradication strategies. Afr Health Sci 2022; 22:627-640. [PMID: 37092107 PMCID: PMC10117514 DOI: 10.4314/ahs.v22i4.68] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/06/2023] Open
Abstract
The global burden of malaria seems unabated. Africa carries the greatest burden accounting for over 95% of the annual cases of malaria. For the vision of a world free of malaria by Global Technical Strategy to be achieved, Africa must take up the stakeholder's role. It is therefore imperative that Africa rises up to the challenge of malaria and champion the fight against it. The fight against malaria may just be a futile or mere academic venture if Africans are not directly and fully involved. This work reviews the roles playable by Africans in order to curb the malaria in Africa and the world at large.
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Affiliation(s)
- Chinedu Ogbonnia Egwu
- Medical Biochemistry Department, College of Medicine, Alex-Ekwueme Federal University Ndufu-Alike Ikwo, P.M.B. 1010 Ebonyi State, Nigeria
| | - Chinyere Aloke
- Medical Biochemistry Department, College of Medicine, Alex-Ekwueme Federal University Ndufu-Alike Ikwo, P.M.B. 1010 Ebonyi State, Nigeria
- Protein Structure-Function and Research Unit, School of Molecular and Cell Biology, Faculty of Science, University of the Witwatersrand, Braamfontein, Johannesburg 2050, South Africa
| | - Jennifer Chukwu
- World Health Organization, United Nations House Plot 617/618 Central Area District PMB 2861 Abuja, Nigeria
| | - Anthony Agwu
- Biochemistry Department, Ebonyi State University Abakaliki, P.M.B. 053 Ebonyi State Nigeria
| | - Esther Alum
- Biochemistry Department, Ebonyi State University Abakaliki, P.M.B. 053 Ebonyi State Nigeria
| | - Ioannis Tsamesidis
- Department of Prosthodontics, School of Dentistry, Faculty of Health Sciences, Aristotle University of Thessaloniki 54124 Greece
| | - Patrick M Aja
- Biochemistry Department, Ebonyi State University Abakaliki, P.M.B. 053 Ebonyi State Nigeria
| | - Christian E Offor
- Biochemistry Department, Ebonyi State University Abakaliki, P.M.B. 053 Ebonyi State Nigeria
| | - Nwogo Ajuka Obasi
- Medical Biochemistry Department, College of Medicine, Alex-Ekwueme Federal University Ndufu-Alike Ikwo, P.M.B. 1010 Ebonyi State, Nigeria
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The Rare, the Best: Spread of Antimalarial-Resistant Plasmodium falciparum Parasites by Anopheles Mosquito Vectors. Microbiol Spectr 2021; 9:e0085221. [PMID: 34668767 PMCID: PMC8528099 DOI: 10.1128/spectrum.00852-21] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
The emergence of resistance to antimalarials has prompted the steady switch to novel therapies for decades. Withdrawal of antimalarials, such as chloroquine in sub-Saharan Africa in the late 1990s, led to rapid declines in the prevalence of resistance markers after a few years, raising the possibility of reintroducing them for malaria treatment. Here, we provide evidence that the mosquito vector plays a crucial role in maintaining parasite genetic diversity. We followed the transmission dynamics of Plasmodium falciparum parasites through its vector in natural infections from gametocytes contained in the blood of asymptomatic volunteers until sporozoites subsequently developed in the mosquito salivary glands. We did not find any selection of the mutant or wild-type pfcrt 76 allele during development in the Anopheles mosquito vector. However, microsatellite genotyping indicated that minority genotypes were favored during transmission through the mosquito. The analysis of changes in the proportions of mutant and wild-type pfcrt 76 alleles showed that, regardless of the genotype, the less-represented allele in the gametocyte population was more abundant in mosquito salivary glands, indicating a selective advantage of the minority allele in the vector. Selection of minority genotypes in the vector would explain the persistence of drug-resistant alleles in the absence of drug pressure in areas with high malaria endemicity and high genetic diversity. Our results may have important epidemiological implications, as they predict the rapid re-emergence and spread of resistant genotypes if antimalarials that had previously selected resistant parasites are reintroduced for malaria prevention or treatment. IMPORTANCE Drug selection pressure in malaria patients is the cause of the emergence of resistant parasites. Resistance imposes a fitness cost for parasites in untreated infections, so withdrawal of the drug leads to the return of susceptible parasites. Little is known about the role of the malaria vector in this phenomenon. In an experimental study conducted in Cameroon, an area of high malaria transmission, we showed that the vector did not favor the parasites based on sensitivity or resistance criteria, but it did favor the selection of minority clones. This finding shows that the vector increases the diversity of plasmodial populations and could play an important role in falciparum malaria epidemiology by maintaining resistant clones despite the absence of therapeutic pressure.
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Whitlock AOB, Juliano JJ, Mideo N. Immune selection suppresses the emergence of drug resistance in malaria parasites but facilitates its spread. PLoS Comput Biol 2021; 17:e1008577. [PMID: 34280179 PMCID: PMC8321109 DOI: 10.1371/journal.pcbi.1008577] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2020] [Revised: 07/29/2021] [Accepted: 06/04/2021] [Indexed: 12/23/2022] Open
Abstract
Although drug resistance in Plasmodium falciparum typically evolves in regions of low transmission, resistance spreads readily following introduction to regions with a heavier disease burden. This suggests that the origin and the spread of resistance are governed by different processes, and that high transmission intensity specifically impedes the origin. Factors associated with high transmission, such as highly immune hosts and competition within genetically diverse infections, are associated with suppression of resistant lineages within hosts. However, interactions between these factors have rarely been investigated and the specific relationship between adaptive immunity and selection for resistance has not been explored. Here, we developed a multiscale, agent-based model of Plasmodium parasites, hosts, and vectors to examine how host and parasite dynamics shape the evolution of resistance in populations with different transmission intensities. We found that selection for antigenic novelty (“immune selection”) suppressed the evolution of resistance in high transmission settings. We show that high levels of population immunity increased the strength of immune selection relative to selection for resistance. As a result, immune selection delayed the evolution of resistance in high transmission populations by allowing novel, sensitive lineages to remain in circulation at the expense of the spread of a resistant lineage. In contrast, in low transmission settings, we observed that resistant strains were able to sweep to high population prevalence without interference. Additionally, we found that the relationship between immune selection and resistance changed when resistance was widespread. Once resistance was common enough to be found on many antigenic backgrounds, immune selection stably maintained resistant parasites in the population by allowing them to proliferate, even in untreated hosts, when resistance was linked to a novel epitope. Our results suggest that immune selection plays a role in the global pattern of resistance evolution. Drug resistance in the malaria parasite, Plasmodium falciparum, presents an ongoing public health challenge, but aspects of its evolution are poorly understood. Although antimalarial resistance is common worldwide, it can typically be traced to just a handful of evolutionary origins. Counterintuitively, although Sub Saharan Africa bears 90% of the global malaria burden, resistance typically originates in regions where transmission intensity is low. In high transmission regions, infections are genetically diverse, and hosts have significant standing adaptive immunity, both of which are known to suppress the frequency of resistance within infections. However, interactions between immune-driven selection, transmission intensity, and resistance have not been investigated. Using a multiscale, agent-based model, we found that high transmission intensity slowed the evolution of resistance via its effect on host population immunity. High host immunity strengthened selection for antigenic novelty, interfering with selection for resistance and allowing sensitive lineages to suppress resistant lineages in untreated hosts. However, once resistance was common in the circulating parasite population, immune selection maintained it in the population at a high prevalence. Our findings provide a novel explanation for observations about the origin of resistance and suggest that adaptive immunity is a critical component of selection.
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Affiliation(s)
| | - Jonathan J. Juliano
- Division of Infectious Diseases, School of Medicine, University of North Carolina, Chapel Hill, North Carolina, United States of America
| | - Nicole Mideo
- Department of Ecology & Evolutionary Biology, University of Toronto, Toronto, Canada
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8
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Mathematical assessment of the impact of human-antibodies on sporogony during the within-mosquito dynamics of Plasmodium falciparum parasites. J Theor Biol 2020; 515:110562. [PMID: 33359209 DOI: 10.1016/j.jtbi.2020.110562] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2020] [Revised: 11/25/2020] [Accepted: 12/14/2020] [Indexed: 11/23/2022]
Abstract
We develop and analyze a deterministic ordinary differential equation mathematical model for the within-mosquito dynamics of the Plasmodium falciparum malaria parasite. Our model takes into account the action and effect of blood resident human-antibodies, ingested by the mosquito during a blood meal from humans, in inhibiting gamete fertilization. The model also captures subsequent developmental processes that lead to the different forms of the parasite within the mosquito. Continuous functions are used to model the switching transition from oocyst to sporozoites as well as human antibody density variations within the mosquito gut are proposed and used. In sum, our model integrates the developmental stages of the parasite within the mosquito such as gametogenesis, fertilization and sporogenesis culminating in the formation of sporozoites. Quantitative and qualitative analyses including a sensitivity analysis for influential parameters are performed. We quantify the average sporozoite load produced at the end of the within-mosquito malaria parasite's developmental stages. Our analysis shows that an increase in the efficiency of the ingested human antibodies in inhibiting fertilization within the mosquito's gut results in lowering the density of oocysts and hence sporozoites that are eventually produced by each mosquito vector. So, it is possible to control and limit oocysts development and hence sporozoites development within a mosquito by boosting the efficiency of antibodies as a pathway to the development of transmission-blocking vaccines which could potentially reduce oocysts prevalence among mosquitoes and hence reduce the transmission potential from mosquitoes to human.
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Ayala MJC, Villela DAM. Early transmission of sensitive strain slows down emergence of drug resistance in Plasmodium vivax. PLoS Comput Biol 2020; 16:e1007945. [PMID: 32555701 PMCID: PMC7363008 DOI: 10.1371/journal.pcbi.1007945] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2019] [Revised: 06/29/2020] [Accepted: 05/13/2020] [Indexed: 11/19/2022] Open
Abstract
The spread of drug resistance of Plasmodium falciparum and Plasmodium vivax parasites is a challenge towards malaria elimination. P. falciparum has shown an early and severe drug resistance in comparison to P. vivax in various countries. In fact, P. vivax differs in its life cycle and treatment in various factors: development and duration of sexual parasite forms differ, symptoms severity are unequal, relapses present only in P. vivax cases and the Artemisinin-based combination therapy (ACT) is only mandatory in P. falciparum cases. We compared the spread of drug resistance for both species through two compartmental models using ordinary differential equations. The model structure describes how sensitive and resistant parasite strains infect a human population treated with antimalarials. We found that an early transmission,i.e., before treatment and low effectiveness of drug coverage, supports the prevalence of sensitive parasites delaying the emergence of resistant P. vivax. These results imply that earlier attention of both symptomatic cases and reservoirs of P. vivax are essential in controlling transmission but also accelerate the spread of drug resistance.
