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Lu HZ, Sui Y, Lobo NF, Fouque F, Gao C, Lu S, Lv S, Deng SQ, Wang DQ. Challenge and opportunity for vector control strategies on key mosquito-borne diseases during the COVID-19 pandemic. Front Public Health 2023; 11:1207293. [PMID: 37554733 PMCID: PMC10405932 DOI: 10.3389/fpubh.2023.1207293] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2023] [Accepted: 06/29/2023] [Indexed: 08/10/2023] Open
Abstract
Mosquito-borne diseases are major global health problems that threaten nearly half of the world's population. Conflicting resources and infrastructure required by the coronavirus disease 2019 (COVID-19) global pandemic have resulted in the vector control process being more demanding than ever. Although novel vector control paradigms may have been more applicable and efficacious in these challenging settings, there were virtually no reports of novel strategies being developed or implemented during COVID-19 pandemic. Evidence shows that the COVID-19 pandemic has dramatically impacted the implementation of conventional mosquito vector measures. Varying degrees of disruptions in malaria control and insecticide-treated nets (ITNs) and indoor residual spray (IRS) distributions worldwide from 2020 to 2021 were reported. Control measures such as mosquito net distribution and community education were significantly reduced in sub-Saharan countries. The COVID-19 pandemic has provided an opportunity for innovative vector control technologies currently being developed. Releasing sterile or lethal gene-carrying male mosquitoes and novel biopesticides may have advantages that are not matched by traditional vector measures in the current context. Here, we review the effects of COVID-19 pandemic on current vector control measures from 2020 to 2021 and discuss the future direction of vector control, taking into account probable evolving conditions of the COVID-19 pandemic.
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Affiliation(s)
- Hong-Zheng Lu
- Chinese Center for Disease Control and Prevention, National Institute of Parasitic Diseases, Shanghai, China
- Department of Pathogen Biology, the Key Laboratory of Microbiology and Parasitology of Anhui Province, the Key Laboratory of Zoonoses of High Institutions in Anhui, School of Basic Medical Sciences, Anhui Medical University, Hefei, China
- Department of Epidemiology and Biostatistics, School of Public Health, Anhui Medical University, Hefei, Anhui, China
| | - Yuan Sui
- Brown School, Washington University, St. Louis, MO, United States
| | - Neil F. Lobo
- Malaria Elimination Initiative, Institute for Global Health Sciences, University of California, San Francisco, San Francisco, CA, United States
- Eck Institute for Global Health, University of Notre Dame, Notre Dame, IN, United States
| | - Florence Fouque
- Research for Implementation Unit, The Special Programme for Research and Training in Tropical Diseases, World Health Organization, Geneva, Switzerland
| | - Chen Gao
- Chinese Center for Disease Control and Prevention, National Institute of Parasitic Diseases, Shanghai, China
- Department of Epidemiology and Biostatistics, School of Public Health, Anhui Medical University, Hefei, Anhui, China
| | - Shenning Lu
- Chinese Center for Disease Control and Prevention, National Institute of Parasitic Diseases, Shanghai, China
- Chinese Center for Tropical Diseases Research, Shanghai, China
- WHO Collaborating Centre for Tropical Diseases, Shanghai, China
- National Center for International Research on Tropical Diseases, Ministry of Science and Technology, Shanghai, China
- Key Laboratory of Parasite and Vector Biology, Ministry of Health, Shanghai, China
| | - Shan Lv
- Chinese Center for Disease Control and Prevention, National Institute of Parasitic Diseases, Shanghai, China
- Chinese Center for Tropical Diseases Research, Shanghai, China
- WHO Collaborating Centre for Tropical Diseases, Shanghai, China
- National Center for International Research on Tropical Diseases, Ministry of Science and Technology, Shanghai, China
- Key Laboratory of Parasite and Vector Biology, Ministry of Health, Shanghai, China
- School of Global Health, Chinese Center for Tropical Diseases Research, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | - Sheng-Qun Deng
- Department of Pathogen Biology, the Key Laboratory of Microbiology and Parasitology of Anhui Province, the Key Laboratory of Zoonoses of High Institutions in Anhui, School of Basic Medical Sciences, Anhui Medical University, Hefei, China
| | - Duo-Quan Wang
- Chinese Center for Disease Control and Prevention, National Institute of Parasitic Diseases, Shanghai, China
- Chinese Center for Tropical Diseases Research, Shanghai, China
- WHO Collaborating Centre for Tropical Diseases, Shanghai, China
- National Center for International Research on Tropical Diseases, Ministry of Science and Technology, Shanghai, China
- Key Laboratory of Parasite and Vector Biology, Ministry of Health, Shanghai, China
- School of Global Health, Chinese Center for Tropical Diseases Research, Shanghai Jiao Tong University School of Medicine, Shanghai, China
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Accoti A, Engdahl CS, Dimopoulos G. Discovery of Novel Entomopathogenic Fungi for Mosquito-Borne Disease Control. FRONTIERS IN FUNGAL BIOLOGY 2021; 2:637234. [PMID: 37744144 PMCID: PMC10512396 DOI: 10.3389/ffunb.2021.637234] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/03/2020] [Accepted: 06/28/2021] [Indexed: 09/26/2023]
Abstract
The increased application of chemical control programs has led to the emergence and spread of insecticide resistance in mosquitoes. Novel environmentally safe control strategies are currently needed for the control of disease vectors. The use of entomopathogenic fungi could be a suitable alternative to chemical insecticides. Currently, Beauveria spp. and Metarhizium spp. are the most widely used entomopathogenic fungi for mosquito control, but increasing the arsenal with additional fungi is necessary to mitigate the emergence of resistance. Entomopathogenic fungi are distributed in a wide range of habitats. We have performed a comprehensive screen for candidate mosquitocidal fungi from diverse outdoor environments in Maryland and Puerto Rico. An initial screening of 22 fungi involving exposure of adult Anopheles gambiae to 2-weeks-old fungal cultures identified five potent pathogenic fungi, one of which is unidentified and the remaining four belonging to the three genera Galactomyces sp., Isaria sp. and Mucor sp. These fungi were then screened against Aedes aegypti, revealing Isaria sp. as a potent mosquito killer. The entomopathogenic effects were confirmed through spore-dipping assays. We also probed further into the killing mechanisms of these fungi and investigated whether the mosquitocidal activities were the result of potential toxic fungus-produced metabolites. Preliminary assays involving the exposure of mosquitoes to sterile filtered fungal liquid cultures showed that Galactomyces sp., Isaria sp. and the unidentified isolate 1 were the strongest producers of factors showing lethality against An. gambiae. We have identified five fungi that was pathogenic for An. gambiae and one for Ae. aegypti, among these fungi, four of them (two strains of Galactomyces sp., Mucor sp., and the unidentified isolate 1) have never previously been described as lethal to insects. Further characterization of these entomopathogenic fungi and their metabolites needs to be done to confirm their potential use in biologic control against mosquitoes.
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Affiliation(s)
| | | | - George Dimopoulos
- W. Harry Feinstone Department of Molecular Microbiology and Immunology, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, MD, United States
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Hargrove JW. A model for the relationship between wing fray and chronological and ovarian ages in tsetse (Glossina spp). MEDICAL AND VETERINARY ENTOMOLOGY 2020; 34:251-263. [PMID: 32222085 DOI: 10.1111/mve.12439] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/12/2019] [Revised: 02/18/2020] [Accepted: 03/05/2020] [Indexed: 06/10/2023]
Abstract
Age-dependent mortality changes in haematophagous insects are difficult to measure but are important determinants of population dynamics and vectorial capacity. A Markov process was used to model age-dependent changes in wing fray in tsetse (Glossina spp), calibrated using published mark-recapture data for male G. m. morsitans in Tanzania. The model was applied to female G. m. morsitans, captured in Zimbabwe using a vehicle-mounted electric net and subjected to ovarian dissection and wing fray analysis. Rates of fray increased significantly with age in males but not females, where the rate was constant for ovarian categories 0-3. A jump in mean fray between ovarian categories 3 and 4 + 4n is consistent with the latter category including flies that have ovulated 4, 8, 12, 16 times and so on. The magnitude of the jump could, theoretically, facilitate improved mortality estimates. In practice, although knowledge of fly mortality was required for modelling wing fray, mortality estimates derived from ovarian dissection data are independent of patterns and rates of change in wing fray. Significantly better fits to ovarian age data resulted when age-specific mortality was modelled as the sum of two exponentials, with high mortality in young and old flies, than when mortality was constant at 2.3% per day.
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Affiliation(s)
- J W Hargrove
- SACEMA, University of Stellenbosch, Stellenbosch, South Africa
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Abstract
Driving endonuclease genes (DEGs) spread through a population by a non-Mendelian mechanism. In a heterozygote, the protein encoded by a DEG causes a double-strand break in the homologous chromosome opposite to where its gene is inserted and when the break is repaired using the homologue as a template the DEG heterozygote is converted to a homozygote. Some DEGs occur naturally while several classes of endonucleases can be engineered to spread in this way, with CRISPR-Cas9 based systems being particularly flexible. There is great interest in using driving endonuclease genes to impose a genetic load on insects that vector diseases or are economic pests to reduce their population density, or to introduce a beneficial gene such as one that might interrupt disease transmission. This paper reviews both the population genetics and population dynamics of DEGs. It summarises the theory that guides the design of DEG constructs intended to perform different functions. It also reviews the studies that have explored the likelihood of resistance to DEG phenotypes arising, and how this risk may be reduced. The review is intended for a general audience and mathematical details are kept to a minimum.
