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Dekel E, Rivkin A, Heidenreich M, Nadav Y, Ofir-Birin Y, Porat Z, Regev-Rudzki N. Identification and classification of the malaria parasite blood developmental stages, using imaging flow cytometry. Methods 2016; 112:157-166. [PMID: 27350362 DOI: 10.1016/j.ymeth.2016.06.021] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2016] [Revised: 06/02/2016] [Accepted: 06/22/2016] [Indexed: 10/21/2022] Open
Abstract
Malaria is the most devastating parasitic disease of humans, caused by the unicellular protozoa of the Plasmodium genus, such as Plasmodium falciparum (Pf) and is responsible for up to a million deaths each year. Pf life cycle is complex, with transmission of the parasite between humans via mosquitos involving a remarkable series of morphological transformations. In the bloodstream, the parasites undergo asexual multiplications inside the red blood cell (RBC), where they mature through the ring (R), trophozoite (T) and schizont (S) stages, and sexual development, resulting in gametocytes (G). All symptoms of malaria pathology are caused by the asexual blood stage parasites. Flow cytometry methods were previously used to detect malaria infected (i) RBCs, in live or fixed cells, using DNA (Hoechst) and RNA (Thiazole Orange) stains. Here, by using imaging flow cytometry, we developed improved methods of identifying and quantifying each of the four parasite blood stages (R, T, S and G). This technique allows multi-channel, high resolution imaging of individual parasites, as well as detailed morphological quantification of Pf-iRBCs cultures. Moreover, by measuring iRBC morphological properties, we can eliminate corrupted and extracellular (dying) parasites from the analysis, providing accurate quantification and robust measurement of the parasitemia profile. This new method is a valuable tool in malaria molecular biology research and drug screen assays.
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Affiliation(s)
- Elya Dekel
- Faculty of Biochemistry, Department of Biomolecular Sciences, Weizmann Institute of Science, Rehovot, Israel
| | - Anna Rivkin
- Faculty of Biochemistry, Department of Biomolecular Sciences, Weizmann Institute of Science, Rehovot, Israel
| | - Meta Heidenreich
- Faculty of Biochemistry, Department of Biomolecular Sciences, Weizmann Institute of Science, Rehovot, Israel
| | - Yotam Nadav
- Faculty of Biochemistry, Department of Biomolecular Sciences, Weizmann Institute of Science, Rehovot, Israel
| | - Yifat Ofir-Birin
- Faculty of Biochemistry, Department of Biomolecular Sciences, Weizmann Institute of Science, Rehovot, Israel
| | - Ziv Porat
- Flow Cytometry Unit, Biological Services Department, Weizmann Institute of Science, Rehovot, Israel.
| | - Neta Regev-Rudzki
- Faculty of Biochemistry, Department of Biomolecular Sciences, Weizmann Institute of Science, Rehovot, Israel.
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Traoré K, Arama C, Médebielle M, Doumbo O, Picot S. Do advanced glycation end-products play a role in malaria susceptibility? ACTA ACUST UNITED AC 2016; 23:15. [PMID: 27012162 PMCID: PMC4807375 DOI: 10.1051/parasite/2016015] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2015] [Accepted: 03/10/2016] [Indexed: 12/30/2022]
Abstract
There are growing data supporting the differences in susceptibility to malaria described between sympatric populations with different lifestyles. Evidence has also been growing for some time that nutritional status and the host's metabolism are part of the complex mechanisms underlying these differences. The role of dietary advanced glycation end-products (AGEs) in the modulation of immune responses (innate and adaptive responses) and chronic oxidative stress has been established. But less is known about AGE implication in naturally acquired immunity and susceptibility to malaria. Since inflammatory immune responses and oxidative events have been demonstrated as the hallmark of malaria infection, it seems crucial to investigate the role of AGE in susceptibility or resistance to malaria. This review provides new insight into the relationship between nutrition, metabolic disorders, and infections, and how this may influence the mechanisms of susceptibility or resistance to malaria in endemic areas.