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Affiliation(s)
- Mario J. C. Ayala
- Programa de Computação Científica, Fundação Oswaldo Cruz (Fiocruz), Rio de Janeiro, Brazil
| | - Daniel A. M. Villela
- Programa de Computação Científica, Fundação Oswaldo Cruz (Fiocruz), Rio de Janeiro, Brazil
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Evolution and Genetic Diversity of the k13 Gene Associated with Artemisinin Delayed Parasite Clearance in Plasmodium falciparum. Antimicrob Agents Chemother 2019; 63:AAC.02550-18. [PMID: 31085516 DOI: 10.1128/aac.02550-18] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2018] [Accepted: 04/28/2019] [Indexed: 01/19/2023] Open
Abstract
Mutations in the Plasmodium falciparum k13 (Pfk13) gene are linked to delayed parasite clearance in response to artemisinin-based combination therapies (ACTs) in Southeast Asia. To explore the evolutionary rate and constraints acting on this gene, k13 orthologs from species sharing a recent common ancestor with P. falciparum and Plasmodium vivax were analyzed. These comparative studies were followed by genetic polymorphism analyses within P. falciparum using 982 complete Pfk13 sequences from public databases and new data obtained by next-generation sequencing from African and Haitian isolates. Although k13 orthologs evolve at heterogeneous rates, the gene was conserved across the genus, with only synonymous substitutions being found at residues where mutations linked to the delayed parasite clearance phenotype have been reported. This suggests that those residues were under constraint from undergoing nonsynonymous changes during evolution of the genus. No fixed nonsynonymous differences were found between Pfk13 and its orthologs in closely related species found in African apes. This indicates that all nonsynonymous substitutions currently found in Pfk13 are younger than the time of divergence between P. falciparum and its closely related species. At the population level, no mutations linked to delayed parasite clearance were found in our samples from Africa and Haiti. However, there is a high number of single Pfk13 mutations segregating in P. falciparum populations, and two predominant alleles are distributed worldwide. This pattern is discussed in terms of how changes in the efficacy of natural selection, affected by population expansion, may have allowed for the emergence of mutations tolerant to ACTs.
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Orwa TO, Mbogo RW, Luboobi LS. Multiple-Strain Malaria Infection and Its Impacts on Plasmodium falciparum Resistance to Antimalarial Therapy: A Mathematical Modelling Perspective. COMPUTATIONAL AND MATHEMATICAL METHODS IN MEDICINE 2019; 2019:9783986. [PMID: 31341510 PMCID: PMC6594251 DOI: 10.1155/2019/9783986] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/14/2019] [Accepted: 05/15/2019] [Indexed: 11/18/2022]
Abstract
The emergence of parasite resistance to antimalarial drugs has contributed significantly to global human mortality and morbidity due to malaria infection. The impacts of multiple-strain malarial parasite infection have further generated a lot of scientific interest. In this paper, we demonstrate, using the epidemiological model, the effects of parasite resistance and competition between the strains on the dynamics and control of Plasmodium falciparum malaria. The analysed model has a trivial equilibrium point which is locally asymptotically stable when the parasite's effective reproduction number is less than unity. Using contour plots, we observed that the efficacy of antimalarial drugs used, the rate of development of resistance, and the rate of infection by merozoites are the most important parameters in the multiple-strain P. falciparum infection and control model. Although the drug-resistant strain is shown to be less fit, the presence of both strains in the human host has a huge impact on the cost and success of antimalarial treatment. To reduce the emergence of resistant strains, it is vital that only effective antimalarial drugs are administered to patients in hospitals, especially in malaria-endemic regions. Our results emphasize the call for regular and strict surveillance on the use and distribution of antimalarial drugs in health facilities in malaria-endemic countries.
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Affiliation(s)
- Titus Okello Orwa
- Institute of Mathematical Sciences, Strathmore University, P.O. Box 59857-00200, Nairobi, Kenya
| | - Rachel Waema Mbogo
- Institute of Mathematical Sciences, Strathmore University, P.O. Box 59857-00200, Nairobi, Kenya
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12
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Ocan M, Akena D, Nsobya S, Kamya MR, Senono R, Kinengyere AA, Obuku EA. Persistence of chloroquine resistance alleles in malaria endemic countries: a systematic review of burden and risk factors. Malar J 2019; 18:76. [PMID: 30871535 PMCID: PMC6419488 DOI: 10.1186/s12936-019-2716-z] [Citation(s) in RCA: 45] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2018] [Accepted: 03/08/2019] [Indexed: 12/18/2022] Open
Abstract
Background Chloroquine, a previous highly efficacious, easy to use and affordable anti-malarial agent was withdrawn from malaria endemic regions due to high levels of resistance. This review collated evidence from published-reviewed articles to establish prevalence of Pfcrt 76T and Pfmdr-1 86Y alleles in malaria affected countries following official discontinuation of chloroquine use. Methods A review protocol was developed, registered in PROSPERO (#CRD42018083957) and published in a peer-reviewed journal. Article search was done in PubMed, Scopus, Lilacs/Vhl and Embase databases by two experienced librarians (AK, RS) for the period 1990-to-Febuary 2018. Mesh terms and Boolean operators (AND, OR) were used. Data extraction form was designed in Excel spread sheet 2007. Data extraction was done by three reviewers (NL, BB and MO), discrepancies were resolved by discussion. Random effects analysis was done in Open Meta Analyst software. Heterogeneity was established using I2-statistic. Results A total of 4721 citations were retrieved from article search (Pubmed = 361, Lilac/vhl = 28, Science Direct = 944, Scopus = 3388). Additional targeted search resulted in three (03) eligible articles. After removal of duplicates (n = 523) and screening, 38 articles were included in the final review. Average genotyping success rate was 63.6% (18,343/28,820) for Pfcrt K76T and 93.5% (16,232/17,365) for Pfmdr-1 86Y mutations. Prevalence of Pfcrt 76T was as follows; East Africa 48.9% (2528/5242), Southern Africa 18.6% (373/2163), West Africa 58.3% (3321/6608), Asia 80.2% (1951/2436). Prevalence of Pfmdr-1 86Y was; East Africa 32.4% (1447/5722), Southern Africa 36.1% (544/1640), West Africa 52.2% (1986/4200), Asia 46.4% (1276/2217). Over half, 52.6% (20/38) of included studies reported continued unofficial chloroquine use following policy change. Studies done in Madagascar and Kenya reported re-emergence of chloroquine sensitive parasites (IC50 < 30.9 nM). The average time (years) since discontinuation of chloroquine use to data collection was 8.7 ± 7.4. There was high heterogeneity (I2 > 95%). Conclusion The prevalence of chloroquine resistance alleles among Plasmodium falciparum parasites have steadily declined since discontinuation of chloroquine use. However, Pfcrt K76T and Pfmdr-1 N86Y mutations still persist at moderate frequencies in most malaria affected countries.
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Affiliation(s)
- Moses Ocan
- Department of Pharmacology & Therapeutics, Makerere University, P.O. Box 7072, Kampala, Uganda. .,Africa Centre for Systematic Reviews and Knowledge Translation, Makerere University College of Health Sciences, P.O. Box 7072, Kampala, Uganda.
| | - Dickens Akena
- Department of Psychiatry, Makerere University, P.O. Box 7072, Kampala, Uganda.,Infectious Disease Institute, Makerere University, P. O. Box 22418, Kampala, Uganda
| | - Sam Nsobya
- Department of Medical Microbiology, Makerere University, P.O. Box 7072, Kampala, Uganda
| | - Moses R Kamya
- Department of Medicine, Makerere University, P.O. Box 7072, Kampala, Uganda
| | - Richard Senono
- Infectious Disease Institute, Makerere University, P. O. Box 22418, Kampala, Uganda.,Africa Centre for Systematic Reviews and Knowledge Translation, Makerere University College of Health Sciences, P.O. Box 7072, Kampala, Uganda
| | - Alison Annet Kinengyere
- Albert Cook Library, Makerere University, P.O. Box 7072, Kampala, Uganda.,Africa Centre for Systematic Reviews and Knowledge Translation, Makerere University College of Health Sciences, P.O. Box 7072, Kampala, Uganda
| | - Ekwaro A Obuku
- Clinical Epidemiology Unit, Department of Medicine, Makerere University, P.O. Box 7072, Kampala, Uganda.,Africa Centre for Systematic Reviews and Knowledge Translation, Makerere University College of Health Sciences, P.O. Box 7072, Kampala, Uganda.,Faculty of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, London, UK
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13
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Intermittent Preventive Treatment (IPT): Its Role in Averting Disease-Induced Mortality in Children and in Promoting the Spread of Antimalarial Drug Resistance. Bull Math Biol 2018; 81:193-234. [PMID: 30382460 PMCID: PMC6320360 DOI: 10.1007/s11538-018-0524-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2017] [Accepted: 10/09/2018] [Indexed: 11/03/2022]
Abstract
We develop an age-structured ODE model to investigate the role of intermittent preventive treatment (IPT) in averting malaria-induced mortality in children, and its related cost in promoting the spread of antimalarial drug resistance. IPT, a malaria control strategy in which a full curative dose of an antimalarial medication is administered to vulnerable asymptomatic individuals at specified intervals, has been shown to reduce malaria transmission and deaths in children and pregnant women. However, it can also promote drug resistance spread. Our mathematical model is used to explore IPT effects on drug resistance and deaths averted in holoendemic malaria regions. The model includes drug-sensitive and drug-resistant strains as well as human hosts and mosquitoes. The basic reproduction, and invasion reproduction numbers for both strains are derived. Numerical simulations show the individual and combined effects of IPT and treatment of symptomatic infections on the prevalence of both strains and the number of lives saved. Our results suggest that while IPT can indeed save lives, particularly in high transmission regions, certain combinations of drugs used for IPT and to treat symptomatic infection may result in more deaths when resistant parasite strains are circulating. Moreover, the half-lives of the treatment and IPT drugs used play an important role in the extent to which IPT may influence spread of the resistant strain. A sensitivity analysis indicates the model outcomes are most sensitive to the reduction factor of transmission for the resistant strain, rate of immunity loss, and the natural clearance rate of sensitive infections.
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14
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Okell LC, Reiter LM, Ebbe LS, Baraka V, Bisanzio D, Watson OJ, Bennett A, Verity R, Gething P, Roper C, Alifrangis M. Emerging implications of policies on malaria treatment: genetic changes in the Pfmdr-1 gene affecting susceptibility to artemether-lumefantrine and artesunate-amodiaquine in Africa. BMJ Glob Health 2018; 3:e000999. [PMID: 30397515 PMCID: PMC6202998 DOI: 10.1136/bmjgh-2018-000999] [Citation(s) in RCA: 55] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2018] [Revised: 08/21/2018] [Accepted: 08/31/2018] [Indexed: 11/04/2022] Open
Abstract
Artemether–lumefantrine (AL) and artesunate–amodiaquine (AS-AQ) are the most commonly used artemisinin-based combination therapies (ACT) for treatment of Plasmodium falciparum in Africa. Both treatments remain efficacious, but single nucleotide polymorphisms (SNPs) in the Plasmodium falciparum multidrug resistance 1 (Pfmdr1) gene may compromise sensitivity. AL and AS-AQ exert opposing selective pressures: parasites with genotype 86Y, Y184 and 1246Y are partially resistant to AS-AQ treatment, while N86, 184 F and D1246 are favoured by AL treatment. Through a systematic review, we identified 397 surveys measuring the prevalence of Pfmdr1 polymorphisms at positions 86 184 or 1246 in 30 countries in Africa. Temporal trends in SNP frequencies after introduction of AL or AS-AQ as first-line treatment were analysed in 32 locations, and selection coefficients estimated. We examined associations between antimalarial policies, consumption, transmission intensity and rate of SNP selection. 1246Y frequency decreased on average more rapidly in locations where national policy recommended AL (median selection coefficient(s) of −0.083), compared with policies of AS-AQ or both AL and AS-AQ (median s=−0.035 and 0.021, p<0.001 respectively). 86Y frequency declined markedly after ACT policy introduction, with a borderline significant trend for a more rapid decline in countries with AL policies (p=0.055). However, these trends could also be explained by a difference in initial SNP frequencies at the time of ACT introduction. There were non-significant trends for faster selection of N86 and D1246 in areas with higher AL consumption and no trend with transmission intensity. Recorded consumption of AS-AQ was low in the locations and times Pfmdr1 data were collected. SNP trends in countries with AL policies suggest a broad increase in sensitivity of parasites to AS-AQ, by 7–10 years after AL introduction. Observed rates of selection have implications for planning strategies to cycle drugs or use multiple first-line therapies to maintain drug efficacy.