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Affiliation(s)
- H Charles J Godfray
- Department of Zoology, University of Oxford, South Parks Road, Oxford, OX1 3PS, UK.
| | - Ace North
- Department of Zoology, University of Oxford, South Parks Road, Oxford, OX1 3PS, UK
| | - Austin Burt
- Department of Life Sciences, Imperial College London, Silwood Park, Ascot, Berkshire, SL5 7PY, UK
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Smith TA, Chitnis N, Penny M, Tanner M. Malaria Modeling in the Era of Eradication. Cold Spring Harb Perspect Med 2017; 7:cshperspect.a025460. [PMID: 28003280 DOI: 10.1101/cshperspect.a025460] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Mathematical models provide the essential basis of rational research and development strategies in malaria, informing the choice of which technologies to target, which deployment strategies to consider, and which populations to focus on. The Internet and remote sensing technologies also enable assembly of ever more relevant field data. Together with supercomputing technology, this has made available timely descriptions of the geography of malaria transmission and disease across the world and made it possible for policy and planning to be informed by detailed simulations of the potential impact of intervention programs. These information technology advances do not replace the basic understanding of the dynamics of malaria transmission that should be embedded in the thinking of anyone planning malaria interventions. The appropriate use of modeling may determine whether we are living in an era of hubris or indeed in an age of eradication.
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Affiliation(s)
- Thomas A Smith
- Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, Basel CH 4002, Switzerland; and University of Basel, Basel CH 4001, Switzerland
| | - Nakul Chitnis
- Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, Basel CH 4002, Switzerland; and University of Basel, Basel CH 4001, Switzerland
| | - Melissa Penny
- Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, Basel CH 4002, Switzerland; and University of Basel, Basel CH 4001, Switzerland
| | - Marcel Tanner
- Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, Basel CH 4002, Switzerland; and University of Basel, Basel CH 4001, Switzerland
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6
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Evaluating the usefulness of paratransgenesis for malaria control. Math Biosci 2016; 277:117-25. [PMID: 27140529 DOI: 10.1016/j.mbs.2016.04.005] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2015] [Revised: 04/11/2016] [Accepted: 04/24/2016] [Indexed: 11/23/2022]
Abstract
Malaria is a serious global health problem which is especially devastating to the developing world. Most malaria control programs use insecticides for controlling mosquito populations. Large scale usage of these insecticides exerts massive selection pressure on mosquitoes resulting in insecticide resistant mosquito breeds. Thus, developing alternative strategies are crucial for sustainable malaria control. Here, we explore the usefulness of an alternative strategy, paratransgenesis: the introduction of genetically engineered plasmodium killing bacteria inside the mosquito gut. The genetically modified bacterial culture is housed in cotton balls dipped in a sugar solution (sugar bait) and they enter a mosquito's midgut when it drinks from a sugar bait. We study scenarios where vectors and hosts mix homogeneously as well as heterogeneously and calculate the amount of baits required to prevent a malaria outbreak. Given the baits are attractive, we show that the basic reproductive number drops rapidly with the increase in bait density. Furthermore, we propose a targeted bait distribution strategy for minimizing the reproductive number for the heterogeneous case. Our results can prove to be useful for designing future experiments and field trials of alternative malaria control mechanisms and they also have implications on the development of malaria control programs.
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González-Parra G, Chen-Charpentier BM, Bermúdez M. Modeling Chagas Disease at Population Level to Explain Venezuela's Real Data. Osong Public Health Res Perspect 2016; 6:288-301. [PMID: 26929912 PMCID: PMC4677493 DOI: 10.1016/j.phrp.2015.09.001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2015] [Revised: 08/08/2015] [Accepted: 09/25/2015] [Indexed: 12/19/2022] Open
Abstract
Objectives In this paper we present an age-structured epidemiological model for Chagas disease. This model includes the interactions between human and vector populations that transmit Chagas disease. Methods The human population is divided into age groups since the proportion of infected individuals in this population changes with age as shown by real prevalence data. Moreover, the age-structured model allows more accurate information regarding the prevalence, which can help to design more specific control programs. We apply this proposed model to data from the country of Venezuela for two periods, 1961–1971, and 1961–1991 taking into account real demographic data for these periods. Results Numerical computer simulations are presented to show the suitability of the age-structured model to explain the real data regarding prevalence of Chagas disease in each of the age groups. In addition, a numerical simulation varying the death rate of the vector is done to illustrate prevention and control strategies against Chagas disease. Conclusion The proposed model can be used to determine the effect of control strategies in different age groups.
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Affiliation(s)
- Gilberto González-Parra
- Grupo Matemática Multidisciplinar, Faculdad Ingeniería Universidad de los Andes, Venezuela; Centro de Investigaciones en Matemática Aplicada (CIMA), Universidad de los Andes, Venezuela; Department of Mathematics, University of Texas at Arlington, Arlington, TX, USA
| | | | - Moises Bermúdez
- Grupo Matemática Multidisciplinar, Faculdad Ingeniería Universidad de los Andes, Venezuela; Universidad Nacional Experimental Sur de Lago Jesús María Semprum, Venezuela
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Chamchod F, Cosner C, Cantrell RS, Beier JC, Ruan S. Transmission Dynamics of Rift Valley Fever Virus: Effects of Live and Killed Vaccines on Epizootic Outbreaks and Enzootic Maintenance. Front Microbiol 2016; 6:1568. [PMID: 26869999 PMCID: PMC4740790 DOI: 10.3389/fmicb.2015.01568] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2015] [Accepted: 12/27/2015] [Indexed: 01/14/2023] Open
Abstract
Rift Valley fever virus (RVFV) is an arthropod-borne viral pathogen that causes significant morbidity and mortality in small ruminants throughout Africa and the Middle East. Due to the sporadic and explosive nature of RVF outbreaks, vaccination has proved challenging to reduce RVFV infection in the ruminant population. Currently, there are two available types of vaccines, live and killed, in endemic areas. In this study, two mathematical models have been developed to explore the impact of live and killed vaccines on the transmission dynamics of RVFV. We demonstrate in general that vaccination helps reduce the severity of RVF outbreaks and that less delay in implementation and more vaccination attempts and effective vaccines can reduce the outbreak magnitude and the endemic number of RVFV. However, an introduction of a number of ruminants vaccinated by live vaccines in RVFV-free areas may cause an outbreak and RVFV may become endemic if there is sustained use of live vaccines. Other factors that are the important determinants of RVF outbreaks include: unsustained vaccination programs, recruitment of susceptible ruminants, and the seasonal abundance of mosquitoes.
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Affiliation(s)
- Farida Chamchod
- Department of Mathematics, Faculty of Science, Mahidol University Bangkok, Thailand
| | - Chris Cosner
- Department of Mathematics, University of Miami Coral Gables, FL, USA
| | | | - John C Beier
- Department of Public Health Sciences, Miller School of Medicine, University of Miami Miami, FL, USA
| | - Shigui Ruan
- Department of Mathematics, University of Miami Coral Gables, FL, USA
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Heinig RL, Paaijmans KP, Hancock PA, Thomas MB. The potential for fungal biopesticides to reduce malaria transmission under diverse environmental conditions. J Appl Ecol 2015; 52:1558-1566. [PMID: 26792946 PMCID: PMC4716011 DOI: 10.1111/1365-2664.12522] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The effectiveness of conventional malaria vector control is being threatened by the spread of insecticide resistance. One promising alternative to chemicals is the use of naturally-occurring insect-killing fungi. Numerous laboratory studies have shown that isolates of fungal pathogens such as Beauveria bassiana can infect and kill adult mosquitoes, including those resistant to chemical insecticides.Unlike chemical insecticides, fungi may take up to a week or more to kill mosquitoes following exposure. This slow kill speed can still reduce malaria transmission because the malaria parasite itself takes at least eight days to complete its development within the mosquito. However, both fungal virulence and parasite development rate are strongly temperature-dependent, so it is possible that biopesticide efficacy could vary across different transmission environments.We examined the virulence of a candidate fungal isolate against two key malaria vectors at temperatures from 10-34 °C. Regardless of temperature, the fungus killed more than 90% of exposed mosquitoes within the predicted duration of the malarial extrinsic incubation period, a result that was robust to realistic diurnal temperature variation.We then incorporated temperature sensitivities of a suite of mosquito, parasite and fungus life-history traits that are important determinants of malaria transmission into a stage-structured malaria transmission model. The model predicted that, at achievable daily fungal infection rates, fungal biopesticides have the potential to deliver substantial reductions in the density of malaria-infectious mosquitoes across all temperatures representative of malaria transmission environments.Synthesis and applications. Our study combines empirical data and theoretical modelling to prospectively evaluate the potential of fungal biopesticides to control adult malaria vectors. Our results suggest that Beauveria bassiana could be a potent tool for malaria control and support further development of fungal biopesticides to manage infectious disease vectors.
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Affiliation(s)
- R L Heinig
- Center for Infectious Disease Dynamics and Department of Entomology, The Pennsylvania State University, University Park, PA, USA
| | - Krijn P Paaijmans
- ISGlobal, Barcelona Centre for International Health Research (CRESIB), Hospital Clínic-Universitat de Barcelona, Barcelona, Spain
| | | | - Matthew B Thomas
- Center for Infectious Disease Dynamics and Department of Entomology, The Pennsylvania State University, University Park, PA, USA
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10
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The potential for fungal biopesticides to reduce malaria transmission under diverse environmental conditions. Curr Nutr Rep 2015. [PMID: 26792946 DOI: 10.1007/s13668-012-0032-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The effectiveness of conventional malaria vector control is being threatened by the spread of insecticide resistance. One promising alternative to chemicals is the use of naturally-occurring insect-killing fungi. Numerous laboratory studies have shown that isolates of fungal pathogens such as Beauveria bassiana can infect and kill adult mosquitoes, including those resistant to chemical insecticides.Unlike chemical insecticides, fungi may take up to a week or more to kill mosquitoes following exposure. This slow kill speed can still reduce malaria transmission because the malaria parasite itself takes at least eight days to complete its development within the mosquito. However, both fungal virulence and parasite development rate are strongly temperature-dependent, so it is possible that biopesticide efficacy could vary across different transmission environments.We examined the virulence of a candidate fungal isolate against two key malaria vectors at temperatures from 10-34 °C. Regardless of temperature, the fungus killed more than 90% of exposed mosquitoes within the predicted duration of the malarial extrinsic incubation period, a result that was robust to realistic diurnal temperature variation.We then incorporated temperature sensitivities of a suite of mosquito, parasite and fungus life-history traits that are important determinants of malaria transmission into a stage-structured malaria transmission model. The model predicted that, at achievable daily fungal infection rates, fungal biopesticides have the potential to deliver substantial reductions in the density of malaria-infectious mosquitoes across all temperatures representative of malaria transmission environments.Synthesis and applications. Our study combines empirical data and theoretical modelling to prospectively evaluate the potential of fungal biopesticides to control adult malaria vectors. Our results suggest that Beauveria bassiana could be a potent tool for malaria control and support further development of fungal biopesticides to manage infectious disease vectors.