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Affiliation(s)
- Karim Traoré
- Malaria Research and Training Center MRTC-DEAP-FMPOS-UMI 3189, Université des Sciences, des Techniques et des Technologies de Bamako, BP 1805, Bamako, Mali - Univ Lyon, Université Claude Bernard Lyon 1, Institut de Chimie, de Biologie Moléculaire et Supramoléculaire ICBMS-UMR5246, CNRS-INSA-CPE, Malaria Research Unit, - 43 boulevard du 11 novembre 1918, 69622 Lyon, France
| | - Charles Arama
- Malaria Research and Training Center MRTC-DEAP-FMPOS-UMI 3189, Université des Sciences, des Techniques et des Technologies de Bamako, BP 1805, Bamako, Mali
| | - Maurice Médebielle
- Univ Lyon, Université Claude Bernard Lyon 1, Institut de Chimie, de Biologie Moléculaire et Supramoléculaire ICBMS-UMR5246, CNRS-INSA-CPE, - 43 boulevard du 11 novembre 1918, 69622 Lyon, France
| | - Ogobara Doumbo
- Malaria Research and Training Center MRTC-DEAP-FMPOS-UMI 3189, Université des Sciences, des Techniques et des Technologies de Bamako, BP 1805, Bamako, Mali
| | - Stéphane Picot
- Univ Lyon, Université Claude Bernard Lyon 1, Institut de Chimie, de Biologie Moléculaire et Supramoléculaire ICBMS-UMR5246, CNRS-INSA-CPE, Malaria Research Unit, - 43 boulevard du 11 novembre 1918, 69622 Lyon, France
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53
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Quantifying Transmission Investment in Malaria Parasites. PLoS Comput Biol 2016; 12:e1004718. [PMID: 26890485 PMCID: PMC4759450 DOI: 10.1371/journal.pcbi.1004718] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2015] [Accepted: 12/17/2015] [Indexed: 01/27/2023] Open
Abstract
Many microparasites infect new hosts with specialized life stages, requiring a subset of the parasite population to forgo proliferation and develop into transmission forms. Transmission stage production influences infectivity, host exploitation, and the impact of medical interventions like drug treatment. Predicting how parasites will respond to public health efforts on both epidemiological and evolutionary timescales requires understanding transmission strategies. These strategies can rarely be observed directly and must typically be inferred from infection dynamics. Using malaria as a case study, we test previously described methods for inferring transmission stage investment against simulated data generated with a model of within-host infection dynamics, where the true transmission investment is known. We show that existing methods are inadequate and potentially very misleading. The key difficulty lies in separating transmission stages produced by different generations of parasites. We develop a new approach that performs much better on simulated data. Applying this approach to real data from mice infected with a single Plasmodium chabaudi strain, we estimate that transmission investment varies from zero to 20%, with evidence for variable investment over time in some hosts, but not others. These patterns suggest that, even in experimental infections where host genetics and other environmental factors are controlled, parasites may exhibit remarkably different patterns of transmission investment. Malaria parasites are carried from host to host by blood-feeding insects, a process that requires some portion of the parasite population to develop into transmission forms that cannot replicate within the current host. The fraction of parasites specialized for transmission instead of replication (transmission investment) could change with each cycle of replication in response to changing conditions within the host. Measuring how transmission investment changes through time could help us understand how malaria spreads so efficiently through populations of human and other animals. However, transmission investment is usually impossible to measure directly and instead has to be estimated by comparing the number of transmission forms with total parasite numbers in blood samples. Here we use a model to simulate data from an infection—so that the true level of transmission investment is known—and test published methods for estimation. We find that existing methods do not accurately estimate transmission investment from simulated data, and we propose a new statistical method that works substantially better. When applied to rodent malaria data, our method suggests that transmission investment can vary substantially over the course of infection, with notably different patterns of allocation across hosts.
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Abstract
Mathematical modelling provides an effective way to challenge conventional wisdom about
parasite evolution and investigate why parasites ‘do what they do’ within the host. Models
can reveal when intuition cannot explain observed patterns, when more complicated biology
must be considered, and when experimental and statistical methods are likely to mislead.
We describe how models of within-host infection dynamics can refine experimental design,
and focus on the case study of malaria to highlight how integration between models and
data can guide understanding of parasite fitness in three areas: (1) the adaptive
significance of chronic infections; (2) the potential for tradeoffs between virulence and
transmission; and (3) the implications of within-vector dynamics. We emphasize that models
are often useful when they highlight unexpected patterns in parasite evolution, revealing
instead why intuition yields the wrong answer and what combination of theory and data are
needed to advance understanding.