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Affiliation(s)
- Lucy C Okell
- MRC Centre for Outbreak Analysis and Modelling, Department of Infectious Disease Epidemiology, Imperial College London, London, UK
| | - Lisa Malene Reiter
- Global Health Section, Department of Public Health, University of Copenhagen, Copenhagen, Denmark
| | - Lene Sandø Ebbe
- Centre for Medical Parasitology, Department of Immunology and Microbiology, University of Copenhagen, Copenhagen, Denmark.,Department of Infectious Disease, Copenhagen University Hospital, Copenhagen, Denmark
| | - Vito Baraka
- Department of Biomedical Sciences, National Institute for Medical Research, Tanga, United Republic of Tanzania
| | - Donal Bisanzio
- RTI International, Washington, District of Columbia, USA
| | - Oliver J Watson
- MRC Centre for Outbreak Analysis and Modelling, Department of Infectious Disease Epidemiology, Imperial College London, London, UK
| | - Adam Bennett
- Malaria Elimination Initiative, Global Health Group, University of San FranciscO, San Francisco, California, USA
| | - Robert Verity
- MRC Centre for Outbreak Analysis and Modelling, Department of Infectious Disease Epidemiology, Imperial College London, London, UK
| | - Peter Gething
- Malaria Atlas Project, Oxford Big Data Institute, Li Ka Shing Centre for Health Information and Discovery, Nuffield Department of Medicine, University of Oxford, Oxford, UK
| | - Cally Roper
- Department of Pathogen Molecular Biology, London School of Hygiene and Tropical Medicine, London, UK
| | - Michael Alifrangis
- Centre for Medical Parasitology, Department of Immunology and Microbiology, University of Copenhagen, Copenhagen, Denmark
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15
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Tompkins AM, Thomson MC. Uncertainty in malaria simulations in the highlands of Kenya: Relative contributions of model parameter setting, driving climate and initial condition errors. PLoS One 2018; 13:e0200638. [PMID: 30256799 PMCID: PMC6157844 DOI: 10.1371/journal.pone.0200638] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2017] [Accepted: 06/29/2018] [Indexed: 11/23/2022] Open
Abstract
In this study, experiments are conducted to gauge the relative importance of model, initial condition, and driving climate uncertainty for simulations of malaria transmission at a highland plantation in Kericho, Kenya. A genetic algorithm calibrates each of these three factors within their assessed prior uncertainty in turn to see which allows the best fit to a timeseries of confirmed cases. It is shown that for high altitude locations close to the threshold for transmission, the spatial representativeness uncertainty for climate, in particular temperature, dominates the uncertainty due to model parameter settings. Initial condition uncertainty plays little role after the first two years, and is thus important in the early warning system context, but negligible for decadal and climate change investigations. Thus, while reducing uncertainty in the model parameters would improve the quality of the simulations, the uncertainty in the temperature driving data is critical. It is emphasized that this result is a function of the mean climate of the location itself, and it is shown that model uncertainty would be relatively more important at warmer, lower altitude locations.
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Affiliation(s)
- Adrian M. Tompkins
- Earth System Physics, The Abdus Salam International Centre for Theoretical Physics (ICTP), Strada Costiera 11, Trieste, Italy
- * E-mail:
| | - Madeleine C. Thomson
- International Research Institute for Climate and Society, Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York, United States of America
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16
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Bushman M, Antia R, Udhayakumar V, de Roode JC. Within-host competition can delay evolution of drug resistance in malaria. PLoS Biol 2018; 16:e2005712. [PMID: 30130363 PMCID: PMC6103507 DOI: 10.1371/journal.pbio.2005712] [Citation(s) in RCA: 37] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2018] [Accepted: 07/16/2018] [Indexed: 12/21/2022] Open
Abstract
In the malaria parasite P. falciparum, drug resistance generally evolves first in low-transmission settings, such as Southeast Asia and South America. Resistance takes noticeably longer to appear in the high-transmission settings of sub-Saharan Africa, although it may spread rapidly thereafter. Here, we test the hypothesis that competitive suppression of drug-resistant parasites by drug-sensitive parasites may inhibit evolution of resistance in high-transmission settings, where mixed-strain infections are common. We employ a cross-scale model, which simulates within-host (infection) dynamics and between-host (transmission) dynamics of sensitive and resistant parasites for a population of humans and mosquitoes. Using this model, we examine the effects of transmission intensity, selection pressure, fitness costs of resistance, and cross-reactivity between strains on the establishment and spread of resistant parasites. We find that resistant parasites, introduced into the population at a low frequency, are more likely to go extinct in high-transmission settings, where drug-sensitive competitors and high levels of acquired immunity reduce the absolute fitness of the resistant parasites. Under strong selection from antimalarial drug use, however, resistance spreads faster in high-transmission settings than low-transmission ones. These contrasting results highlight the distinction between establishment and spread of resistance and suggest that the former but not the latter may be inhibited in high-transmission settings. Our results suggest that within-host competition is a key factor shaping the evolution of drug resistance in P. falciparum. The malaria parasite Plasmodium falciparum has evolved resistance to most antimalarial drugs, greatly complicating treatment and control of the disease. Curiously, although sub-Saharan Africa accounts for the majority of the global burden of malaria, the evolution of drug resistance in Africa has been markedly delayed compared to Asia and the Americas. One reason might be that, in a population in which the prevalence of infection is high, a newly emerged drug-resistant strain faces a high risk of extinction due to competition from drug-sensitive parasites that already “occupy” most of the host population. Using a mathematical model, we confirm that drug-resistant parasites face a much greater risk of extinction in a “high-transmission” setting like sub-Saharan Africa than in a “low-transmission” setting like Southeast Asia. However, we also find that when drug-resistant parasites manage to avoid extinction, their subsequent spread may be more rapid in high-transmission settings than in low-transmission settings, especially when selection is strong. These results offer a novel explanation for global patterns of drug resistance evolution in malaria and suggest a new dimension to consider in resistance prevention and containment efforts: namely, the intrinsic favorability of low- and high-transmission settings for establishment and spread of drug resistance.
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Affiliation(s)
- Mary Bushman
- Department of Biology, Emory University, Atlanta, Georgia, United States of America
- * E-mail:
| | - Rustom Antia
- Department of Biology, Emory University, Atlanta, Georgia, United States of America
| | - Venkatachalam Udhayakumar
- Malaria Branch, Division of Parasitic Diseases and Malaria, Center for Global Health, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America
| | - Jacobus C. de Roode
- Department of Biology, Emory University, Atlanta, Georgia, United States of America
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17
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Scott N, Ataide R, Wilson DP, Hellard M, Price RN, Simpson JA, Fowkes FJI. Implications of population-level immunity for the emergence of artemisinin-resistant malaria: a mathematical model. Malar J 2018; 17:279. [PMID: 30071877 PMCID: PMC6071336 DOI: 10.1186/s12936-018-2418-y] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2018] [Accepted: 07/12/2018] [Indexed: 01/12/2023] Open
Abstract
BACKGROUND Artemisinin-resistant Plasmodium falciparum has emerged in the Greater Mekong Subregion, an area of relatively low transmission, but has yet to be reported in Africa. A population-based mathematical model was used to investigate the relationship between P. falciparum prevalence, exposure-acquired immunity and time-to-emergence of artemisinin resistance. The possible implication for the emergence of resistance across Africa was assessed. METHODS The model included human and mosquito populations, two strains of malaria ("wild-type", "mutant"), three levels of human exposure-acquired immunity (none, low, high) with two types of immunity for each level (sporozoite/liver stage immunity and blood-stage/gametocyte immunity) and drug pressure based on per-capita treatment numbers. RESULTS The model predicted that artemisinin-resistant strains may circulate up to 10 years longer in high compared to low P. falciparum prevalence areas before resistance is confirmed. Decreased time-to-resistance in low prevalence areas was explained by low genetic diversity and immunity, which resulted in increased probability of selection and spread of artemisinin-resistant strains. Artemisinin resistance was estimated to be established by 2020 in areas of Africa with low (< 10%) P. falciparum prevalence, but not for 5 or 10 years later in moderate (10-25%) or high (> 25%) prevalence areas, respectively. CONCLUSIONS Areas of low transmission and low immunity give rise to a more rapid expansion of artemisinin-resistant parasites, corroborating historical observations of anti-malarial resistance emergence. Populations where control strategies are in place that reduce malaria transmission, and hence immunity, may be prone to a rapid emergence and spread of artemisinin-resistant strains and thus should be carefully monitored.
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Affiliation(s)
- Nick Scott
- Disease Elimination Program, Burnet Institute, Melbourne, VIC, 3004, Australia
- Department of Epidemiology and Preventive Medicine, Monash University, Melbourne, VIC, 3004, Australia
| | - Ricardo Ataide
- Disease Elimination Program, Burnet Institute, Melbourne, VIC, 3004, Australia
| | - David P Wilson
- Disease Elimination Program, Burnet Institute, Melbourne, VIC, 3004, Australia
- Department of Epidemiology and Preventive Medicine, Monash University, Melbourne, VIC, 3004, Australia
| | - Margaret Hellard
- Disease Elimination Program, Burnet Institute, Melbourne, VIC, 3004, Australia
- Department of Epidemiology and Preventive Medicine, Monash University, Melbourne, VIC, 3004, Australia
- Department of Infectious Diseases, Alfred Hospital, Melbourne, VIC, 3004, Australia
| | - Ric N Price
- Global and Tropical Health Division, Menzies School of Health Research, Charles Darwin University, Darwin, NT, Australia
- Centre for Tropical Medicine and Global Health, Nuffield Department of Clinical Medicine, University of Oxford, Oxford, UK
| | - Julie A Simpson
- Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, The University of Melbourne, Melbourne, VIC, 3010, Australia
| | - Freya J I Fowkes
- Disease Elimination Program, Burnet Institute, Melbourne, VIC, 3004, Australia.
- Department of Epidemiology and Preventive Medicine, Monash University, Melbourne, VIC, 3004, Australia.
- Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, The University of Melbourne, Melbourne, VIC, 3010, Australia.
- Department of Infectious Diseases, Monash University, Melbourne, VIC, 3004, Australia.
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18
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Huijben S, Chan BHK, Nelson WA, Read AF. The impact of within-host ecology on the fitness of a drug-resistant parasite. EVOLUTION MEDICINE AND PUBLIC HEALTH 2018; 2018:127-137. [PMID: 30087774 PMCID: PMC6061792 DOI: 10.1093/emph/eoy016] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/26/2018] [Accepted: 06/18/2018] [Indexed: 02/05/2023]
Abstract
Background and objectives The rate of evolution of drug resistance depends on the fitness of resistant pathogens. The fitness of resistant pathogens is reduced by competition with sensitive pathogens in untreated hosts and so enhanced by competitive release in drug-treated hosts. We set out to estimate the magnitude of those effects on a variety of fitness measures, hypothesizing that competitive suppression and competitive release would have larger impacts when resistance was rarer to begin with. Methodology We infected mice with varying densities of drug-resistant Plasmodium chabaudi malaria parasites in a fixed density of drug-sensitive parasites and followed infection dynamics using strain-specific quantitative PCR. Results Competition with susceptible parasites reduced the absolute fitness of resistant parasites by 50–100%. Drug treatment increased the absolute fitness from 2- to >10 000-fold. The ecological context and choice of fitness measure was responsible for the wide variation in those estimates. Initial population growth rates poorly predicted parasite abundance and transmission probabilities. Conclusions and implications (i) The sensitivity of estimates of pathogen fitness to ecological context and choice of fitness measure make it difficult to derive field-relevant estimates of the fitness costs and benefits of resistance from experimental settings. (ii) Competitive suppression can be a key force preventing resistance from emerging when it is rare, as it is when it first arises. (iii) Drug treatment profoundly affects the fitness of resistance. Resistance evolution could be slowed by developing drug use policies that consider in-host competition.