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11
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Modelling Anopheles gambiae s.s. Population Dynamics with Temperature- and Age-Dependent Survival. INTERNATIONAL JOURNAL OF ENVIRONMENTAL RESEARCH AND PUBLIC HEALTH 2015; 12:5975-6005. [PMID: 26030468 PMCID: PMC4483682 DOI: 10.3390/ijerph120605975] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/31/2015] [Revised: 05/21/2015] [Accepted: 05/21/2015] [Indexed: 11/17/2022]
Abstract
Climate change and global warming are emerging as important threats to human health, particularly through the potential increase in vector- and water-borne diseases. Environmental variables are known to affect substantially the population dynamics and abundance of the poikilothermic vectors of disease, but the exact extent of this sensitivity is not well established. Focusing on malaria and its main vector in Africa, Anopheles gambiae sensu stricto, we present a set of novel mathematical models of climate-driven mosquito population dynamics motivated by experimental data suggesting that in An. gambiae, mortality is temperature and age dependent. We compared the performance of these models to that of a "standard" model ignoring age dependence. We used a longitudinal dataset of vector abundance over 36 months in sub-Saharan Africa for comparison between models that incorporate age dependence and one that does not, and observe that age-dependent models consistently fitted the data better than the reference model. This highlights that including age dependence in the vector component of mosquito-borne disease models may be important to predict more reliably disease transmission dynamics. Further data and studies are needed to enable improved fitting, leading to more accurate and informative model predictions for the An. gambiae malaria vector as well as for other disease vectors.
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12
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Landscape Epidemiology Modeling Using an Agent-Based Model and a Geographic Information System. LAND 2015. [DOI: 10.3390/land4020378] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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Trypanosoma cruzi, etiological agent of Chagas disease, is virulent to its triatomine vector Rhodnius prolixus in a temperature-dependent manner. PLoS Negl Trop Dis 2015; 9:e0003646. [PMID: 25793495 PMCID: PMC4368190 DOI: 10.1371/journal.pntd.0003646] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2014] [Accepted: 02/25/2015] [Indexed: 12/05/2022] Open
Abstract
It is often assumed that parasites are not virulent to their vectors. Nevertheless, parasites commonly exploit their vectors (nutritionally for example) so these can be considered a form of host. Trypanosoma cruzi, a protozoan found in mammals and triatomine bugs in the Americas, is the etiological agent of Chagas disease that affects man and domestic animals. While it has long been considered avirulent to its vectors, a few reports have indicated that it can affect triatomine fecundity. We tested whether infection imposed a temperature-dependent cost on triatomine fitness. We held infected insects at four temperatures between 21 and 30°C and measured T. cruzi growth in vitro at the same temperatures in parallel. Trypanosoma cruzi infection caused a considerable delay in the time the insects took to moult (against a background effect of temperature accelerating moult irrespective of infection status). Trypanosoma cruzi also reduced the insects’ survival, but only at the intermediate temperatures of 24 and 27°C (against a background of increased mortality with increasing temperatures). Meanwhile, in vitro growth of T. cruzi increased with temperature. Our results demonstrate virulence of a protozoan agent of human disease to its insect vector under these conditions. It is of particular note that parasite-induced mortality was greatest over the range of temperatures normally preferred by these insects, probably implying adaptation of the parasite to perform well at these temperatures. Therefore we propose that triggering this delay in moulting is adaptive for the parasites, as it will delay the next bloodmeal taken by the bug, thus allowing the parasites time to develop and reach the insect rectum in order to make transmission to a new vertebrate host possible. Parasites are often assumed to cause little harm to their arthropod vectors, even though they commonly reproduce inside the arthropods and exploit their nutrients, even causing lesions when crossing internal barriers. Thus, the interests of parasite and vector may well not be aligned and we can expect the parasite to exploit its vector just as it does with its main host, with consequent negative effects on the vector’s fitness. Here, we show that this occurs with Trypanosoma cruzi in its bug vector (T. cruzi causes Chagas disease, affecting ca. 8 million people and disease management is principally attained via vector control). Our results indicate that the parasites delay insect moulting, which is likely beneficial to them as they need time to develop in the insect before the next bloodmeal (that only occurs post-moult). We also show parasite-induced mortality over the narrow range of temperatures which the insect prefers and over which it performs best. In vitro growth of the parasite increases with temperature and we discuss how this may help explain the effects in vivo. Overall, these results will be important to understand the epidemiology of Chagas disease and provide an evolutionary context to explain the parasite′s interaction with its vector.
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El-Maghraby S, Nawwar GA, Bakr RFA, Helmy N, Kamel OMHM. Toxicological studies for some agricultural waste extracts on mosquito larvae and experimental animals. Asian Pac J Trop Biomed 2015; 2:558-63. [PMID: 23569971 DOI: 10.1016/s2221-1691(12)60097-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2011] [Revised: 10/27/2011] [Accepted: 12/16/2011] [Indexed: 11/16/2022] Open
Abstract
OBJECTIVE To evaluate some agricultural waste extracts as insecticide and their effects on enzyme activities in liver and kidney of male mice. METHODS The insecticidal activity of five tested compounds (one crude extract and 4 waste compounds) was bioassay against the 3rd instars of the Culex pipiens (Cx. pipiens) larvae in the laboratory. The LC50 values of eucalyptol, apricot kernel, Rice bran, corn, black liquor and white liquor are 91.45, 1 166.1, 1 203.3, 21 449.65, 4 025.78 and 6 343.18 ppm, respectively. Selection of the compounds for the subsequent studies was not only dependent on LC50 values but also on the persistence of these wastes products on large scale. RESULTS White and black liquor did not produce any gross effect at 200 mg/Kg body weight. No apparent toxic symptoms were observed in tested animals during the whole period of the experiment which run out for 14 days. No statistically significance was observed in the enzyme cholinesterase activity, the activities of liver enzymes and kidney function in treated mice with black and white liquors. While, no and slight inhibition was observed after the 2 weeks of treatment period with deltamethrin and fenitrothion reached to about 24% in plasma cholinesterase enzyme activity. Significantly increase in the activities of liver enzymes and kidney function in treated mice with deltamethrin and fenitrothion. CONCLUSIONS Black liquor can be used efficiently to control Cx. pipiens larvae under laboratory condition. Environmental problem caused by rice straw can be solved by converting the waste material to beneficial natural selective insecticide.
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Affiliation(s)
- Somia El-Maghraby
- Applied organic chemistry Department, National Research Centre, Cairo, Egypt
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Arifin SMN, Zhou Y, Davis GJ, Gentile JE, Madey GR, Collins FH. An agent-based model of the population dynamics of Anopheles gambiae. Malar J 2014; 13:424. [PMID: 25373418 PMCID: PMC4233045 DOI: 10.1186/1475-2875-13-424] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2014] [Accepted: 10/26/2014] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND Agent-based models (ABMs) have been used to model the behaviour of individual mosquitoes and other aspects of malaria. In this paper, a conceptual entomological model of the population dynamics of Anopheles gambiae and the agent-based implementations derived from it are described. Hypothetical vector control interventions (HVCIs) are implemented to target specific activities in the mosquito life cycle, and their impacts are evaluated. METHODS The core model is described in terms of the complete An. gambiae mosquito life cycle. Primary features include the development and mortality rates in different aquatic and adult stages, the aquatic habitats and oviposition. The density- and age-dependent larval and adult mortality rates (vector senescence) allow the model to capture the age-dependent aspects of the mosquito biology. Details of hypothetical interventions are also described. RESULTS Results show that with varying coverage and temperature ranges, the hypothetical interventions targeting the gonotrophic cycle stages produce higher impacts than the rest in reducing the potentially infectious female (PIF) mosquito populations, due to their multi-hour mortality impacts and their applicability at multiple gonotrophic cycles. Thus, these stages may be the most effective points of target for newly developed and novel interventions. A combined HVCI with low coverage can produce additive synergistic impacts and can be more effective than isolated HVCIs with comparatively higher coverages. It is emphasized that although the model described in this paper is designed specifically around the mosquito An. gambiae, it could effectively apply to many other major malaria vectors in the world (including the three most efficient nominal anopheline species An. gambiae, Anopheles coluzzii and Anopheles arabiensis) by incorporating a variety of factors (seasonality cycles, rainfall, humidity, etc.). Thus, the model can essentially be treated as a generic Anopheles model, offering an excellent framework for such extensions. The utility of the core model has also been demonstrated by several other applications, each of which investigates well-defined biological research questions across a variety of dimensions (including spatial models, insecticide resistance, and sterile insect techniques).