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Pigeault R, Vézilier J, Cornet S, Zélé F, Nicot A, Perret P, Gandon S, Rivero A. Avian malaria: a new lease of life for an old experimental model to study the evolutionary ecology of Plasmodium. Philos Trans R Soc Lond B Biol Sci 2015; 370:20140300. [PMID: 26150666 PMCID: PMC4528498 DOI: 10.1098/rstb.2014.0300] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/27/2015] [Indexed: 08/13/2023] Open
Abstract
Avian malaria has historically played an important role as a model in the study of human malaria, being a stimulus for the development of medical parasitology. Avian malaria has recently come back to the research scene as a unique animal model to understand the ecology and evolution of the disease, both in the field and in the laboratory. Avian malaria is highly prevalent in birds and mosquitoes around the world and is amenable to laboratory experimentation at each stage of the parasite's life cycle. Here, we take stock of 5 years of experimental laboratory research carried out using Plasmodium relictum SGS1, the most prevalent avian malaria lineage in Europe, and its natural vector, the mosquito Culex pipiens. For this purpose, we compile and analyse data obtained in our laboratory in 14 different experiments. We provide statistical relationships between different infection-related parameters, including parasitaemia, gametocytaemia, host morbidity (anaemia) and transmission rates to mosquitoes. This analysis provides a wide-ranging picture of the within-host and between-host parameters that may bear on malaria transmission and epidemiology.
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Affiliation(s)
- Romain Pigeault
- MIVEGEC (UMR CNRS 5290), Montpellier, France CEFE (UMR CNRS 5175), Montpellier, France
| | | | | | - Flore Zélé
- Centre for Environmental Biology, University of Lisbon, Lisbon, Portugal
| | - Antoine Nicot
- MIVEGEC (UMR CNRS 5290), Montpellier, France CEFE (UMR CNRS 5175), Montpellier, France
| | | | | | - Ana Rivero
- MIVEGEC (UMR CNRS 5290), Montpellier, France
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56
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Josling GA, Llinás M. Sexual development in Plasmodium parasites: knowing when it's time to commit. Nat Rev Microbiol 2015; 13:573-87. [DOI: 10.1038/nrmicro3519] [Citation(s) in RCA: 138] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
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57
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An assay to probe Plasmodium falciparum growth, transmission stage formation and early gametocyte development. Nat Protoc 2015; 10:1131-42. [PMID: 26134953 DOI: 10.1038/nprot.2015.072] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Conversion from asexual proliferation to sexual differentiation initiates the production of the gametocyte, which is the malaria parasite stage required for human-to-mosquito transmission. This protocol describes an assay designed to probe the effect of drugs or other perturbations on asexual replication, sexual conversion and early gametocyte development in the major human malaria parasite Plasmodium falciparum. Synchronized asexually replicating parasites are induced for gametocyte production by the addition of conditioned medium, and they are then exposed to the treatment of interest during sexual commitment or at any subsequent stage of early gametocyte development. Flow cytometry is used to measure asexual proliferation and gametocyte production via DNA dye staining and the gametocyte-specific expression of a fluorescent protein, respectively. This screening approach may be used to identify and evaluate potential transmission-blocking compounds and to further investigate the mechanism of sexual conversion in malaria parasites. The full protocol can be completed in 11 d.
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58
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Dantzler KW, Ravel DB, Brancucci NM, Marti M. Ensuring transmission through dynamic host environments: host-pathogen interactions in Plasmodium sexual development. Curr Opin Microbiol 2015; 26:17-23. [PMID: 25867628 DOI: 10.1016/j.mib.2015.03.005] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2015] [Accepted: 03/09/2015] [Indexed: 01/08/2023]
Abstract
A renewed global commitment to malaria elimination lends urgency to understanding the biology of Plasmodium transmission stages. Recent progress toward uncovering the mechanisms underlying Plasmodium falciparum sexual differentiation and maturation reveals potential targets for transmission-blocking drugs and vaccines. The identification of parasite factors that alter sexual differentiation, including extracellular vesicles and a master transcriptional regulator, suggest that parasites make epigenetically controlled developmental decisions based on environmental cues. New insights into sexual development, especially host cell remodeling and sequestration in the bone marrow, highlight open questions regarding parasite homing to the tissue, transmigration across the vascular endothelium, and maturation in the parenchyma. Novel molecular and translational tools will provide further opportunities to define host-parasite interactions and design effective transmission-blocking therapeutics.