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Affiliation(s)
- Silvie Huijben
- Departments of Biology and Entomology, Center for Infectious Disease Dynamics, Pennsylvania State University, University Park, PA, USA
| | - Brian H K Chan
- Departments of Biology and Entomology, Center for Infectious Disease Dynamics, Pennsylvania State University, University Park, PA, USA
| | - William A Nelson
- Department of Biology, Queen's University, Kingston, ON K7L3N6, Canada
| | - Andrew F Read
- Departments of Biology and Entomology, Center for Infectious Disease Dynamics, Pennsylvania State University, University Park, PA, USA.,Department of Fogarty, National Institutes of Health, Fogarty International Center, Bethesda, MD, USA
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19
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The role of antimalarial quality in the emergence and transmission of resistance. Med Hypotheses 2017; 111:49-54. [PMID: 29406996 DOI: 10.1016/j.mehy.2017.12.018] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2017] [Revised: 11/14/2017] [Accepted: 12/13/2017] [Indexed: 11/23/2022]
Abstract
The emergence and transmission of antimalarial resistance is hampering malaria eradication efforts and is shortening the useful therapeutic life of currently available antimalarials. Drug selection pressure has been identified as a contributing factor to the emergence and transmission of resistance, especially population treatment coverage and sub-therapeutic concentrations of active pharmaceutical ingredient (API) in the bloodstream. Medicine quality can be defined as good quality or poor quality. Poor quality antimalarials can be falsified, substandard or degraded and are estimated to make up between 10 and 50% of the antimalarial market in developing countries, and can be a source of sub-therapeutic doses of antimalarial API(s). The availability and use of poor quality antimalarials and the non-recommended use of quality assured monotherapies have historically been linked to treatment failure and in some cases, have coincided with the emergence and transmission of resistance in regions. We propose and outline the hypotheses that the use of poor quality antimalarial treatments and non-recommended quality assured monotherapies promote the (i) emergence and/or (ii) transmission of antimalarial resistance.
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20
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The Impact of Antimalarial Use on the Emergence and Transmission of Plasmodium falciparum Resistance: A Scoping Review of Mathematical Models. Trop Med Infect Dis 2017; 2:tropicalmed2040054. [PMID: 30270911 PMCID: PMC6082068 DOI: 10.3390/tropicalmed2040054] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2017] [Revised: 10/04/2017] [Accepted: 10/06/2017] [Indexed: 01/08/2023] Open
Abstract
The emergence and transmission of resistance to antimalarial treatments continue to hamper malaria elimination efforts. A scoping review was undertaken regarding the impact of antimalarial treatment in the human population on the emergence and transmission of Plasmodium falciparum resistance, to (i) describe the use of mathematical models used to explore this relationship; (ii) discuss model findings; and (iii) identify factors influencing the emergence and transmission of resistance. Search strategies were developed and deployed in six major databases. Thirty-seven articles met the eligibility criteria and were included in the review: nine articles modeled the emergence of resistance, 19 modeled the transmission of resistance, and nine modeled both the emergence and transmission. The proportion of antimalarial use within the population and the presence of residual drug concentrations were identified to be the main predictors of the emergence and transmission of resistance. Influencing factors pertaining to the human, parasite and mosquito populations are discussed. To ensure the prolonged therapeutic usefulness of antimalarial treatments, the effect of antimalarial drug use on the emergence and transmission of resistance must be understood, and mathematical models are a useful tool for exploring these dynamics.
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21
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Ataíde R, Powell R, Moore K, McLean A, Phyo AP, Nair S, White M, Anderson TJ, Beeson JG, Simpson JA, Nosten F, Fowkes FJI. Declining Transmission and Immunity to Malaria and Emerging Artemisinin Resistance in Thailand: A Longitudinal Study. J Infect Dis 2017; 216:723-731. [PMID: 28934435 PMCID: PMC5853569 DOI: 10.1093/infdis/jix371] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Background Reductions in malaria transmission decrease naturally acquired immunity, which may influence the emergence of Plasmodium falciparum artemisinin-resistant phenotypes and genotypes over time. Methods Antibodies specific for P. falciparum antigens were determined in uncomplicated hyperparasitemic malaria patients over a 10-year period of declining malaria transmission and emerging artemisinin resistance in northwestern Thailand. We investigated the association between antibody levels and both parasite clearance time (PCt½) and artemisinin resistance–associated kelch13 genotypes over time. Results Immunity to P. falciparum declined prior to 2004, preceding the emergence of artemisinin resistance-associated genotypes and phenotypes (maximum mean change in antibody level per year: anti-MSP142 = −0.17; 95% confidence interval [CI] = −.31 to −.04; P = .01). In this period of declining immunity, and in the absence of kelch13 mutations, PCt½ increased. Between 2007 and 2011, levels of antibodies fluctuated, and higher antibody levels were associated with faster PCt½ (maximum yearly change in PCt½, in hours: EBA140rII = −0.39; 95% CI = −.61 to −.17; P < .001). Conclusions Understanding the impact of changing transmission and immunity on the emergence of artemisinin resistance is important particularly as increased malaria control and elimination activities may enhance immunological conditions for the expansion of artemisinin-resistant P. falciparum.
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Affiliation(s)
| | | | | | | | - Aung Pyae Phyo
- Shoklo Malaria Research Unit, Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Mae Sot,Thailand
| | - Shalini Nair
- Texas Biomedical Research Institute, San Antonio
| | - Marina White
- Texas Biomedical Research Institute, San Antonio
| | | | | | - Julie A Simpson
- Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, University of Melbourne
| | - Francois Nosten
- Shoklo Malaria Research Unit, Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Mae Sot, Thailand.,Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine Research, University of Oxford, United Kingdom
| | - Freya J I Fowkes
- Disease Elimination Program, Burnet Institute.,Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, University of Melbourne.,Department of Epidemiology and Preventive Medicine, Department of Infectious Diseases, Monash University, Melbourne, Australia
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22
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Brock AR, Ross JV, Greenhalgh S, Durham DP, Galvani A, Parikh S, Esterman A. Modelling the impact of antimalarial quality on the transmission of sulfadoxine-pyrimethamine resistance in Plasmodium falciparum. Infect Dis Model 2017; 2:161-187. [PMID: 29928735 PMCID: PMC6001968 DOI: 10.1016/j.idm.2017.04.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2016] [Revised: 04/10/2017] [Accepted: 04/11/2017] [Indexed: 12/26/2022] Open
Abstract
Background The use of poor quality antimalarial medicines, including the use of non-recommended medicines for treatment such as sulfadoxine-pyrimethamine (SP) monotherapy, undermines malaria control and elimination efforts. Furthermore, the use of subtherapeutic doses of the active ingredient(s) can theoretically promote the emergence and transmission of drug resistant parasites. Methods We developed a deterministic compartmental model to quantify the impact of antimalarial medicine quality on the transmission of SP resistance, and validated it using sensitivity analysis and a comparison with data from Kenya collected in 2006. We modelled human and mosquito population dynamics, incorporating two Plasmodium falciparum subtypes (SP-sensitive and SP-resistant) and both poor quality and good quality (artemether-lumefantrine) antimalarial use. Findings The model predicted that an increase in human malaria cases, and among these, an increase in the proportion of SP-resistant infections, resulted from an increase in poor quality SP antimalarial use, whether it was full- or half-dose SP monotherapy. Interpretation Our findings suggest that an increase in poor quality antimalarial use predicts an increase in the transmission of resistance. This highlights the need for stricter control and regulation on the availability and use of poor quality antimalarial medicines, in order to offer safe and effective treatments, and work towards the eradication of malaria.
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Affiliation(s)
- Aleisha R Brock
- School of Nursing & Midwifery, University of South Australia, Adelaide, SA, Australia
| | - Joshua V Ross
- School of Mathematical Sciences, The University of Adelaide, Adelaide, SA, Australia
| | - Scott Greenhalgh
- Department of Mathematics and Statistics, Queen's University, Kingston, ON, Canada
| | - David P Durham
- Center for Infectious Disease Modeling and Analysis, Yale School of Public Health, New Haven, CT, USA
| | - Alison Galvani
- Center for Infectious Disease Modeling and Analysis, Yale School of Public Health, New Haven, CT, USA
| | - Sunil Parikh
- Yale School of Public Health, New Haven, CT, USA
| | - Adrian Esterman
- Sansom Institute for Research Health, University of South Australia, Adelaide, SA, Australia.,Australian Institute of Tropical Health and Medicine, James Cook University, Cairns, QLD, Australia
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23
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Evaluation of the Parasight Platform for Malaria Diagnosis. J Clin Microbiol 2016; 55:768-775. [PMID: 27974542 DOI: 10.1128/jcm.02155-16] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2016] [Accepted: 12/04/2016] [Indexed: 11/20/2022] Open
Abstract
The World Health Organization estimates that nearly 500 million malaria tests are performed annually. While microscopy and rapid diagnostic tests (RDTs) are the main diagnostic approaches, no single method is inexpensive, rapid, and highly accurate. Two recent studies from our group have demonstrated a prototype computer vision platform that meets those needs. Here we present the results from two clinical studies on the commercially available version of this technology, the Sight Diagnostics Parasight platform, which provides malaria diagnosis, species identification, and parasite quantification. We conducted a multisite trial in Chennai, India (Apollo Hospital [n = 205]), and Nairobi, Kenya (Aga Khan University Hospital [n = 263]), in which we compared the device to microscopy, RDTs, and PCR. For identification of malaria, the device performed similarly well in both contexts (sensitivity of 99% and specificity of 100% at the Indian site and sensitivity of 99.3% and specificity of 98.9% at the Kenyan site, compared to PCR). For species identification, the device correctly identified 100% of samples with Plasmodium vivax and 100% of samples with Plasmodium falciparum in India and 100% of samples with P. vivax and 96.1% of samples with P. falciparum in Kenya, compared to PCR. Lastly, comparisons of the device parasite counts with those of trained microscopists produced average Pearson correlation coefficients of 0.84 at the Indian site and 0.85 at the Kenyan site.
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24
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Bassat Q, Tanner M, Guerin PJ, Stricker K, Hamed K. Combating poor-quality anti-malarial medicines: a call to action. Malar J 2016; 15:302. [PMID: 27251199 PMCID: PMC4888506 DOI: 10.1186/s12936-016-1357-8] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2016] [Accepted: 05/24/2016] [Indexed: 12/04/2022] Open
Abstract
The circulation of poor-quality medicines continues to undermine the fight against many life-threatening diseases. Anti-malarial medicines appear to have been particularly compromised and present a major public health threat in malaria-endemic countries, negatively affecting individuals and their communities. Concerted collaborative efforts are required from global, regional and national organizations, involving the public and private sectors, to address the problem. While many initiatives are underway, a number of unmet needs deserve urgent and increased multisector attention. At the global level, there is a need for an international public health legal framework or treaty on poor-quality medicines, with statutes suitable for integration into national laws. In addition, increased international efforts are required to strengthen the governance of global supply chains and enhance cooperation between national medicine regulation authorities and law enforcement bodies. Increased investment is needed in innovative technologies that will enable healthcare teams to detect poor-quality medicines at all levels of the supply chain. At the regional level, a number of initiatives would be beneficial—key areas are standardization, simplification, and reciprocal recognition of registration processes and development of quality control capacity in regional centres of excellence that are better aligned with public health needs; improved surveillance methods and creation of a framework for compulsory and transparent reporting of poor-quality medicines; additional support for national medicine regulation authorities and other national partner authorities; and an increase in support for regional laboratories to boost their capabilities in detecting poor-quality medicines. It is vital that all stakeholders involved in efforts against poor-quality anti-malarial medicines extend and strengthen their actions in these critical areas and thus effectively support global health development and malaria elimination programmes.