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Affiliation(s)
- SM Niaz Arifin
- />Department of Computer Science and Engineering, University of Notre Dame, Notre Dame, IN 46556 USA
| | - Ying Zhou
- />Department of Computer Science and Engineering, University of Notre Dame, Notre Dame, IN 46556 USA
| | - Gregory J Davis
- />Department of Computer Science and Engineering, University of Notre Dame, Notre Dame, IN 46556 USA
| | - James E Gentile
- />Department of Computer Science and Engineering, University of Notre Dame, Notre Dame, IN 46556 USA
| | - Gregory R Madey
- />Department of Computer Science and Engineering, University of Notre Dame, Notre Dame, IN 46556 USA
| | - Frank H Collins
- />Department of Computer Science and Engineering, University of Notre Dame, Notre Dame, IN 46556 USA
- />Department of Biological Sciences, University of Notre Dame, 100 Galvin Life Sciences Center, Notre Dame, IN 46556 USA
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Christiansen-Jucht C, Parham PE, Saddler A, Koella JC, Basáñez MG. Temperature during larval development and adult maintenance influences the survival of Anopheles gambiae s.s. Parasit Vectors 2014; 7:489. [PMID: 25367091 PMCID: PMC4236470 DOI: 10.1186/s13071-014-0489-3] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2014] [Accepted: 10/13/2014] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Malaria transmission depends on vector life-history parameters and population dynamics, and particularly on the survival of adult Anopheles mosquitoes. These dynamics are sensitive to climatic and environmental factors, and temperature is a particularly important driver. Data currently exist on the influence of constant and fluctuating adult environmental temperature on adult Anopheles gambiae s.s. survival and on the effect of larval environmental temperature on larval survival, but none on how larval temperature affects adult life-history parameters. METHODS Mosquito larvae and pupae were reared individually at different temperatures (23 ± 1°C, 27 ± 1°C, 31 ± 1°C, and 35 ± 1°C), 75 ± 5% relative humidity. Upon emergence into imagoes, individual adult females were either left at their larval temperature or placed at a different temperature within the range above. Survival was monitored every 24 hours and data were analysed using non-parametric and parametric methods. The Gompertz distribution fitted the survivorship data better than the gamma, Weibull, and exponential distributions overall and was adopted to describe mosquito mortality rates. RESULTS Increasing environmental temperature during the larval stages decreased larval survival (p < 0.001). Increases of 4°C (from 23°C to 27°C, 27°C to 31°C, and 31°C to 35°C), 8°C (27°C to 35°C) and 12°C (23°C to 35°C) statistically significantly increased larval mortality (p < 0.001). Higher environmental temperature during the adult stages significantly lowered adult survival overall (p < 0.001), with increases of 4°C and 8°C significantly influencing survival (p < 0.001). Increasing the larval environment temperature also significantly increased adult mortality overall (p < 0.001): a 4°C increase (23°C to 27°C) did not significantly affect adult survival (p > 0.05), but an 8°C increase did (p < 0.05). The effect of a 4°C increase in larval temperature from 27°C to 31°C depended on the adult environmental temperature. The data also suggest that differences between the temperatures of the larval and adult environments affects adult mosquito survival. CONCLUSIONS Environmental temperature affects Anopheles survival directly during the juvenile and adult stages, and indirectly, since temperature during larval development significantly influences adult survival. These results will help to parameterise more reliable mathematical models investigating the potential impact of temperature and global warming on malaria transmission.
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Affiliation(s)
- Céline Christiansen-Jucht
- Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine (St Mary's campus), Imperial College London, Norfolk Place, London, W2 1PG, UK.
| | - Paul E Parham
- Department of Public Health and Policy, Faculty of Health and Life Sciences, University of Liverpool, Liverpool, L69 3GL, UK. .,Grantham Institute for Climate Change, Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, St. Mary's campus, Imperial College London, London, W2 1PG, UK.
| | - Adam Saddler
- Division of Biology, Faculty of Life Sciences, Imperial College London, Silwood Park Campus, Ascot, SL5 2PZ, Berkshire, UK.
| | - Jacob C Koella
- Division of Biology, Faculty of Life Sciences, Imperial College London, Silwood Park Campus, Ascot, SL5 2PZ, Berkshire, UK. .,Present address : Faculté des Sciences, Institut de Biologie, Université de Neuchâtel, Rue Emile-Argand 11, CH-2000, Neuchâtel, Switzerland.
| | - María-Gloria Basáñez
- Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine (St Mary's campus), Imperial College London, Norfolk Place, London, W2 1PG, UK.
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Wang S, Jacobs-Lorena M. Genetic approaches to interfere with malaria transmission by vector mosquitoes. Trends Biotechnol 2013; 31:185-93. [PMID: 23395485 PMCID: PMC3593784 DOI: 10.1016/j.tibtech.2013.01.001] [Citation(s) in RCA: 110] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2012] [Revised: 01/03/2013] [Accepted: 01/03/2013] [Indexed: 11/20/2022]
Abstract
Malaria remains one of the most devastating diseases worldwide, causing over 1 million deaths every year. The most vulnerable stages of Plasmodium development in the vector mosquito occur in the midgut lumen, making the midgut a prime target for intervention. Mosquito transgenesis and paratransgenesis are two novel strategies that aim at rendering the vector incapable of sustaining Plasmodium development. Mosquito transgenesis involves direct genetic engineering of the mosquito itself for delivery of anti-Plasmodium effector molecules. Conversely, paratransgenesis involves the genetic modification of mosquito symbionts for expression of anti-pathogen effector molecules. Here we consider both genetic manipulation strategies for rendering mosquitoes refractory to Plasmodium infection, and discuss challenges for the translation of laboratory findings to field applications.
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Affiliation(s)
- Sibao Wang
- Key Laboratory of Insect Developmental and Evolutionary Biology, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200032, China.
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Pollitt LC, Churcher TS, Dawes EJ, Khan SM, Sajid M, Basáñez MG, Colegrave N, Reece SE. Costs of crowding for the transmission of malaria parasites. Evol Appl 2013; 6:617-29. [PMID: 23789029 PMCID: PMC3684743 DOI: 10.1111/eva.12048] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2012] [Revised: 12/13/2012] [Accepted: 12/13/2012] [Indexed: 01/03/2023] Open
Abstract
The utility of using evolutionary and ecological frameworks to understand the dynamics of infectious diseases is gaining increasing recognition. However, integrating evolutionary ecology and infectious disease epidemiology is challenging because within-host dynamics can have counterintuitive consequences for between-host transmission, especially for vector-borne parasites. A major obstacle to linking within- and between-host processes is that the drivers of the relationships between the density, virulence, and fitness of parasites are poorly understood. By experimentally manipulating the intensity of rodent malaria (Plasmodium berghei) infections in Anopheles stephensi mosquitoes under different environmental conditions, we show that parasites experience substantial density-dependent fitness costs because crowding reduces both parasite proliferation and vector survival. We then use our data to predict how interactions between parasite density and vector environmental conditions shape within-vector processes and onward disease transmission. Our model predicts that density-dependent processes can have substantial and unexpected effects on the transmission potential of vector-borne disease, which should be considered in the development and evaluation of transmission-blocking interventions.
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Affiliation(s)
- Laura C Pollitt
- Institute of Evolutionary Biology, University of Edinburgh Edinburgh, UK ; Center for Infectious Disease Dynamics, Pennsylvania State University University Park, PA, USA
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Paaijmans KP, Cator LJ, Thomas MB. Temperature-dependent pre-bloodmeal period and temperature-driven asynchrony between parasite development and mosquito biting rate reduce malaria transmission intensity. PLoS One 2013; 8:e55777. [PMID: 23383280 PMCID: PMC3561307 DOI: 10.1371/journal.pone.0055777] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2012] [Accepted: 01/03/2013] [Indexed: 11/30/2022] Open
Abstract
A mosquito needs to bite at least twice for malaria transmission to occur: once to acquire parasites and, after these parasites complete their development in their mosquito host, once to transmit the parasites to the next vertebrate host. Here we investigate the relationship between temperature, parasite development, and biting frequency in a mosquito-rodent malaria model system. We show that the pre-bloodmeal period (the time lag between mosquito emergence and first bloodmeal) increases at lower temperatures. In addition, parasite development time and feeding exhibit different thermal sensitivities such that mosquitoes might not be ready to feed at the point at which the parasite is ready to be transmitted. Exploring these effects using a simple theoretical model of human malaria shows that delays in infection and transmission can reduce the vectorial capacity of malaria mosquitoes by 20 to over 60%, depending on temperature. These delays have important implications for disease epidemiology and control, and should be considered in future transmission models.
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Affiliation(s)
- Krijn P Paaijmans
- Center for Infectious Disease Dynamics and Department of Entomology, Pennsylvania State University, University Park, Pennsylvania, United States of America.
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20
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Prospective malaria control using entomopathogenic fungi: comparative evaluation of impact on transmission and selection for resistance. Malar J 2012; 11:383. [PMID: 23171286 PMCID: PMC3519523 DOI: 10.1186/1475-2875-11-383] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2012] [Accepted: 10/03/2012] [Indexed: 12/18/2022] Open
Abstract
Background Chemical insecticides against adult mosquitoes are a key element in most malaria management programmes, but their efficacy is threatened by the evolution of insecticide-resistant mosquitoes. By killing only older mosquitoes, entomopathogenic fungi can in principle significantly impact parasite transmission while imposing much less selection for resistance. Here an assessment is made as to which of the wide range of possible virulence characteristics for fungal biopesticides best realise this potential. Methods With mathematical models that capture relevant timings and survival probabilities within successive feeding cycles, transmission and resistance-management metrics are used to compare susceptible and resistant mosquitoes exposed to no intervention, to conventional instant-kill interventions, and to delayed-action biopesticides with a wide range of virulence characteristics. Results Fungal biopesticides that generate high rates of mortality at around the time mosquitoes first become able to transmit the malaria parasite offer potential for large reductions in transmission while imposing low fitness costs. The best combinations of control and resistance management are generally accessed at high levels of coverage. Strains which have high virulence in malaria-infected mosquitoes but lower virulence in malaria-free mosquitoes offer the ultimate benefit in terms of minimizing selection pressure whilst maximizing impact on transmission. Exploiting this phenotype should be a target for product development. For indoor residual spray programmes, biopesticides may offer substantial advantages over the widely used pyrethroid-based insecticides. Not only do fungal biopesticides provide substantial resistance management gains in the long term, they may also provide greater reductions in transmission before resistance has evolved. This is because fungal spores do not have contact irritancy, reducing the chances that a blood-fed mosquito can survive an encounter and thus live long enough to transmit malaria. Conclusions Delayed-action products, such as fungal biopesticides, have the potential to achieve reductions in transmission comparable with those achieved with existing instant-kill insecticides, and to sustain this control for substantially longer once resistant alleles arise. Given the current insecticide resistance crisis, efforts should continue to fully explore the operational feasibility of this alternative approach.