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Affiliation(s)
- Kathleen W Dantzler
- Department of Immunology and Infectious Diseases, Harvard T.H. Chan School of Public Health, Boston, MA 02115, USA
| | - Deepali B Ravel
- Department of Immunology and Infectious Diseases, Harvard T.H. Chan School of Public Health, Boston, MA 02115, USA
| | - Nicolas Mb Brancucci
- Department of Immunology and Infectious Diseases, Harvard T.H. Chan School of Public Health, Boston, MA 02115, USA
| | - Matthias Marti
- Department of Immunology and Infectious Diseases, Harvard T.H. Chan School of Public Health, Boston, MA 02115, USA.
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59
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Shanks GD. Hypothesis: dynamics of classical malaria epidemics show Plasmodium falciparum's survival strategy. Am J Trop Med Hyg 2015; 92:561-4. [PMID: 25624407 PMCID: PMC4350549 DOI: 10.4269/ajtmh.14-0541] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2014] [Accepted: 12/07/2014] [Indexed: 11/07/2022] Open
Abstract
Areas of marginal transmission can generate enormous lethal falciparum malaria epidemics when factors favoring the parasite shift only slightly. Although usually described in terms of vectorial capacity, medical scientists working in India in the early 20th century came to the conclusion that "an epidemic of relapses" was the key triggering event of malaria epidemics. This explanation has been largely discarded, because the biology of Plasmodium falciparum recrudescence has since been differentiated from P. vivax relapse. Using data from the Punjab in 1908 and Ceylon in 1934-1935, the genesis of malaria epidemics has been re-examined to inform current control efforts. The epidemics were focused geographically depending on recent rainfall or drought. Epidemics arose very suddenly and simultaneously in several places. Malaria spleen surveys indicated very little recent malaria transmission, and blood smears showed very few gametocytes just before the epidemic. Population stress as indicated by high grain prices because of a poor harvest caused by drought the previous year was a risk factor for malaria epidemics. Although increased female Anopheline survival because of increased humidity played an important part in the magnification of the epidemic, it does not explain its genesis. Human population stress triggering a shift toward gametocytogenesis is hypothesized as the key initiation factor for malaria epidemics. Its evolutionary significance may be that it allows the parasite to match the tropical agricultural cycle.
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Affiliation(s)
- G Dennis Shanks
- Australian Army Malaria Institute, Enoggera, Australia; School of Population Health, University of Queensland, Brisbane, Australia; Department of Zoology, University of Oxford, Oxford, United Kingdom
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60
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Sinden RE. The cell biology of malaria infection of mosquito: advances and opportunities. Cell Microbiol 2015; 17:451-66. [PMID: 25557077 PMCID: PMC4409862 DOI: 10.1111/cmi.12413] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2014] [Revised: 12/12/2014] [Accepted: 12/24/2014] [Indexed: 01/01/2023]
Abstract
Recent reviews (Feachem et al.; Alonso et al.) have concluded that in order to have a sustainable impact on the global burden of malaria, it is essential that we knowingly reduce the global incidence of infected persons. To achieve this we must reduce the basic reproductive rate of the parasites to < 1 in diverse epidemiological settings. This can be achieved by impacting combinations of the following parameters: the number of mosquitoes relative to the number of persons, the mosquito/human biting rate, the proportion of mosquitoes carrying infectious sporozoites, the daily survival rate of the infectious mosquito and the ability of malaria-infected persons to infect mosquito vectors. This paper focuses on our understanding of parasite biology underpinning the last of these terms: infection of the mosquito. The article attempts to highlight central issues that require further study to assist in the discovery of useful transmission-blocking measures.