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Affiliation(s)
- Quique Bassat
- Centro de Investigação Em Saúde Da Manhiça (CISM), Maputo, Mozambique.,ISGlobal, Barcelona Centre for International Health Research (CRESIB), Hospital Clínic-Universitat de Barcelona, Barcelona, Spain
| | - Marcel Tanner
- Swiss Tropical and Public Health Institute, Basel, Switzerland.,University of Basel, Basel, Switzerland
| | - Philippe J Guerin
- WorldWide Antimalarial Resistance Network, Oxford, UK.,Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, Oxford University, Oxford, UK
| | | | - Kamal Hamed
- Novartis Pharmaceuticals Corporation, East Hanover, NJ, USA.
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Chang HH, Childs LM, Buckee CO. Variation in infection length and superinfection enhance selection efficiency in the human malaria parasite. Sci Rep 2016; 6:26370. [PMID: 27193195 PMCID: PMC4872237 DOI: 10.1038/srep26370] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2015] [Accepted: 04/28/2016] [Indexed: 01/08/2023] Open
Abstract
The capacity for adaptation is central to the evolutionary success of the human malaria parasite Plasmodium falciparum. Malaria epidemiology is characterized by the circulation of multiple, genetically diverse parasite clones, frequent superinfection, and highly variable infection lengths, a large number of which are chronic and asymptomatic. The impact of these characteristics on the evolution of the parasite is largely unknown, however, hampering our understanding of the impact of interventions and the emergence of drug resistance. In particular, standard population genetic frameworks do not accommodate variation in infection length or superinfection. Here, we develop a population genetic model of malaria including these variations, and show that these aspects of malaria infection dynamics enhance both the probability and speed of fixation for beneficial alleles in complex and non-intuitive ways. We find that populations containing a mixture of short- and long-lived infections promote selection efficiency. Interestingly, this increase in selection efficiency occurs even when only a small fraction of the infections are chronic, suggesting that selection can occur efficiently in areas of low transmission intensity, providing a hypothesis for the repeated emergence of drug resistance in the low transmission setting of Southeast Asia.
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Affiliation(s)
- Hsiao-Han Chang
- Center for Communicable Disease Dynamics, Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, MA 02115, USA
| | - Lauren M Childs
- Center for Communicable Disease Dynamics, Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, MA 02115, USA
| | - Caroline O Buckee
- Center for Communicable Disease Dynamics, Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, MA 02115, USA
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Klein EY, Smith DL, Cohen JM, Laxminarayan R. Bioeconomic analysis of child-targeted subsidies for artemisinin combination therapies: a cost-effectiveness analysis. J R Soc Interface 2016; 12:rsif.2014.1356. [PMID: 25994293 PMCID: PMC4590492 DOI: 10.1098/rsif.2014.1356] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The Affordable Medicines Facility for malaria (AMFm) was conceived as a global market-based mechanism to increase access to effective malaria treatment and prolong effectiveness of artemisinin. Although results from a pilot implementation suggested that the subsidy was effective in increasing access to high-quality artemisinin combination therapies (ACTs), the Global Fund has converted AMFm into a country-driven mechanism whereby individual countries could choose to fund the subsidy from within their country envelopes. Because the initial costs of the subsidy in the pilot countries was higher than expected, countries are also exploring alternatives to a universal subsidy, such as subsidizing only child doses. We examined the incremental cost-effectiveness of a child-targeted policy using an age-structured bioeconomic model of malaria from the provider perspective. Because the vast majority of malaria deaths occur in children, targeting children could potentially improve the cost-effectiveness of the subsidy, though it would avert significantly fewer deaths. However, the benefits of a child-targeted subsidy (i.e. deaths averted) are eroded as leakage (i.e. older individuals taking young child-targeted doses) increases, with few of the benefits of a universal subsidy gained (i.e. reductions in overall prevalence). Although potentially more cost-effective, a child-targeted subsidy must contain measures to reduce the possibility of leakage.
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Affiliation(s)
- Eili Y Klein
- Center for Disease Dynamics, Economics and Policy, Washington, DC, USA Department of Emergency Medicine, Johns Hopkins University, Baltimore, MD, USA
| | - David L Smith
- Department of Zoology, University of Oxford, Oxford, UK Sanaria Institute for Global Health & Tropical Medicine, Rockville, MD, USA
| | | | - Ramanan Laxminarayan
- Center for Disease Dynamics, Economics and Policy, Washington, DC, USA Princeton Environmental Institute, Princeton University, Princeton, NJ, USA Public Health Foundation of India, New Delhi, India
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Ingasia LA, Cheruiyot J, Okoth SA, Andagalu B, Kamau E. Genetic variability and population structure of Plasmodium falciparum parasite populations from different malaria ecological regions of Kenya. INFECTION GENETICS AND EVOLUTION 2015; 39:372-380. [PMID: 26472129 DOI: 10.1016/j.meegid.2015.10.013] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/02/2015] [Revised: 10/09/2015] [Accepted: 10/10/2015] [Indexed: 10/22/2022]
Abstract
Transmission intensity, movement of human and vector hosts, biogeographical features, and malaria control measures are some of the important factors that determine Plasmodium falciparum parasite genetic variability and population structure. Kenya has different malaria ecologies which might require different disease intervention methods. Refined parasite population genetic studies are critical for informing malaria control and elimination strategies. This study describes the genetic diversity and population structure of P. falciparum parasites from the different malaria ecological zones in Kenya. Twelve multi-locus microsatellite (MS) loci previously described were genotyped in 225 P. falciparum isolates collected between 2012 and 2013 from five sites; three in lowland endemic regions (Kisumu, Kombewa, and Malindi) and two in highland, epidemic regions (Kisii and Kericho). Parasites from the lowland endemic and highland epidemic regions of western Kenya had high genetic diversity compared to coastal lowland endemic region of Kenya [Malindi]. The Kenyan parasites had a mean genetic differentiation index (FST) of 0.072 (p=0.011). The multi-locus genetic analysis of the 12 MS revealed all the parasites had unique haplotypes. Significant linkage disequilibrium (LD) was observed in all the five parasite populations. Kisumu had the most significant index of association values (0.16; p<0.0001) whereas Kisii had the least significant index of association values (0.03; p<0.0001). Our data suggest high genetic diversity in Kenyan parasite population with the exception of parasite from Malindi where malaria has been on the decline. The presence of significant LD suggests that there is occurrence of inbreeding in the parasite population. Parasite populations from Kisii showed the strongest evidence for epidemic population structure whereas the rest of the regions showed panmixia. Defining the genetic diversity of the parasites in different ecological regions of Kenya after introduction of the artemether-lumefantrine is important in refining the spread of drug resistant strains and malaria transmission for more effective control and eventual elimination of malaria in Kenya.
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Affiliation(s)
- Luicer A Ingasia
- Department of Emerging and Infectious Diseases (DEID), United States Army Medical Research Directorate-Kenya (USAMRD-K), Kenya Medical Research Institute (KEMRI)/Walter Reed Project (WRP), Kisumu, Kenya
| | - Jelagat Cheruiyot
- Department of Emerging and Infectious Diseases (DEID), United States Army Medical Research Directorate-Kenya (USAMRD-K), Kenya Medical Research Institute (KEMRI)/Walter Reed Project (WRP), Kisumu, Kenya
| | - Sheila Akinyi Okoth
- Malaria Branch, Division of Parasitic Diseases and Malaria, Center for Global Health, Centers for Disease Control and Prevention, Atlanta, GA, United States; Atlanta Research and Education Foundation/VA Medical Center, Decatur, GA, United States
| | - Ben Andagalu
- Department of Emerging and Infectious Diseases (DEID), United States Army Medical Research Directorate-Kenya (USAMRD-K), Kenya Medical Research Institute (KEMRI)/Walter Reed Project (WRP), Kisumu, Kenya
| | - Edwin Kamau
- Department of Emerging and Infectious Diseases (DEID), United States Army Medical Research Directorate-Kenya (USAMRD-K), Kenya Medical Research Institute (KEMRI)/Walter Reed Project (WRP), Kisumu, Kenya.
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Read AF, Huijben S. Evolutionary biology and the avoidance of antimicrobial resistance. Evol Appl 2015; 2:40-51. [PMID: 25567846 PMCID: PMC3352414 DOI: 10.1111/j.1752-4571.2008.00066.x] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2008] [Accepted: 12/11/2008] [Indexed: 11/29/2022] Open
Abstract
Evolutionary biologists have largely left the search for solutions to the drug resistance crisis to biomedical scientists, physicians, veterinarians and public health specialists. We believe this is because the vast majority of professional evolutionary biologists consider the evolutionary science of drug resistance to be conceptually uninteresting. Using malaria as case study, we argue that it is not. We review examples of evolutionary thinking that challenge various fallacies dominating antimalarial therapy, and discuss open problems that need evolutionary insight. These problems are unlikely to be resolved by biomedical scientists ungrounded in evolutionary biology. Involvement by evolutionary biologists in the science of drug resistance requires no intellectual compromises: the problems are as conceptually challenging as they are important.
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Affiliation(s)
- Andrew F Read
- Center for Infectious Disease Dynamics, Departments of Biology and Entomology, Pennsylvania State University, University Park PA, USA
| | - Silvie Huijben
- Center for Infectious Disease Dynamics, Departments of Biology and Entomology, Pennsylvania State University, University Park PA, USA ; School of Biological Sciences, University of Edinburgh West Mains Road, Edinburgh, UK
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Teboh-Ewungkem MI, Mohammed-Awel J, Baliraine FN, Duke-Sylvester SM. The effect of intermittent preventive treatment on anti-malarial drug resistance spread in areas with population movement. Malar J 2014; 13:428. [PMID: 25398463 PMCID: PMC4289180 DOI: 10.1186/1475-2875-13-428] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2014] [Accepted: 10/25/2014] [Indexed: 11/30/2022] Open
Abstract
Background The use of intermittent preventive treatment in pregnant women (IPTp), children (IPTc) and infant (IPTi) is an increasingly popular preventive strategy aimed at reducing malaria risk in these vulnerable groups. Studies to understand how this preventive intervention can affect the spread of anti-malarial drug resistance are important especially when there is human movement between neighbouring low and high transmission areas. Because the same drug is sometimes utilized for IPTi and for symptomatic malaria treatment, distinguishing their individual roles on accelerating the spread of drug resistant malaria, with or without human movement, may be difficult to isolate experimentally or by analysing data. A theoretical framework, as presented here, is thus relevant as the role of IPTi on accelerating the spread of drug resistance can be isolated in individual populations and when the populations are interconnected and interact. Methods A previously published model is expanded to include human movement between neighbouring high and low transmission areas, with focus placed on the malaria parasites. Parasite fitness functions, determined by how many humans the parasites can infect, are used to investigate how fast resistance can spread within the neighbouring communities linked by movement, when the populations are at endemic equilibrium. Results Model simulations indicate that population movement results in resistance spreading fastest in high transmission areas, and the more complete the anti-malarial resistance the faster the resistant parasite will tend to spread through a population. Moreover, the demography of infection in low transmission areas tends to change to reflect the demography of high transmission areas. Additionally, when regions are strongly connected the rate of spread of partially resistant parasites (R1) relative to drug sensitive parasites (RS), and fully resistant parasites (R2) relative to partially resistant parasites (R1) tend to behave the same in both populations, as should be expected. Conclusions In fighting anti-malarial drug resistance, different drug resistance monitoring and management policies are needed when the area in question is an isolated high or low transmission area, or when it is close and interacting with a neighbouring high or low transmission area, with human movement between them. Electronic supplementary material The online version of this article (doi:10.1186/1475-2875-13-428) contains supplementary material, which is available to authorized users.