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Blanford S, Jenkins NE, Read AF, Thomas MB. Evaluating the lethal and pre-lethal effects of a range of fungi against adult Anopheles stephensi mosquitoes. Malar J 2012; 11:365. [PMID: 23126549 PMCID: PMC3520692 DOI: 10.1186/1475-2875-11-365] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2012] [Accepted: 10/05/2012] [Indexed: 02/07/2023] Open
Abstract
BACKGROUND Insecticide resistance is seriously undermining efforts to eliminate malaria. In response, research on alternatives to the use of chemical insecticides against adult mosquito vectors has been increasing. Fungal entomopathogens formulated as biopesticides have received much attention and have shown considerable potential. This research has necessarily focused on relatively few fungal isolates in order to 'prove concept'. Further, most attention has been paid to examining fungal virulence (lethality) and not the other properties of fungal infection that might also contribute to reducing transmission potential. Here, a range of fungal isolates were screened to examine variation in virulence and how this relates to additional pre-lethal reductions in feeding propensity. METHODS The Asian malaria vector, Anopheles stephensi was exposed to 17 different isolates of entomopathogenic fungi belonging to species of Beauveria bassiana, Metarhizium anisopliae, Metarhizium acridum and Isaria farinosus. Each isolate was applied to a test substrate at a standard dose rate of 1×109 spores ml-1 and the mosquitoes exposed for six hours. Subsequently the insects were removed to mesh cages where survival was monitored over the next 14 days. During this incubation period the mosquitoes' propensity to feed was assayed for each isolate by offering a feeding stimulant at the side of the cage and recording the number probing. RESULTS AND CONCLUSIONS Fungal isolates showed a range of virulence to A. stephensi with some causing >80% mortality within 7 days, while others caused little increase in mortality relative to controls over the study period. Similarly, some isolates had a large impact on feeding propensity, causing >50% pre-lethal reductions in feeding rate, whereas other isolates had very little impact. There was clear correlation between fungal virulence and feeding reduction with virulence explaining nearly 70% of the variation in feeding reduction. However, there were some isolates where either feeding decline was not associated with high virulence, or virulence did not automatically prompt large declines in feeding. These results are discussed in the context of choosing optimum fungal isolates for biopesticide development.
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Affiliation(s)
- Simon Blanford
- Center for Infectious Disease Dynamics, Department of Biology, Penn State University Mueller Laboratory, University Park, PA 16802, USA.
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22
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Blanford S, Jenkins NE, Christian R, Chan BHK, Nardini L, Osae M, Koekemoer L, Coetzee M, Read AF, Thomas MB. Storage and persistence of a candidate fungal biopesticide for use against adult malaria vectors. Malar J 2012; 11:354. [PMID: 23098323 PMCID: PMC3506477 DOI: 10.1186/1475-2875-11-354] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2012] [Accepted: 10/18/2012] [Indexed: 11/12/2022] Open
Abstract
Background New products aimed at augmenting or replacing chemical insecticides must have operational profiles that include both high efficacy in reducing vector numbers and/or blocking parasite transmission and be long lasting following application. Research aimed at developing fungal spores as a biopesticide for vector control have shown considerable potential yet have not been directly assessed for their viability after long-term storage or following application in the field. Methods Spores from a single production run of the entomopathogenic fungi Beauveria bassiana were dried and then stored under refrigeration at 7°C. After 585 days these spores were sub-sampled and placed at either 22°C, 26°C or 32°C still sealed in packaging (closed storage) or in open beakers and exposed to the 80% relative humidity of the incubator they were kept in. Samples were subsequently taken from these treatments over a further 165 days to assess viability. Spores from the same production run were also used to test their persistence following application to three different substrates, clay, cement and wood, using a hand held sprayer. The experiments were conducted at two different institutes with one using adult female Anopheles stephensi and the other adult female Anopheles gambiae. Mosquitoes were exposed to the treated substrates for one hour before being removed and their survival monitored for the next 14 days. Assays were performed at monthly intervals over a maximum seven months. Results Spore storage under refrigeration resulted in no loss of spore viability over more than two years. Spore viability of those samples kept under open and closed storage was highly dependent on the incubation temperature with higher temperatures decreasing viability more rapidly than cooler temperatures. Mosquito survival following exposure was dependent on substrate type. Spore persistence on the clay substrate was greatest achieving 80% population reduction for four months against An. stephensi and for at least five months against Anopheles gambiae. Cement and wood substrates had more variable mortality with the highest spore persistence being two to three months for the two substrates respectively. Conclusions Spore shelf-life under refrigeration surpassed the standard two year shelf-life expected of a mosquito control product. Removal to a variety of temperatures under either closed or open storage indicated that samples sent out from refrigeration should be deployed rapidly in control operations to avoid loss of viability. Spore persistence following application onto clay surfaces was comparable to a number of chemical insecticides in common use. Persistence on cement and wood was shorter but in one assay still comparable to some organophosphate and pyrethroid insecticides. Optimized formulations could be expected to improve spore persistence still further.
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Affiliation(s)
- Simon Blanford
- Center for Infectious Disease Dynamics, Penn State University, Department of Biology, Mueller Laboratory, University Park, PA 16802, USA.
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Pan JY, Zhou SS, Zheng X, Huang F, Wang DQ, Shen YZ, Su YP, Zhou GC, Liu F, Jiang JJ. Vector capacity of Anopheles sinensis in malaria outbreak areas of central China. Parasit Vectors 2012; 5:136. [PMID: 22776520 PMCID: PMC3436673 DOI: 10.1186/1756-3305-5-136] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2012] [Accepted: 06/29/2012] [Indexed: 01/24/2023] Open
Abstract
BACKGROUND Both falciparum and vivax malaria were historically prevalent in China with high incidence. With the control efforts, the annual incidence in the whole country has reduced to 0.0001% except in some areas in the southern borders after 2000. Despite this, the re-emergence or outbreak of malaria was unavoidable in central China during 2005-2007. In order to understand the role of the vector in the transmission of malaria during the outbreak period, the vector capacity of An. sinensis in Huanghuai valley of central China was investigated. FINDINGS The study was undertaken in two sites, namely Huaiyuan county of Anhui province and Yongcheng county of Henan province. In each county, malaria cases were recorded for recent years, and transmission risk factors for each study village including anti-mosquito facilities and total number of livestock were recorded by visiting each household in the study sites. The specimens of mosquitoes were collected in two villages, and population density and species in each study site were recorded after the identification of different species, and the blood-fed mosquitoes were tested by ring precipitation test. Finally, various indicators were calculated to estimate vector capacity or dynamics, including mosquito biting rate (MBR), human blood index (HBI), and the parous rates (M). Finally, the vector capacity, as an important indicator of malaria transmission to predict the potential recurrence of malaria, was estimated and compared in each study site.About 93.0% of 80 households in Huaiyuan and 89.3% of 192 households in Yongcheng had anti-mosquito facilities. No cattle or pigs were found, only less than 10 sheep were found in each study village. A total of 94 and 107 Anopheles spp. mosquitos were captured in two study sites, respectively, and all of An. sinensis were morphologically identified. It was found that mosquito blood-feeding peak was between 9:00 pm and 12:00 pm. Man biting rate of An. sinensis was 6.0957 and 5.8621 (mosquitoes/people/night) estimated by using half-night human bait trap method and full-capture method, respectively. Human blood indexes (HBI) were 0.6667 (6/9) and 0.6429 (18/28), and man-biting habits were 0.2667 and 0.2572 in two sites, respectively. Therefore, the expectation of infective life and vector capacity of An. sinensis was 0.3649-0.4761 and 0.5502-0.7740, respectively, in Huanhuai valley of central China where the outbreak occurred, which is much higher than that in the previous years without malaria outbreak. CONCLUSIONS This study suggests that vivax malaria outbreak in Huanhuai valley is highly related to the enhancement in vector capacity of An. sinensis for P. vivax, which is attributed to the local residents' habits and the remarkable drop in the number of large livestock leading to disappearance of traditional biological barriers.
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Affiliation(s)
- Jia-Yun Pan
- National Institute of Parasitic Diseases, Chinese Center for Disease Control and Prevention, Shanghai, 200025, People’s Republic of China
- WHO Collaborating Centre for Malaria, Schistosomiasis and Filariasis, Key Laboratory of Parasite & Vector Biology, Ministry of Health, Shanghai, 200025, People’s Republic of China
| | - Shui-Sen Zhou
- National Institute of Parasitic Diseases, Chinese Center for Disease Control and Prevention, Shanghai, 200025, People’s Republic of China
- WHO Collaborating Centre for Malaria, Schistosomiasis and Filariasis, Key Laboratory of Parasite & Vector Biology, Ministry of Health, Shanghai, 200025, People’s Republic of China
| | - Xiang Zheng
- National Institute of Parasitic Diseases, Chinese Center for Disease Control and Prevention, Shanghai, 200025, People’s Republic of China
- WHO Collaborating Centre for Malaria, Schistosomiasis and Filariasis, Key Laboratory of Parasite & Vector Biology, Ministry of Health, Shanghai, 200025, People’s Republic of China
| | - Fang Huang
- National Institute of Parasitic Diseases, Chinese Center for Disease Control and Prevention, Shanghai, 200025, People’s Republic of China
- WHO Collaborating Centre for Malaria, Schistosomiasis and Filariasis, Key Laboratory of Parasite & Vector Biology, Ministry of Health, Shanghai, 200025, People’s Republic of China
| | - Duo-Quan Wang
- National Institute of Parasitic Diseases, Chinese Center for Disease Control and Prevention, Shanghai, 200025, People’s Republic of China
- WHO Collaborating Centre for Malaria, Schistosomiasis and Filariasis, Key Laboratory of Parasite & Vector Biology, Ministry of Health, Shanghai, 200025, People’s Republic of China
| | - Yu-Zu Shen
- Anhui Center for Disease Control and Prevention, Wuhu, 241000, People’s Republic of China
| | - Yun-Pu Su
- Henan Center for Disease Control and Prevention, Zhengzhou, 450016, People’s Republic of China
| | - Guang-Chao Zhou
- Yuangcheng Center for Disease Control and Prevention, Yuangchen, Henan province, 450000, People’s Republic of China
| | - Feng Liu
- Yongqiao District Center for Disease Control and Prevention, Shuzhou, Anhui province, 241000, People’s Republic of China
| | - Jing-Jing Jiang
- Anhui Center for Disease Control and Prevention, Wuhu, 241000, People’s Republic of China
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Mnyone LL, Lyimo IN, Lwetoijera DW, Mpingwa MW, Nchimbi N, Hancock PA, Russell TL, Kirby MJ, Takken W, Koenraadt CJM. Exploiting the behaviour of wild malaria vectors to achieve high infection with fungal biocontrol agents. Malar J 2012; 11:87. [PMID: 22449130 PMCID: PMC3337815 DOI: 10.1186/1475-2875-11-87] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2012] [Accepted: 03/26/2012] [Indexed: 12/20/2022] Open
Abstract
BACKGROUND Control of mosquitoes that transmit malaria has been the mainstay in the fight against the disease, but alternative methods are required in view of emerging insecticide resistance. Entomopathogenic fungi are candidate alternatives, but to date, few trials have translated the use of these agents to field-based evaluations of their actual impact on mosquito survival and malaria risk. Mineral oil-formulations of the entomopathogenic fungi Metarhizium anisopliae and Beauveria bassiana were applied using five different techniques that each exploited the behaviour of malaria mosquitoes when entering, host-seeking or resting in experimental huts in a malaria endemic area of rural Tanzania. RESULTS Survival of mosquitoes was reduced by 39-57% relative to controls after forcing upward house-entry of mosquitoes through fungus treated baffles attached to the eaves or after application of fungus-treated surfaces around an occupied bed net (bed net strip design). Moreover, 68 to 76% of the treatment mosquitoes showed fungal growth and thus had sufficient contact with fungus treated surfaces. A population dynamic model of malaria-mosquito interactions shows that these infection rates reduce malaria transmission by 75-80% due to the effect of fungal infection on adult mortality alone. The model also demonstrated that even if a high proportion of the mosquitoes exhibits outdoor biting behaviour, malaria transmission was still significantly reduced. CONCLUSIONS Entomopathogenic fungi strongly affect mosquito survival and have a high predicted impact on malaria transmission. These entomopathogens represent a viable alternative for malaria control, especially if they are used as part of an integrated vector management strategy.