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Affiliation(s)
- R E Sinden
- Department of Life Sciences, Imperial College London and the Jenner Institute, The University of Oxford, Oxford, UK
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61
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Malaria parasites prepare for flight. Trends Parasitol 2014; 30:551-3. [DOI: 10.1016/j.pt.2014.10.004] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2014] [Accepted: 10/17/2014] [Indexed: 01/22/2023]
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Affiliation(s)
- Sascha Brunke
- Department of Microbial Pathogenicity Mechanisms, Leibniz Institute for Natural Product Research and Infection Biology, Hans Knöll Institute (HKI), Jena, Germany
- Center for Sepsis Control and Care, Jena University Hospital, Jena, Germany
| | - Bernhard Hube
- Department of Microbial Pathogenicity Mechanisms, Leibniz Institute for Natural Product Research and Infection Biology, Hans Knöll Institute (HKI), Jena, Germany
- Center for Sepsis Control and Care, Jena University Hospital, Jena, Germany
- Friedrich Schiller University, Jena, Germany
- * E-mail:
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63
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Cornet S, Nicot A, Rivero A, Gandon S. Evolution of Plastic Transmission Strategies in Avian Malaria. PLoS Pathog 2014; 10:e1004308. [PMID: 25210974 PMCID: PMC4161439 DOI: 10.1371/journal.ppat.1004308] [Citation(s) in RCA: 75] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2014] [Accepted: 07/02/2014] [Indexed: 01/26/2023] Open
Abstract
Malaria parasites have been shown to adjust their life history traits to changing environmental conditions. Parasite relapses and recrudescences—marked increases in blood parasite numbers following a period when the parasite was either absent or present at very low levels in the blood, respectively—are expected to be part of such adaptive plastic strategies. Here, we first present a theoretical model that analyses the evolution of transmission strategies in fluctuating seasonal environments and we show that relapses may be adaptive if they are concomitant with the presence of mosquitoes in the vicinity of the host. We then experimentally test the hypothesis that Plasmodium parasites can respond to the presence of vectors. For this purpose, we repeatedly exposed birds infected by the avian malaria parasite Plasmodium relictum to the bites of uninfected females of its natural vector, the mosquito Culex pipiens, at three different stages of the infection: acute (∼34 days post infection), early chronic (∼122 dpi) and late chronic (∼291 dpi). We show that: (i) mosquito-exposed birds have significantly higher blood parasitaemia than control unexposed birds during the chronic stages of the infection and that (ii) this translates into significantly higher infection prevalence in the mosquito. Our results demonstrate the ability of Plasmodium relictum to maximize their transmission by adopting plastic life history strategies in response to the availability of insect vectors. Seasonal fluctuations in the environment affect dramatically the abundance of insect species. These fluctuations have important consequences for the transmission of vector-borne diseases. Here we contend that malaria parasites may have evolved plastic transmission strategies as an adaptation to the fluctuations in mosquito densities. First, our theoretical analysis identifies the conditions for the evolution of such plastic transmission strategies. Second, we show that in avian malaria Plasmodium parasites have the ability to increase transmission after being bitten by uninfected Culex mosquitoes. This demonstrates the ability of Plasmodium parasites to adopt plastic transmission strategies and challenges our understanding of malaria epidemiology.
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Affiliation(s)
- Stéphane Cornet
- Centre d'Ecologie Fonctionnelle et Evolutive (CEFE), UMR CNRS 5175 - Université de Montpellier - Université Paul-Valéry Montpellier - EPHE, Montpellier, France
- Maladies Infectieuses et Vecteurs: Ecologie, Génétique, Evolution et Contrôle (MIVEGEC), UMR CNRS 5290-IRD 224-UM1-UM2, Montpellier, France
| | - Antoine Nicot
- Centre d'Ecologie Fonctionnelle et Evolutive (CEFE), UMR CNRS 5175 - Université de Montpellier - Université Paul-Valéry Montpellier - EPHE, Montpellier, France
- Maladies Infectieuses et Vecteurs: Ecologie, Génétique, Evolution et Contrôle (MIVEGEC), UMR CNRS 5290-IRD 224-UM1-UM2, Montpellier, France
| | - Ana Rivero
- Maladies Infectieuses et Vecteurs: Ecologie, Génétique, Evolution et Contrôle (MIVEGEC), UMR CNRS 5290-IRD 224-UM1-UM2, Montpellier, France
| | - Sylvain Gandon
- Centre d'Ecologie Fonctionnelle et Evolutive (CEFE), UMR CNRS 5175 - Université de Montpellier - Université Paul-Valéry Montpellier - EPHE, Montpellier, France
- * E-mail:
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64