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Zhao R, Mohammed-Awel J. A mathematical model studying mosquito-stage transmission-blocking vaccines. MATHEMATICAL BIOSCIENCES AND ENGINEERING : MBE 2014; 11:1229-1245. [PMID: 25347811 DOI: 10.3934/mbe.2014.11.1229] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
A compartmental deterministic model is proposed to evaluate the effectiveness of transmission-blocking vaccines of malaria, which targets at the parasite stage in the mosquito. The model is rigorously analyzed and numerical simulations are performed. The results and implications are discussed.
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Affiliation(s)
- Ruijun Zhao
- Department of Mathematics and Statistics, Minnesota State University, Mankato, Mankaot, MN, 56001, United States.
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31
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Abdul-Ghani R, Farag HF, Allam AF, Azazy AA. Measuring resistant-genotype transmission of malaria parasites: challenges and prospects. Parasitol Res 2014; 113:1481-7. [PMID: 24562760 DOI: 10.1007/s00436-014-3789-9] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2013] [Accepted: 01/28/2014] [Indexed: 01/09/2023]
Abstract
Increased gametocytemia in infections with resistant strains of Plasmodium species and their enhanced transmissibility are a matter of concern in planning and evaluating the impact of malaria control strategies. Various studies have determined weekly gametocyte carriage in response to antimalarial drugs in clinical trials. The advent of molecular biology techniques makes it easy to detect and quantify gametocytes, the stages responsible for transmission, and to detect resistant genotypes of the parasite. With the validation of molecular markers of resistance to certain antimalarial drugs, there is a need to devise a simpler formula that could be used with these epidemiological antimalarial resistance tools. Theoretical models for transmission of resistant malaria parasites are difficult to deploy in epidemiological studies. Therefore, devising a simple formula that determines the potential resistant-genotype transmission of malaria parasites should provide further insights into understanding the spread of drug resistance. The present perspective discusses gametocytogenesis in the context of antimalarial treatment and drug resistance. It also highlights the difficulties in applying the available theoretical models of drug resistance transmission and suggests Rashad's devised formula that could perhaps be used in determining potentially transmissible resistant genotypes as well as in mapping areas with high potential risk for the transmission of drug-resistant malaria. The suggested formula makes use of the data on gametocytes and resistant genotypes of malaria parasites, detected by molecular techniques in a certain geographical area within a particular point in time, to calculate the potential risk of resistant genotype transmission.
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Affiliation(s)
- Rashad Abdul-Ghani
- Department of Parasitology, Faculty of Medicine and Health Sciences, Sana'a University, Sana'a, Yemen,
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Klein EY. The impact of heterogeneous transmission on the establishment and spread of antimalarial drug resistance. J Theor Biol 2014; 340:177-85. [PMID: 24076451 PMCID: PMC3864917 DOI: 10.1016/j.jtbi.2013.09.022] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2013] [Revised: 09/01/2013] [Accepted: 09/16/2013] [Indexed: 10/26/2022]
Abstract
Despite the important insights gained by extending the classical models of malaria, other factors, such as immunity, heterogeneous biting, and differential patterns of drug use have not been fully explored due to the complexity of modeling multiple simultaneous malaria infections competing within a host. Understanding these factors is important for understanding how to control the spread of drug resistance to artemisinin which is just emerging in Southeast Asia. The emergence of resistance plays out at the population level, but is the result of competition within individuals for transmission events. Most studies of drug resistance evolution have focused on transmission between hosts and ignored the role of within-host competition due to the inherent complexity of modeling at multiple scales. To embed within-host competition in the model, we used an agent-based framework that was developed to understand how deviations from the classical assumptions of the Ross-MacDonald type models, which have been well-described and analyzed, impact the dynamics of disease. While structured to be a stochastic analog to classical Ross-Macdonald type models, the model is nonetheless based on individuals, and thus aspects of within-host competition can be explored. We use this framework to explore the role of heterogeneous biting and transmission on the establishment and spread of resistance in a population. We find that heterogeneous transmission slows the establishment of resistance in a population, but once resistance is established, it speeds the spread of resistance through the population. These results are due to the skewed distribution of biting which makes onward transmission a low probability and suggests that targeting the "core" group of individuals that provide the vast majority of bites could significantly slow the spread of resistance.
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Affiliation(s)
- Eili Y Klein
- Center for Advanced Modeling, Department of Emergency Medicine, Johns Hopkins University, 5801 Smith Avenue, Davis Suite 3220, Baltimore, MD 21209, United States; Center for Disease Dynamics, Economics & Policy, Washington, DC, United States.
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Abdul-Ghani R, Farag HF, Allam AF, Shawky SM, Al-Mekhlafi AM. Mutant Plasmodium falciparum chloroquine resistance transporter in Hodeidah, Yemen: association with parasitologic indices and treatment-seeking behaviors. Acta Trop 2013; 128:473-8. [PMID: 23906615 DOI: 10.1016/j.actatropica.2013.07.010] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2013] [Revised: 07/04/2013] [Accepted: 07/17/2013] [Indexed: 11/27/2022]
Abstract
Malaria still represents a major health problem in Yemen, particularly in Hodeidah, despite continuing efforts to eliminate it. With the absence of clinically proven vaccines, chemotherapy with antimalarials is still greatly needed. Chloroquine (CQ) has been popular as the drug of choice for malaria control. However, Plasmodium falciparum resistance to CQ has been one of the main obstacles in malaria control and elimination. Although CQ is no longer the recommended antimalarial chemotherapy, it has remained the number one over-the-counter antimalarial drug in many endemic areas, including Yemen, and is still used for self-medication. In addition, promising reports on CQ efficacy reversal in many African countries brought it again into the scene. This has led to a growing interest in the possibility of its re-introduction, particularly with the concerns raised about the parasite resistance to artemisinin-based combination therapies. Therefore, the present study aimed at analyzing the CQ-associated pfcrt 76T mutation in P. falciparum isolates from patients with uncomplicated falciparum malaria in Hodeidah, west of Yemen. The association of treatment-seeking behaviors and antimalarial drug use with the pfcrt 76T mutant allele was also studied. It was revealed that there is still a sustained high frequency of this molecular marker among parasite isolates associated with younger age, decreased parasite density and the presence of gametocytes in blood. Delay in seeking treatment and frequent use of antimalarials were the behaviors significantly associated with the presence of the pfcrt 76T mutant allele among patients reporting a history of malaria treatment.
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Vanaerschot M, Huijben S, Van den Broeck F, Dujardin JC. Drug resistance in vectorborne parasites: multiple actors and scenarios for an evolutionary arms race. FEMS Microbiol Rev 2013; 38:41-55. [PMID: 23815683 DOI: 10.1111/1574-6976.12032] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2013] [Revised: 06/17/2013] [Accepted: 06/25/2013] [Indexed: 12/14/2022] Open
Abstract
Drug-resistant pathogens emerge faster than new drugs come out of drug discovery pipelines. Current and future drug options should therefore be better protected, requiring a clear understanding of the factors that contribute to the natural history of drug resistance. Although many of these factors are relatively well understood for most bacteria, this proves to be more complex for vectorborne parasites. In this review, we discuss considering three key models (Plasmodium, Leishmania and Schistosoma) how drug resistance can emerge, spread and persist. We demonstrate a multiplicity of scenarios, clearly resulting from the biological diversity of the different organisms, but also from the different modes of action of the drugs used, the specific within- and between-host ecology of the parasites, and environmental factors that may have direct or indirect effects. We conclude that integrated control of drug-resistant vectorborne parasites is not dependent upon chemotherapy only, but also requires a better insight into the ecology of these parasites and how their transmission can be impaired.
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Affiliation(s)
- Manu Vanaerschot
- Unit of Molecular Parasitology, Department of Biomedical Sciences, Institute of Tropical Medicine, Antwerp, Belgium
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Antimalarial drug resistance: a review of the biology and strategies to delay emergence and spread. Int J Antimicrob Agents 2013; 41:311-7. [PMID: 23394809 DOI: 10.1016/j.ijantimicag.2012.12.007] [Citation(s) in RCA: 82] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2012] [Revised: 12/12/2012] [Accepted: 12/13/2012] [Indexed: 11/21/2022]
Abstract
The emergence of resistance to former first-line antimalarial drugs has been an unmitigated disaster. In recent years, artemisinin class drugs have become standard and they are considered an essential tool for helping to eradicate the disease. However, their ability to reduce morbidity and mortality and to slow transmission requires the maintenance of effectiveness. Recently, an artemisinin delayed-clearance phenotype was described. This is believed to be the precursor to resistance and threatens local elimination and global eradication plans. Understanding how resistance emerges and spreads is important for developing strategies to contain its spread. Resistance is the result of two processes: (i) drug selection of resistant parasites; and (ii) the spread of resistance. In this review, we examine the factors that lead to both drug selection and the spread of resistance. We then examine strategies for controlling the spread of resistance, pointing out the complexities and deficiencies in predicting how resistance will spread.
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The potential elimination of Plasmodium vivax malaria by relapse treatment: insights from a transmission model and surveillance data from NW India. PLoS Negl Trop Dis 2013; 7:e1979. [PMID: 23326611 PMCID: PMC3542148 DOI: 10.1371/journal.pntd.0001979] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2012] [Accepted: 11/04/2012] [Indexed: 12/04/2022] Open
Abstract
Background With over a hundred million annual infections and rising morbidity and mortality, Plasmodium vivax malaria remains largely a neglected disease. In particular, the dependence of this malaria species on relapses and the potential significance of the dormant stage as a therapeutic target, are poorly understood. Methodology/Principal Findings To quantify relapse parameters and assess the population-wide consequences of anti-relapse treatment, we formulated a transmission model for P. vivax suitable for parameter inference with a recently developed statistical method based on routine surveillance data. A low-endemic region in NW India, whose strong seasonality demarcates the transmission season, provides an opportunity to apply this modeling approach. Our model gives maximum likelihood estimates of 7.1 months for the mean latency and 31% for the relapse rate, in close agreement with regression estimates and clinical evaluation studies in the area. With a baseline of prevailing treatment practices, the model predicts that an effective anti-relapse treatment of 65% of those infected would result in elimination within a decade, and that periodic mass treatment would dramatically reduce the burden of the disease in a few years. Conclusion/Significance The striking dependence of P. vivax on relapses for survival reinforces the urgency to develop more effective anti-relapse treatments to replace Primaquine (PQ), the only available drug for the last fifty years. Our methods can provide alternative and simple means to estimate latency times and relapse frequency using routine epidemiological data, and to evaluate the population-wide impact of relapse treatment in areas similar to our study area. Plasmodium vivax, one of the four species responsible for malaria in humans, represents today a much larger global public health problem than previously recognized. The neglect of P. vivax is still apparent in the limited efforts made so far to understand the regional dynamics of the disease, and in the non-existence of practical models to guide and evaluate control measures. One main impediment is the overall uncertainty in the dynamic role of the hidden reservoir, resulting from the liver stage known as hypnozoites and responsible for relapses, a characteristic feature of this species. Current control efforts and elimination plans are therefore hampered in their ability to quantify the impact of effective anti-relapse treatments. This paper applies a P. vivax transmission model to surveillance data from a semi-arid region (in NW India), whose clear demarcation of the transmission and relapse seasons makes it especially suited for estimating relapse parameters such as frequency and rate. The model results quantify the striking dependence of P. vivax on relapses for its survival, supporting the feasibility of regional elimination and lending support to the expressed urgency of replacing Primaquine, the anti- relapse drug now in use for over fifty years with unsatisfactory efficacy, resistance and side-effects.