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Affiliation(s)
- Ladslaus L Mnyone
- Biomedical and Environmental Group, Ifakara Health Institute, P.O. Box 53, Off Mlabani Passage, Ifakara, Tanzania
- Laboratory of Entomology, Wageningen University and Research Centre, P.O. Box 8031, 6700 EH Wageningen, The Netherlands
- Pest Management Centre, Sokoine University of Agriculture, P.O. Box 3110, Morogoro, Tanzania
| | - Issa N Lyimo
- Biomedical and Environmental Group, Ifakara Health Institute, P.O. Box 53, Off Mlabani Passage, Ifakara, Tanzania
- Faculty of Biomedical and Life Sciences, University of Glasgow, 120 University Place, G12 8TA Glasgow, UK
| | - Dickson W Lwetoijera
- Biomedical and Environmental Group, Ifakara Health Institute, P.O. Box 53, Off Mlabani Passage, Ifakara, Tanzania
| | - Monica W Mpingwa
- Biomedical and Environmental Group, Ifakara Health Institute, P.O. Box 53, Off Mlabani Passage, Ifakara, Tanzania
| | - Nuru Nchimbi
- Biomedical and Environmental Group, Ifakara Health Institute, P.O. Box 53, Off Mlabani Passage, Ifakara, Tanzania
| | | | - Tanya L Russell
- Biomedical and Environmental Group, Ifakara Health Institute, P.O. Box 53, Off Mlabani Passage, Ifakara, Tanzania
- The University of Queensland, School of Population Health, Australian Centre for Tropical and International Health, Brisbane 4006, Australia
- Vector Group, Liverpool School of Tropical Medicine, Liverpool L3 5QA, UK
| | - Matthew J Kirby
- Biomedical and Environmental Group, Ifakara Health Institute, P.O. Box 53, Off Mlabani Passage, Ifakara, Tanzania
- Laboratory of Entomology, Wageningen University and Research Centre, P.O. Box 8031, 6700 EH Wageningen, The Netherlands
| | - Willem Takken
- Laboratory of Entomology, Wageningen University and Research Centre, P.O. Box 8031, 6700 EH Wageningen, The Netherlands
| | - Constantianus JM Koenraadt
- Laboratory of Entomology, Wageningen University and Research Centre, P.O. Box 8031, 6700 EH Wageningen, The Netherlands
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Abdul-Ghani R, Al-Mekhlafi AM, Alabsi MS. Microbial control of malaria: biological warfare against the parasite and its vector. Acta Trop 2012; 121:71-84. [PMID: 22100545 DOI: 10.1016/j.actatropica.2011.11.001] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2011] [Revised: 10/31/2011] [Accepted: 11/04/2011] [Indexed: 01/31/2023]
Abstract
Microbial applications in malaria transmission control have drawn global attention. Mosquito midgut microbiota can modulate vector immunity and block Plasmodium development. Paratransgenic manipulation of bacterial symbionts and Wolbachia can affect reproductive characteristics of mosquitoes. Bacillus-based biolarvicides can control mosquito larvae in different breeding habitats, but their effectiveness differs according to the type of formulation applied, and the physical and ecological conditions of the environment. Entomopathogenic fungi show promise as effective and evolution-proof agents against adult mosquitoes. In addition, transgenic fungi can express anti-plasmodial effector molecules that can target the parasite inside its vector. Despite showing effectiveness in domestic environments as well as against insecticide-resistant mosquitoes, claims towards their deployability in the field and their possible use in integrated vector management programmes have yet to be investigated. Viral pathogens show efficacy in the interruption of sporogonic development of the parasite, and protozoal pathogens exert direct pathogenic potential on larvae and adults with substantial effects on mosquito longevity and fecundity. However, the technology required for their isolation and maintenance impedes their field application. Many agents show promising findings; however, the question remains about the epidemiologic reality of these approaches because even those that have been tried under field conditions still have certain limitations. This review addresses aspects of the microbial control of malaria between proof-of-concept and epidemiologic reality.
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Blanford S, Shi W, Christian R, Marden JH, Koekemoer LL, Brooke BD, Coetzee M, Read AF, Thomas MB. Lethal and pre-lethal effects of a fungal biopesticide contribute to substantial and rapid control of malaria vectors. PLoS One 2011; 6:e23591. [PMID: 21897846 PMCID: PMC3163643 DOI: 10.1371/journal.pone.0023591] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2011] [Accepted: 07/20/2011] [Indexed: 11/19/2022] Open
Abstract
Rapidly emerging insecticide resistance is creating an urgent need for new active ingredients to control the adult mosquitoes that vector malaria. Biopesticides based on the spores of entomopathogenic fungi have shown considerable promise by causing very substantial mortality within 7-14 days of exposure. This mortality will generate excellent malaria control if there is a high likelihood that mosquitoes contact fungi early in their adult lives. However, where contact rates are lower, as might result from poor pesticide coverage, some mosquitoes will contact fungi one or more feeding cycles after they acquire malaria, and so risk transmitting malaria before the fungus kills them. Critics have argued that 'slow acting' fungal biopesticides are, therefore, incapable of delivering malaria control in real-world contexts. Here, utilizing standard WHO laboratory protocols, we demonstrate effective action of a biopesticide much faster than previously reported. Specifically, we show that transient exposure to clay tiles sprayed with a candidate biopesticide comprising spores of a natural isolate of Beauveria bassiana, could reduce malaria transmission potential to zero within a feeding cycle. The effect resulted from a combination of high mortality and rapid fungal-induced reduction in feeding and flight capacity. Additionally, multiple insecticide-resistant lines from three key African malaria vector species were completely susceptible to fungus. Thus, fungal biopesticides can block transmission on a par with chemical insecticides, and can achieve this where chemical insecticides have little impact. These results support broadening the current vector control paradigm beyond fast-acting chemical toxins.
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Affiliation(s)
- Simon Blanford
- Center for Infectious Disease Dynamics, Mueller Laboratory, Department of Biology, Penn State University, University Park, Pennsylvania, United States of America
- Center for Infectious Disease Dynamics, Merkle Lab, Department of Entomology, Penn State University, University Park, Pennsylvania, United States of America
| | - Wangpeng Shi
- Center for Infectious Disease Dynamics, Merkle Lab, Department of Entomology, Penn State University, University Park, Pennsylvania, United States of America
- Key Laboratory for Biological Control, China Agricultural University, Ministry of Agriculture, Beijing, China
| | - Riann Christian
- Vector Control Reference Unit, National Institute for Communicable Diseases of the National Health Laboratory Service, Johannesburg, South Africa
- Malaria Entomology Research Unit, School of Pathology, Faculty of Health Sciences, University of Witwatersrand, Johannesburg, South Africa
| | - James H. Marden
- Department of Biology, Mueller Laboratory, Penn State University, University Park, Pennsylvania, United States of America
| | - Lizette L. Koekemoer
- Vector Control Reference Unit, National Institute for Communicable Diseases of the National Health Laboratory Service, Johannesburg, South Africa
- Malaria Entomology Research Unit, School of Pathology, Faculty of Health Sciences, University of Witwatersrand, Johannesburg, South Africa
| | - Basil D. Brooke
- Vector Control Reference Unit, National Institute for Communicable Diseases of the National Health Laboratory Service, Johannesburg, South Africa
- Malaria Entomology Research Unit, School of Pathology, Faculty of Health Sciences, University of Witwatersrand, Johannesburg, South Africa
| | - Maureen Coetzee
- Vector Control Reference Unit, National Institute for Communicable Diseases of the National Health Laboratory Service, Johannesburg, South Africa
- Malaria Entomology Research Unit, School of Pathology, Faculty of Health Sciences, University of Witwatersrand, Johannesburg, South Africa
| | - Andrew F. Read
- Center for Infectious Disease Dynamics, Mueller Laboratory, Department of Biology, Penn State University, University Park, Pennsylvania, United States of America
- Center for Infectious Disease Dynamics, Merkle Lab, Department of Entomology, Penn State University, University Park, Pennsylvania, United States of America
- Fogarty International Center, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Matthew B. Thomas
- Center for Infectious Disease Dynamics, Merkle Lab, Department of Entomology, Penn State University, University Park, Pennsylvania, United States of America
- Malaria Entomology Research Unit, School of Pathology, Faculty of Health Sciences, University of Witwatersrand, Johannesburg, South Africa
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George J, Blanford S, Domingue MJ, Thomas MB, Read AF, Baker TC. Reduction in host-finding behaviour in fungus-infected mosquitoes is correlated with reduction in olfactory receptor neuron responsiveness. Malar J 2011; 10:219. [PMID: 21812944 PMCID: PMC3162589 DOI: 10.1186/1475-2875-10-219] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2011] [Accepted: 08/03/2011] [Indexed: 11/08/2022] Open
Abstract
BACKGROUND Chemical insecticides against mosquitoes are a major component of malaria control worldwide. Fungal entomopathogens formulated as biopesticides and applied as insecticide residual sprays could augment current control strategies and mitigate the evolution of resistance to chemical-based insecticides. METHODS Anopheles stephensi mosquitoes were exposed to Beauveria bassiana or Metarhizium acridum fungal spores and sub-lethal effects of exposure to fungal infection were studied, especially the potential for reductions in feeding and host location behaviours related to olfaction. Electrophysiological techniques, such as electroantennogram, electropalpogram and single sensillum recording techniques were then employed to investigate how fungal exposure affected the olfactory responses in mosquitoes. RESULTS Exposure to B. bassiana caused significant mortality and reduced the propensity of mosquitoes to respond and fly to a feeding stimulus. Exposure to M. acridum spores induced a similar decline in feeding propensity, albeit more slowly than B. bassiana exposure. Reduced host-seeking responses following fungal exposure corresponded to reduced olfactory neuron responsiveness in both antennal electroantennogram and maxillary palp electropalpogram recordings. Single cell recordings from neurons on the palps confirmed that fungal-exposed behavioural non-responders exhibited significantly impaired responsiveness of neurons tuned specifically to 1-octen-3-ol and to a lesser degree, to CO2. CONCLUSIONS Fungal infection reduces the responsiveness of mosquitoes to host odour cues, both behaviourally and neuronally. These pre-lethal effects are likely to synergize with fungal-induced mortality to further reduce the capacity of mosquito populations exposed to fungal biopesticides to transmit malaria.