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Leggett HC, Brown SP, Reece SE. War and peace: social interactions in infections. Philos Trans R Soc Lond B Biol Sci 2014; 369:20130365. [PMID: 24686936 PMCID: PMC3982666 DOI: 10.1098/rstb.2013.0365] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
One of the most striking facts about parasites and microbial pathogens that has emerged in the fields of social evolution and disease ecology in the past few decades is that these simple organisms have complex social lives, indulging in a variety of cooperative, communicative and coordinated behaviours. These organisms have provided elegant experimental tests of the importance of relatedness, kin discrimination, cooperation and competition, in driving the evolution of social strategies. Here, we briefly review the social behaviours of parasites and microbial pathogens, including their contributions to virulence, and outline how inclusive fitness theory has helped to explain their evolution. We then take a mechanistically inspired ‘bottom-up’ approach, discussing how key aspects of the ways in which parasites and pathogens exploit hosts, namely public goods, mobile elements, phenotypic plasticity, spatial structure and multi-species interactions, contribute to the emergent properties of virulence and transmission. We argue that unravelling the complexities of within-host ecology is interesting in its own right, and also needs to be better incorporated into theoretical evolution studies if social behaviours are to be understood and used to control the spread and severity of infectious diseases.
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Affiliation(s)
- Helen C Leggett
- Department of Zoology, Oxford University, , South Parks Road, Oxford OX1 3PS, UK
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65
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Carter LM, Schneider P, Reece SE. Information use and plasticity in the reproductive decisions of malaria parasites. Malar J 2014; 13:115. [PMID: 24670151 PMCID: PMC3986881 DOI: 10.1186/1475-2875-13-115] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2013] [Accepted: 03/23/2014] [Indexed: 01/13/2023] Open
Abstract
BACKGROUND Investment in the production of transmissible stages (gametocytes) and their sex ratio are malaria parasite traits that underpin mosquito infectivity and are therefore central to epidemiology. Malaria parasites adjust their levels of investment into gametocytes and sex ratio in response to changes in the in-host environment (including red blood cell resource availability, host immune responses, competition from con-specific genotypes in mixed infections, and drug treatment). This plasticity appears to be adaptive (strategic) because parasites prioritize investment (in sexual versus asexual stages and male versus female stages) in manners predicted to maximize fitness. However, the information, or 'cues' that parasites use to detect environmental changes and make appropriate decisions about investment into gametocytes and their sex ratio are unknown. METHODS Single genotype Plasmodium chabaudi infections were exposed to 'cue' treatments consisting of intact or lysed uninfected red blood cells, lysed parasitized RBCs of the same clone or an unrelated clone, and an unmanipulated control. Infection dynamics (proportion of reticulocytes, red blood cell and asexual stage parasite densities) were monitored, and changes in gametocyte investment and sex ratio in response to cue treatments, applied either pre- or post-peak of infection were examined. RESULTS AND CONCLUSIONS A significant reduction in gametocyte density was observed in response to the presence of lysed parasite material and a borderline significant increase in sex ratio (proportion of male gametocytes) upon exposure to lysed red blood cells (both uninfected and infected) was observed. Furthermore, the changes in gametocyte density and sex ratio in response to these cues depend on the age of infection. Demonstrating that variation in gametocyte investment and sex ratio observed during infections are a result of parasite strategies (rather than the footprint of host physiology), provides a foundation to investigate the fitness consequences of plasticity and explore whether drugs could be developed to trick parasites into making suboptimal decisions.
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Affiliation(s)
- Lucy M Carter
- Institute of Evolutionary Biology, School of Biological Sciences, Ashworth Laboratories, University of Edinburgh, Edinburgh, UK
| | - Petra Schneider
- Institute of Evolutionary Biology, School of Biological Sciences, Ashworth Laboratories, University of Edinburgh, Edinburgh, UK
| | - Sarah E Reece
- Institute of Evolutionary Biology, School of Biological Sciences, Ashworth Laboratories, University of Edinburgh, Edinburgh, UK
- Centre for Immunity, Infection & Evolution, Institutes of Evolution, Immunology and Infection Research, School of Biological Sciences, Ashworth Laboratories, University of Edinburgh, Edinburgh, UK
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