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Klein EY, Smith DL, Laxminarayan R, Levin S. Superinfection and the evolution of resistance to antimalarial drugs. Proc Biol Sci 2012; 279:3834-42. [PMID: 22787024 DOI: 10.1098/rspb.2012.1064] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
A major issue in the control of malaria is the evolution of drug resistance. Ecological theory has demonstrated that pathogen superinfection and the resulting within-host competition influences the evolution of specific traits. Individuals infected with Plasmodium falciparum are consistently infected by multiple parasites; however, while this probably alters the dynamics of resistance evolution, there are few robust mathematical models examining this issue. We developed a general theory for modelling the evolution of resistance with host superinfection and examine: (i) the effect of transmission intensity on the rate of resistance evolution; (ii) the importance of different biological costs of resistance; and (iii) the best measure of the frequency of resistance. We find that within-host competition retards the ability and slows the rate at which drug-resistant parasites invade, particularly as the transmission rate increases. We also find that biological costs of resistance that reduce transmission are less important than reductions in the duration of drug-resistant infections. Lastly, we find that random sampling of the population for resistant parasites is likely to significantly underestimate the frequency of resistance. Considering superinfection in mathematical models of antimalarial drug resistance may thus be important for generating accurate predictions of interventions to contain resistance.
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Affiliation(s)
- Eili Y Klein
- Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544, USA.
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Mallick PK, Joshi H, Valecha N, Sharma SK, Eapen A, Bhatt RM, Srivastava HC, Sutton PL, Dash AP, Bhasin VK. Mutant pfcrt "SVMNT" haplotype and wild type pfmdr1 "N86" are endemic in Plasmodium vivax dominated areas of India under high chloroquine exposure. Malar J 2012; 11:16. [PMID: 22236376 PMCID: PMC3283508 DOI: 10.1186/1475-2875-11-16] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2011] [Accepted: 01/11/2012] [Indexed: 11/23/2022] Open
Abstract
Background Chloroquine resistance (CQR) phenotype in Plasmodium falciparum is associated with mutations in pfcrt and pfmdr-1 genes. Mutations at amino acid position 72-76 of pfcrt gene, here defined as pfcrt haplotype are associated with the geographic origin of chloroquine resistant parasite. Here, mutations at 72-76 and codon 220 of pfcrt gene and N86Y pfmdr-1 mutation were studied in blood samples collected across 11 field sites, inclusive of high and low P. falciparum prevalent areas in India. Any probable correlation between these mutations and clinical outcome of CQ treatment was also investigated. Methods Finger pricked blood spotted on Whatman No.3 papers were collected from falciparum malaria patients of high and low P. falciparum prevalent areas. For pfcrt haplotype investigation, the parasite DNA was extracted from blood samples and used for PCR amplification, followed by partial sequencing of the pfcrt gene. For pfmdr-1 N86Y mutation, the PCR product was subjected to restriction digestion with AflIII endonuclease enzyme. Results In 240 P. falciparum isolates with reported in vivo CQ therapeutic efficacy, the analysis of mutations in pfcrt gene shows that mutant SVMNT-S (67.50%) and CVIET-S (23.75%) occurred irrespective of clinical outcome and wild type CVMNK-A (7.91%) occurred only in adequate clinical and parasitological response samples. Of 287 P. falciparum isolates, SVMNTS 192 (66.89%) prevailed in all study sites and showed almost monomorphic existence (98.42% isolates) in low P. falciparum prevalent areas. However, CVIETS-S (19.51%) and CVMNK-A (11.84%) occurrence was limited to high P. falciparum prevalent areas. Investigation of pfmdr-1 N86Y mutation shows no correlation with clinical outcomes. The wild type N86 was prevalent in all the low P. falciparum prevalent areas (94.48%). However, mutant N86Y was comparably higher in numbers at the high P. falciparum prevalent areas (42.76%). Conclusions The wild type pfcrt gene is linked to chloroquine sensitivity; however, presence of mutation cannot explain the therapeutic efficacy of CQ in the current scenario of chloroquine resistance. The monomorphic existence of mutant SVMNT haplotype, infer inbreeding and faster spread of CQR parasite in areas with higher P. vivax prevalance and chloroquine exposure, whereas, diversity is maintained in pfcrt gene at high P. falciparum prevalent areas.
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Paganotti GM, Gallo BC, Verra F, Sirima BS, Nebie I, Diarra A, Coluzzi M, Modiano D. Human Genetic Variation Is Associated With Plasmodium falciparum Drug Resistance. J Infect Dis 2011; 204:1772-8. [DOI: 10.1093/infdis/jir629] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
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Tsumori Y, Ndounga M, Sunahara T, Hayashida N, Inoue M, Nakazawa S, Casimiro P, Isozumi R, Uemura H, Tanabe K, Kaneko O, Culleton R. Plasmodium falciparum: differential selection of drug resistance alleles in contiguous urban and peri-urban areas of Brazzaville, Republic of Congo. PLoS One 2011; 6:e23430. [PMID: 21858115 PMCID: PMC3156131 DOI: 10.1371/journal.pone.0023430] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2011] [Accepted: 07/16/2011] [Indexed: 12/25/2022] Open
Abstract
The African continent is currently experiencing rapid population growth, with rising urbanization increasing the percentage of the population living in large towns and cities. We studied the impact of the degree of urbanization on the population genetics of Plasmodium falciparum in urban and peri-urban areas in and around the city of Brazzaville, Republic of Congo. This field setting, which incorporates local health centers situated in areas of varying urbanization, is of interest as it allows the characterization of malaria parasites from areas where the human, parasite, and mosquito populations are shared, but where differences in the degree of urbanization (leading to dramatic differences in transmission intensity) cause the pattern of malaria transmission to differ greatly. We have investigated how these differences in transmission intensity affect parasite genetic diversity, including the amount of genetic polymorphism in each area, the degree of linkage disequilibrium within the populations, and the prevalence and frequency of drug resistance markers. To determine parasite population structure, heterozygosity and linkage disequilibrium, we typed eight microsatellite markers and performed haplotype analysis of the msp1 gene by PCR. Mutations known to be associated with resistance to the antimalarial drugs chloroquine and pyrimethamine were determined by sequencing the relevant portions of the crt and dhfr genes, respectively. We found that parasite genetic diversity was comparable between the two sites, with high levels of polymorphism being maintained in both areas despite dramatic differences in transmission intensity. Crucially, we found that the frequencies of genetic markers of drug resistance against pyrimethamine and chloroquine differed significantly between the sites, indicative of differing selection pressures in the two areas.
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Affiliation(s)
- Yoko Tsumori
- Department of Protozoology, Institute of Tropical Medicine (NEKKEN), and the Global COE Program, Nagasaki University, Nagasaki, Japan
| | - Mathieu Ndounga
- Centre d’Etudes des Resources Vegetales, Brazzaville, Republic of Congo
| | - Toshihiko Sunahara
- Department of International Health, Institute of Tropical Medicine (NEKKEN), Nagasaki University, Nagasaki, Japan
| | - Nozomi Hayashida
- Department of Protozoology, Institute of Tropical Medicine (NEKKEN), and the Global COE Program, Nagasaki University, Nagasaki, Japan
| | - Megumi Inoue
- Department of Protozoology, Institute of Tropical Medicine (NEKKEN), and the Global COE Program, Nagasaki University, Nagasaki, Japan
| | - Shusuke Nakazawa
- Department of Protozoology, Institute of Tropical Medicine (NEKKEN), and the Global COE Program, Nagasaki University, Nagasaki, Japan
| | - Prisca Casimiro
- Centre d’Etudes des Resources Vegetales, Brazzaville, Republic of Congo
| | - Rie Isozumi
- Department of Protozoology, Institute of Tropical Medicine (NEKKEN), and the Global COE Program, Nagasaki University, Nagasaki, Japan
| | - Haruki Uemura
- Department of Protozoology, Institute of Tropical Medicine (NEKKEN), and the Global COE Program, Nagasaki University, Nagasaki, Japan
| | - Kazuyuki Tanabe
- Laboratory of Malariology, International Research Centre of Infectious Diseases, Research Institute of Microbial Diseases, Osaka University, Osaka, Japan
| | - Osamu Kaneko
- Department of Protozoology, Institute of Tropical Medicine (NEKKEN), and the Global COE Program, Nagasaki University, Nagasaki, Japan
| | - Richard Culleton
- Department of Protozoology, Institute of Tropical Medicine (NEKKEN), and the Global COE Program, Nagasaki University, Nagasaki, Japan
- Laboratory of Malariology, International Research Centre of Infectious Diseases, Research Institute of Microbial Diseases, Osaka University, Osaka, Japan
- Malaria Unit, Institute of Tropical Medicine (NEKKEN), Nagasaki University, Nagasaki, Japan
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Bhadra A, Ionides EL, Laneri K, Pascual M, Bouma M, Dhiman RC. Malaria in Northwest India: Data Analysis via Partially Observed Stochastic Differential Equation Models Driven by Lévy Noise. J Am Stat Assoc 2011. [DOI: 10.1198/jasa.2011.ap10323] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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zur Wiesch PA, Kouyos R, Engelstädter J, Regoes RR, Bonhoeffer S. Population biological principles of drug-resistance evolution in infectious diseases. THE LANCET. INFECTIOUS DISEASES 2011; 11:236-47. [PMID: 21371657 DOI: 10.1016/s1473-3099(10)70264-4] [Citation(s) in RCA: 161] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
The emergence of resistant pathogens in response to selection pressure by drugs and their possible disappearance when drug use is discontinued are evolutionary processes common to many pathogens. Population biological models have been used to study the dynamics of resistance in viruses, bacteria, and eukaryotic microparasites both at the level of the individual treated host and of the treated host population. Despite the existence of generic features that underlie such evolutionary dynamics, different conclusions have been reached about the key factors affecting the rate of resistance evolution and how to best use drugs to minimise the risk of generating high levels of resistance. Improved understanding of generic versus specific population biological aspects will help to translate results between different studies, and allow development of a more rational basis for sustainable drug use than exists at present.
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Affiliation(s)
- Pia Abel zur Wiesch
- Integrative Biology, Swiss Federal Institute of Technology, Zurich, Switzerland
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Alonso D, Bouma MJ, Pascual M. Epidemic malaria and warmer temperatures in recent decades in an East African highland. Proc Biol Sci 2010; 278:1661-9. [PMID: 21068045 PMCID: PMC3081772 DOI: 10.1098/rspb.2010.2020] [Citation(s) in RCA: 90] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
Climate change impacts on malaria are typically assessed with scenarios for the long-term future. Here we focus instead on the recent past (1970–2003) to address whether warmer temperatures have already increased the incidence of malaria in a highland region of East Africa. Our analyses rely on a new coupled mosquito–human model of malaria, which we use to compare projected disease levels with and without the observed temperature trend. Predicted malaria cases exhibit a highly nonlinear response to warming, with a significant increase from the 1970s to the 1990s, although typical epidemic sizes are below those observed. These findings suggest that climate change has already played an important role in the exacerbation of malaria in this region. As the observed changes in malaria are even larger than those predicted by our model, other factors previously suggested to explain all of the increase in malaria may be enhancing the impact of climate change.