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Affiliation(s)
- Justin George
- Department of Entomology, Pennsylvania State University, University Park, PA 16802, USA
| | - Simon Blanford
- Department of Entomology, Pennsylvania State University, University Park, PA 16802, USA
- Center for Infectious Disease Dynamics, Pennsylvania State University, University Park, PA 16802, USA
| | - Michael J Domingue
- Department of Entomology, Pennsylvania State University, University Park, PA 16802, USA
| | - Matthew B Thomas
- Department of Entomology, Pennsylvania State University, University Park, PA 16802, USA
- Center for Infectious Disease Dynamics, Pennsylvania State University, University Park, PA 16802, USA
| | - Andrew F Read
- Department of Entomology, Pennsylvania State University, University Park, PA 16802, USA
- Center for Infectious Disease Dynamics, Pennsylvania State University, University Park, PA 16802, USA
| | - Thomas C Baker
- Department of Entomology, Pennsylvania State University, University Park, PA 16802, USA
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White MT, Griffin JT, Churcher TS, Ferguson NM, Basáñez MG, Ghani AC. Modelling the impact of vector control interventions on Anopheles gambiae population dynamics. Parasit Vectors 2011; 4:153. [PMID: 21798055 PMCID: PMC3158753 DOI: 10.1186/1756-3305-4-153] [Citation(s) in RCA: 150] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2011] [Accepted: 07/28/2011] [Indexed: 11/24/2022] Open
Abstract
Background Intensive anti-malaria campaigns targeting the Anopheles population have demonstrated substantial reductions in adult mosquito density. Understanding the population dynamics of Anopheles mosquitoes throughout their whole lifecycle is important to assess the likely impact of vector control interventions alone and in combination as well as to aid the design of novel interventions. Methods An ecological model of Anopheles gambiae sensu lato populations incorporating a rainfall-dependent carrying capacity and density-dependent regulation of mosquito larvae in breeding sites is developed. The model is fitted to adult mosquito catch and rainfall data from 8 villages in the Garki District of Nigeria (the 'Garki Project') using Bayesian Markov Chain Monte Carlo methods and prior estimates of parameters derived from the literature. The model is used to compare the impact of vector control interventions directed against adult mosquito stages - long-lasting insecticide treated nets (LLIN), indoor residual spraying (IRS) - and directed against aquatic mosquito stages, alone and in combination on adult mosquito density. Results A model in which density-dependent regulation occurs in the larval stages via a linear association between larval density and larval death rates provided a good fit to seasonal adult mosquito catches. The effective mosquito reproduction number in the presence of density-dependent regulation is dependent on seasonal rainfall patterns and peaks at the start of the rainy season. In addition to killing adult mosquitoes during the extrinsic incubation period, LLINs and IRS also result in less eggs being oviposited in breeding sites leading to further reductions in adult mosquito density. Combining interventions such as the application of larvicidal or pupacidal agents that target the aquatic stages of the mosquito lifecycle with LLINs or IRS can lead to substantial reductions in adult mosquito density. Conclusions Density-dependent regulation of anopheline larvae in breeding sites ensures robust, stable mosquito populations that can persist in the face of intensive vector control interventions. Selecting combinations of interventions that target different stages in the vector's lifecycle will result in maximum reductions in mosquito density.
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Affiliation(s)
- Michael T White
- MRC Centre for Outbreak Analysis & Modelling, Department of Infectious Disease Epidemiology, Imperial College London, London, UK.
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Hancock PA, Sinkins SP, Godfray HCJ. Population dynamic models of the spread of Wolbachia. Am Nat 2011; 177:323-33. [PMID: 21460541 DOI: 10.1086/658121] [Citation(s) in RCA: 84] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
Wolbachia are endosymbionts that are found in many insect species and can spread rapidly when introduced into a naive host population. Most Wolbachia spread when their infection frequency exceeds a threshold normally calculated using purely population genetic models. However, spread may also depend on the population dynamics of the insect host. We develop models to explore interactions between host population dynamics and Wolbachia infection frequency for an age-structured insect population regulated by larval density dependence. We first derive a new expression for the threshold frequency that extends existing theory to incorporate important details of the insect's life history. In the presence of immigration and emigration, the threshold also depends on the form of density-dependent regulation. We show how the type of immigration (constant or pulsed) and the temporal dynamics of the host population can strongly affect the spread of Wolbachia. The results help understand the natural dynamics of Wolbachia infections and aid the design of programs to introduce Wolbachia to control insects that are disease vectors or pests.
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Lorenz LM, Koella JC. The microsporidian parasite Vavraia culicis as a potential late life-acting control agent of malaria. Evol Appl 2011; 4:783-90. [PMID: 25568022 PMCID: PMC3352544 DOI: 10.1111/j.1752-4571.2011.00199.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2011] [Accepted: 06/14/2011] [Indexed: 01/16/2023] Open
Abstract
Microsporidian parasites are being considered as alternatives to conventional insecticides for malaria control. They should reduce malaria transmission by shortening the lifespan of female mosquitoes and thus killing them before they transmit malaria. As the parasite replicates throughout the mosquito's life, it should have little detrimental effects on young mosquitoes, thus putting less selection pressure on the hosts to evolve resistance. Here, we examined these expectations for the microsporidian Vavraia culicis on Anopheles gambiae Giles sensu stricto mosquitoes under varying environmental conditions. Infection by the microsporidian delayed pupation by 10%, decreased fecundity by 23% and reduced adult lifespan by 27%, with higher infectious doses causing greater effects. The decrease of lifespan was mostly because of an increase of the mortality rate with age. Similarly, the parasite's effect on mosquito fecundity increased with the mosquitoes’ age. Neither infection nor food availability affected juvenile survival. Thus, as V. culicis reduced the longevity of A. gambiae (s.s.), yet affected mortality and fecundity of the young mosquitoes only slightly, the microsporidian is a promising alternative to insecticides for effective malaria control that will impose little evolutionary pressure for resistance.
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Affiliation(s)
- Lena M Lorenz
- Division of Biology, Imperial College London Silwood Park Campus, Ascot, UK ; Department of Disease Control, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine London, UK
| | - Jacob C Koella
- Division of Biology, Imperial College London Silwood Park Campus, Ascot, UK
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Hancock PA, Sinkins SP, Godfray HCJ. Strategies for introducing Wolbachia to reduce transmission of mosquito-borne diseases. PLoS Negl Trop Dis 2011; 5:e1024. [PMID: 21541357 PMCID: PMC3082501 DOI: 10.1371/journal.pntd.0001024] [Citation(s) in RCA: 83] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2010] [Accepted: 02/16/2011] [Indexed: 11/18/2022] Open
Abstract
Certain strains of the endosymbiont Wolbachia have the potential to lower the vectorial capacity of mosquito populations and assist in controlling a number of mosquito-borne diseases. An important consideration when introducing Wolbachia-carrying mosquitoes into natural populations is the minimisation of any transient increase in disease risk or biting nuisance. This may be achieved by predominantly releasing male mosquitoes. To explore this, we use a sex-structured model of Wolbachia-mosquito interactions. We first show that Wolbachia spread can be initiated with very few infected females provided the infection frequency in males exceeds a threshold. We then consider realistic introduction scenarios involving the release of batches of infected mosquitoes, incorporating seasonal fluctuations in population size. For a range of assumptions about mosquito population dynamics we find that male-biased releases allow the infection to spread after the introduction of low numbers of females, many fewer than with equal sex-ratio releases. We extend the model to estimate the transmission rate of a mosquito-borne pathogen over the course of Wolbachia establishment. For a range of release strategies we demonstrate that male-biased release of Wolbachia-infected mosquitoes can cause substantial transmission reductions without transiently increasing disease risk. The results show the importance of including mosquito population dynamics in studying Wolbachia spread and that male-biased releases can be an effective and safe way of rapidly establishing the symbiont in mosquito populations.