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Affiliation(s)
- David Alonso
- University of Groningen, CEES, Haren, The Netherlands
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Artzy-Randrup Y, Alonso D, Pascual M. Transmission intensity and drug resistance in malaria population dynamics: implications for climate change. PLoS One 2010; 5:e13588. [PMID: 21060886 PMCID: PMC2965653 DOI: 10.1371/journal.pone.0013588] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2010] [Accepted: 08/02/2010] [Indexed: 11/30/2022] Open
Abstract
Although the spread of drug resistance and the influence of climate change on malaria are most often considered separately, these factors have the potential to interact through altered levels of transmission intensity. The influence of transmission intensity on the evolution of drug resistance has been addressed in theoretical studies from a population genetics' perspective; less is known however on how epidemiological dynamics at the population level modulates this influence. We ask from a theoretical perspective, whether population dynamics can explain non-trivial, non-monotonic, patterns of treatment failure with transmission intensity, and, if so, under what conditions. We then address the implications of warmer temperatures in an East African highland, where, as in other similar regions at the altitudinal edge of malaria's distribution, there has been a pronounced increase of cases from the 1970s to the 1990s. Our theoretical analyses, with a transmission model that includes different levels of immunity, demonstrate that an increase in transmission beyond a threshold can lead to a decrease in drug resistance, as previously shown [1], but that a second threshold may occur and lead to the re-establishment of drug resistance. Estimates of the increase in transmission intensity from the 1970s to the 1990s for the Kenyan time series, obtained by fitting the two-stage version of the model with an explicit representation of vector dynamics, suggest that warmer temperatures are likely to have moved the system towards the first threshold, and in so doing, to have promoted the faster spread of drug resistance. Climate change and drug resistance can interact and need not be considered as alternative explanations for trends in disease incidence in this region. Non-monotonic patterns of treatment failure with transmission intensity similar to those described as the ‘valley phenomenon’ for Uganda can result from epidemiological dynamics but under poorly understood assumptions.
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Affiliation(s)
- Yael Artzy-Randrup
- Howard Hughes Medical Institute, Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, Michigan, United States of America.
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Forcing versus feedback: epidemic malaria and monsoon rains in northwest India. PLoS Comput Biol 2010; 6:e1000898. [PMID: 20824122 PMCID: PMC2932675 DOI: 10.1371/journal.pcbi.1000898] [Citation(s) in RCA: 102] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2010] [Accepted: 07/21/2010] [Indexed: 11/19/2022] Open
Abstract
Malaria epidemics in regions with seasonal windows of transmission can vary greatly in size from year to year. A central question has been whether these interannual cycles are driven by climate, are instead generated by the intrinsic dynamics of the disease, or result from the resonance of these two mechanisms. This corresponds to the more general inverse problem of identifying the respective roles of external forcings vs. internal feedbacks from time series for nonlinear and noisy systems. We propose here a quantitative approach to formally compare rival hypotheses on climate vs. disease dynamics, or external forcings vs. internal feedbacks, that combines dynamical models with recently developed, computational inference methods. The interannual patterns of epidemic malaria are investigated here for desert regions of northwest India, with extensive epidemiological records for Plasmodium falciparum malaria for the past two decades. We formulate a dynamical model of malaria transmission that explicitly incorporates rainfall, and we rely on recent advances on parameter estimation for nonlinear and stochastic dynamical systems based on sequential Monte Carlo methods. Results show a significant effect of rainfall in the inter-annual variability of epidemic malaria that involves a threshold in the disease response. The model exhibits high prediction skill for yearly cases in the malaria transmission season following the monsoonal rains. Consideration of a more complex model with clinical immunity demonstrates the robustness of the findings and suggests a role of infected individuals that lack clinical symptoms as a reservoir for transmission. Our results indicate that the nonlinear dynamics of the disease itself play a role at the seasonal, but not the interannual, time scales. They illustrate the feasibility of forecasting malaria epidemics in desert and semi-arid regions of India based on climate variability. This approach should be applicable to malaria in other locations, to other infectious diseases, and to other nonlinear systems under forcing. Malaria epidemics can exhibit pronounced variation from year to year that can be driven by external forcings, such as climate, or can be generated instead by dynamic feedbacks within the disease system itself. For example, levels of immunity in the population (or control efforts) can rise and fall as the result of past levels of infection. This type of feedback is found in the dynamics of all (nonlinear) biological systems. Feedbacks can interact in complex ways with external drivers, for example by creating refractory periods. It remains a challenge to identify internal feedbacks vs. external forcings from available temporal records of aggregated reported cases and forcing variables. We propose a quantitative approach that can statistically compare the hypotheses of feedbacks vs. forcings (epidemiological vs. climate) based on dynamical and mechanistic models. Our approach is computational, based on a large number of computer simulations of the different models. We illustrate and apply the approach to the analysis of extensive monthly records for malaria incidence in desert regions of India that span two decades. Our analyses confirm the strong role of rainfall, and quantify this effect with transmission model(s) for malaria that include rainfall and are shown to exhibit a remarkable prediction skill.
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Progress in modelling malaria transmission. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010; 673:1-12. [PMID: 20632526 DOI: 10.1007/978-1-4419-6064-1_1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/05/2023]
Abstract
Transmission of human malaria is a complicated dynamic process that involves populations of humans, parasites, and vectors. The first mathematical models of malaria are now more than a century old, and they are still a useful conceptual synthetic description of transmission, but they fail in some important ways. To address some of those failures, malaria transmission models have now been extended to consider malaria immunity, superinfection, and heterogeneous biting, among other factors. These extensions of the basic theory often arise from field studies in a single place, but tests of the theory come comparing standard measures of malaria taken from many places across the transmission spectrum. Several good models now exist that describe these basic patterns across the spectrum from low to high endemicity. The future of malaria modeling will involve applying these models to make decisions about real systems and finding new ways to test the underlying causes of the patterns.
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Chaves LF, Kaneko A, Pascual M. Random, top-down, or bottom-up coexistence of parasites: malaria population dynamics in multi-parasitic settings. Ecology 2009; 90:2414-25. [PMID: 19769120 DOI: 10.1890/08-1022.1] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Epidemiological models concerned with the control of malaria using interventions such as bed nets and vaccines increasingly incorporate realistic aspects of malaria biology. The increasing complexity of these models limits their ability to abstract ecological processes and to address questions on the regulation of population dynamics using time-series data, particularly in regards to interactions between different pathogens and the regulatory role of innate (bottom-up) and acquired (top-down) immunity. We use a theoretical framework to test hypotheses on the importance of population-level immunity and parasite abundance in regulating the population dynamics of malaria. We use qualitative loop analyses to examine the sign of the interaction between Plasmodium falciparum and P. vivax at the population level, and we discuss implications of this sign for the within-host regulation of parasites. Our analyses of monthly malaria time-series data from the island of Espirito Santo, Vanuatu (1983-1997), show that the dynamics of P. falciparum are not sensitive to P. vivax, whereas infections by the latter increase in response to those of the former. These results support a differential use of resources inside the hosts, a resource-consumer interaction between hosts and their immune system, and within-host regulation of parasites. Finally, our results emphasize the need to better understand factors regulating malaria dynamics before developing control strategies and call for the use of control strategies directed at the interruption of transmission, such as vector control and the use of bed nets.
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Affiliation(s)
- Luis Fernando Chaves
- Department of Ecology and Evolutionary Biology, The University of Michigan, Ann Arbor, Michigan 48109-1048, USA.
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Mmbando BP, Lusingu JP, Vestergaard LS, Lemnge MM, Theander TG, Scheike TH. Parasite threshold associated with clinical malaria in areas of different transmission intensities in north eastern Tanzania. BMC Med Res Methodol 2009; 9:75. [PMID: 19909523 PMCID: PMC2781814 DOI: 10.1186/1471-2288-9-75] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2009] [Accepted: 11/12/2009] [Indexed: 11/21/2022] Open
Abstract
Background In Sub-Sahara Africa, malaria due to Plasmodium falciparum is the main cause of ill health. Evaluation of malaria interventions, such as drugs and vaccines depends on clinical definition of the disease, which is still a challenge due to lack of distinct malaria specific clinical features. Parasite threshold is used in definition of clinical malaria in evaluation of interventions. This however, is likely to be influenced by other factors such as transmission intensity as well as individual level of immunity against malaria. Methods This paper describes step function and dose response model with threshold parameter as a tool for estimation of parasite threshold for onset of malaria fever in highlands (low transmission) and lowlands (high transmission intensity) strata. These models were fitted using logistic regression stratified by strata and age groups (0-1, 2-3, 4-5, 6-9, and 10-19 years). Dose response model was further extended to fit all age groups combined in each stratum. Sub-sampling bootstrap was used to compute confidence intervals. Cross-sectional and passive case detection data from Korogwe district, north eastern Tanzania were used. Results Dose response model was better in the estimation of parasite thresholds. Parasite thresholds (scale = log parasite/μL) were high in lowlands than in highlands. In the lowlands, children in age group 4-5 years had the highest parasite threshold (8.73) while individuals aged 10-19 years had the lowest (6.81). In the highlands, children aged 0-1 years had the highest threshold (7.12) and those aged 10-19 years had the lowest (4.62). Regression analysis with all ages combined showed similar pattern of thresholds in both strata, whereby, in the lowlands the threshold was highest in age group 2-5 years and lowest in older individuals, while in the highlands was highest in age group 0-1 and decreased with increased age. The sensitivity of parasite threshold by age group ranged from 64%-74% in the lowlands and 67%-97% in the highlands; while specificity ranged between 67%-90% in the lowlands and 37%-73% in the highlands. Conclusion Dose response model with threshold parameter can be used to estimate parasite threshold associated with malaria fever onset. Parasite threshold were lower in older individuals and in low malaria transmission area.
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Affiliation(s)
- Bruno P Mmbando
- Department of Biostatistics, University of Copenhagen, Copenhagen, Denmark.
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Eastman RT, Fidock DA. Artemisinin-based combination therapies: a vital tool in efforts to eliminate malaria. Nat Rev Microbiol 2009; 7:864-74. [PMID: 19881520 DOI: 10.1038/nrmicro2239] [Citation(s) in RCA: 369] [Impact Index Per Article: 24.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Plasmodium falciparum resistance to chloroquine and sulphadoxine-pyrimethamine has led to the recent adoption of artemisinin-based combination therapies (ACTs) as the first line of treatment against malaria. ACTs comprise semisynthetic artemisinin derivatives paired with distinct chemical classes of longer acting drugs. These artemisinins are exceptionally potent against the pathogenic asexual blood stages of Plasmodium parasites and also act on the transmissible sexual stages. These combinations increase the rates of clinical and parasitological cures and decrease the selection pressure for the emergence of antimalarial resistance. This Review article discusses our current knowledge about the mode of action of ACTs, their pharmacological properties and the proposed mechanisms of drug resistance.
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Affiliation(s)
- Richard T Eastman
- Department of Microbiology & Immunology, Columbia University College of Physicians and Surgeons, Hammer Health Sciences Center, Room 1502, 701 West 168th Street, New York 10032, New York, USA.
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Escalante AA, Smith DL, Kim Y. The dynamics of mutations associated with anti-malarial drug resistance in Plasmodium falciparum. Trends Parasitol 2009; 25:557-63. [PMID: 19864183 DOI: 10.1016/j.pt.2009.09.008] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2009] [Revised: 07/22/2009] [Accepted: 09/10/2009] [Indexed: 10/20/2022]
Abstract
The evolution of resistance in Plasmodium falciparum against safe and affordable drugs such as chloroquine (CQ) and sulfadoxine-pyrimethamine (SP) is a major global health threat. Investigating the dynamics of resistance against these antimalarial drugs will lead to approaches for addressing the problem of resistance in malarial parasites that are solidly based in evolutionary genetics and population biology. In this article, we discuss current developments in population biology modeling and evolutionary genetics. Despite great advancements achieved in the past decade, understanding the complex dynamics of mutations conferring drug resistance in P. falciparum requires approaches that consider the parasite population structure among other demographic processes.
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Affiliation(s)
- Ananias A Escalante
- School of Life Sciences, Arizona State University, PO Box 874501, Tempe, AZ 85287-4501, USA.
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