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Farenhorst M, Hilhorst A, Thomas MB, Knols BGJ. Development of fungal applications on netting substrates for malaria vector control. JOURNAL OF MEDICAL ENTOMOLOGY 2011; 48:305-313. [PMID: 21485366 DOI: 10.1603/me10134] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Mosquito resistance to chemical insecticides is considered a serious threat for the sustainable use of contemporary malaria vector control methods. Fungal entomopathogens show potential as alternative biological control agents against (insecticide-resistant) anophelines. This study was designed to test whether the fungus, Beauveria bassiana, could be delivered to mosquitoes on netting materials that might be used in house screens, such as eave curtains. Tests were conducted to determine effects of formulation, application method, netting material, and nature of mosquito contact. Beauveria had a twice as high impact on Anopheles gambiae s.s. longevity when suspended in Shellsol solvent compared with Ondina oil (HR = 2.12, 95% confidence interval = 1.83-2.60, P < 0.001), and was significantly more infective when applied through spraying than dipping. Polyester and cotton bednets were the most effective substrates for mosquito infections, with highest spore viability on cotton nets. Whereas fungal impact was highest in mosquitoes that had passed through large-meshed impregnated nets, overall efficacy was equal between small- and large-meshed nets, with < or = 30-min spore contact killing >90% of mosquitoes within 10 d. Results indicate that the use of fungal spores dissolved in Shellsol and sprayed on small-meshed cotton eave curtain nets would be the most promising option for field implementation. Biological control with fungus-impregnated eave curtains could provide a means to target host-seeking mosquitoes upon house entry, and has potential for use in integrated vector management strategies, in combination with chemical vector control measures, to supplement malaria control in areas with high levels of insecticide resistance.
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Affiliation(s)
- Marit Farenhorst
- Laboratory of Entomology, Wageningen University and Research Centre, P.O. Box 8031, 6700 EH, Wageningen, The Netherlands.
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Fang W, Vega-Rodríguez J, Ghosh AK, Jacobs-Lorena M, Kang A, St. Leger RJ. Development of transgenic fungi that kill human malaria parasites in mosquitoes. Science 2011; 331:1074-7. [PMID: 21350178 PMCID: PMC4153607 DOI: 10.1126/science.1199115] [Citation(s) in RCA: 172] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Metarhizium anisopliae infects mosquitoes through the cuticle and proliferates in the hemolymph. To allow M. anisopliae to combat malaria in mosquitoes with advanced malaria infections, we produced recombinant strains expressing molecules that target sporozoites as they travel through the hemolymph to the salivary glands. Eleven days after a Plasmodium-infected blood meal, mosquitoes were treated with M. anisopliae expressing salivary gland and midgut peptide 1 (SM1), which blocks attachment of sporozoites to salivary glands; a single-chain antibody that agglutinates sporozoites; or scorpine, which is an antimicrobial toxin. These reduced sporozoite counts by 71%, 85%, and 90%, respectively. M. anisopliae expressing scorpine and an [SM1](8):scorpine fusion protein reduced sporozoite counts by 98%, suggesting that Metarhizium-mediated inhibition of Plasmodium development could be a powerful weapon for combating malaria.
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Affiliation(s)
- Weiguo Fang
- Department of Entomology, University of Maryland, 4112 Plant Sciences Building, College Park, MD 20742, USA
| | - Joel Vega-Rodríguez
- Malaria Research Institute, Department of Molecular Microbiology and Immunology, Johns Hopkins School of Public Health, 615 North Wolfe Street, E5132, Baltimore, MD 21205, USA
| | - Anil K. Ghosh
- Malaria Research Institute, Department of Molecular Microbiology and Immunology, Johns Hopkins School of Public Health, 615 North Wolfe Street, E5132, Baltimore, MD 21205, USA
| | - Marcelo Jacobs-Lorena
- Malaria Research Institute, Department of Molecular Microbiology and Immunology, Johns Hopkins School of Public Health, 615 North Wolfe Street, E5132, Baltimore, MD 21205, USA
| | - Angray Kang
- Antibody Technology Group, Department of Molecular and Applied Biosciences, School of Life Sciences, University of Westminster, 115 New Cavendish Street, London W1W 6UW, UK
| | - Raymond J. St. Leger
- Department of Entomology, University of Maryland, 4112 Plant Sciences Building, College Park, MD 20742, USA
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Bukhari T, Takken W, Koenraadt CJM. Development of Metarhizium anisopliae and Beauveria bassiana formulations for control of malaria mosquito larvae. Parasit Vectors 2011; 4:23. [PMID: 21342492 PMCID: PMC3051916 DOI: 10.1186/1756-3305-4-23] [Citation(s) in RCA: 90] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2010] [Accepted: 02/22/2011] [Indexed: 12/05/2022] Open
Abstract
Background The entomopathogenic fungi Metarhizium anisopliae and Beauveria bassiana have demonstrated effectiveness against anopheline larvae in the laboratory. However, utilising these fungi for the control of anopheline larvae under field conditions, relies on development of effective means of application as well as reducing their sensitivity to UV radiation, high temperatures and the inevitable contact with water. This study was conducted to develop formulations that facilitate the application of Metarhizium anisopliae and Beauveria bassiana spores for the control of anopheline larvae, and also improve their persistence under field conditions. Methods Laboratory bioassays were conducted to test the ability of aqueous (0.1% Tween 80), dry (organic and inorganic) and oil (mineral and synthetic) formulations to facilitate the spread of fungal spores over the water surface and improve the efficacy of formulated spores against anopheline larvae as well as improve spore survival after application. Field bioassays were then carried out to test the efficacy of the most promising formulation under field conditions in western Kenya. Results When formulated in a synthetic oil (ShellSol T), fungal spores of both Metarhizium anisopliae and Beauveria bassiana were easy to mix and apply to the water surface. This formulation was more effective against anopheline larvae than 0.1% Tween 80, dry powders or mineral oil formulations. ShellSol T also improved the persistence of fungal spores after application to the water. Under field conditions in Kenya, the percentage pupation of An. gambiae was significantly reduced by 39 - 50% by the ShellSol T-formulated Metarhizium anisopliae and Beauveria bassiana spores as compared to the effects of the application of unformulated spores. Conclusions ShellSol T is an effective carrier for fungal spores when targeting anopheline larvae under both laboratory and field conditions. Entomopathogenic fungi formulated with a suitable carrier are a promising tool for control of larval populations of malaria mosquitoes. Additional studies are required to identify the best delivery method (where, when and how) to make use of the entomopathogenic potential of these fungi against anopheline larvae.
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Affiliation(s)
- Tullu Bukhari
- Laboratory of Entomology, Wageningen University, Wageningen, The Netherlands.
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A reaction–diffusion malaria model with incubation period in the vector population. J Math Biol 2010; 62:543-68. [DOI: 10.1007/s00285-010-0346-8] [Citation(s) in RCA: 137] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2009] [Revised: 04/01/2010] [Indexed: 10/19/2022]
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Bellan SE. The importance of age dependent mortality and the extrinsic incubation period in models of mosquito-borne disease transmission and control. PLoS One 2010; 5:e10165. [PMID: 20405010 PMCID: PMC2854142 DOI: 10.1371/journal.pone.0010165] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2009] [Accepted: 03/13/2010] [Indexed: 11/20/2022] Open
Abstract
Nearly all mathematical models of vector-borne diseases have assumed that vectors die at constant rates. However, recent empirical research suggests that mosquito mortality rates are frequently age dependent. This work develops a simple mathematical model to assess how relaxing the classical assumption of constant mortality affects the predicted effectiveness of anti-vectorial interventions. The effectiveness of mosquito control when mosquitoes die at age dependent rates was also compared across different extrinsic incubation periods. Compared to a more realistic age dependent model, constant mortality models overestimated the sensitivity of disease transmission to interventions that reduce mosquito survival. Interventions that reduce mosquito survival were also found to be slightly less effective when implemented in systems with shorter EIPs. Future transmission models that examine anti-vectorial interventions should incorporate realistic age dependent mortality rates.
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Affiliation(s)
- Steve E Bellan
- Department of Environmental Science, Policy and Management, University of California, Berkeley, California, United States of America.
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Kikankie CK, Brooke BD, Knols BGJ, Koekemoer LL, Farenhorst M, Hunt RH, Thomas MB, Coetzee M. The infectivity of the entomopathogenic fungus Beauveria bassiana to insecticide-resistant and susceptible Anopheles arabiensis mosquitoes at two different temperatures. Malar J 2010; 9:71. [PMID: 20210990 PMCID: PMC2839986 DOI: 10.1186/1475-2875-9-71] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2009] [Accepted: 03/08/2010] [Indexed: 11/28/2022] Open
Abstract
Background Control of the major African malaria vector species continues to rely extensively on the application of residual insecticides through indoor house spraying or bed net impregnation. Insecticide resistance is undermining the sustainability of these control strategies. Alternatives to the currently available conventional chemical insecticides are, therefore, urgently needed. Use of fungal pathogens as biopesticides is one such possibility. However, one of the challenges to the approach is the potential influence of varied environmental conditions and target species that could affect the efficacy of a biological 'active ingredient'. An initial investigation into this was carried out to assess the susceptibility of insecticide-susceptible and resistant laboratory strains and wild-collected Anopheles arabiensis mosquitoes to infection with the fungus Beauveria bassiana under two different laboratory temperature regimes. Methods Insecticide susceptibility to all four classes of insecticides recommended by WHO for vector control was tested on laboratory and wild-caught An. arabiensis, using standard WHO bioassay protocols. Mosquito susceptibility to fungus infection was tested using dry spores of B. bassiana under two temperature regimes (21 ± 1°C or 25 ± 2°C) representative of indoor conditions observed in western Kenya. Cox regression analysis was used to assess the effect of fungal infection on mosquito survival and the effect of insecticide resistance status and temperature on mortality rates following fungus infection. Results Survival data showed no relationship between insecticide susceptibility and susceptibility to B. bassiana. All tested colonies showed complete susceptibility to fungal infection despite some showing high resistance levels to chemical insecticides. There was, however, a difference in fungus-induced mortality rates between temperature treatments with virulence significantly higher at 25°C than 21°C. Even so, because malaria parasite development is also known to slow as temperatures fall, expected reductions in malaria transmission potential due to fungal infection under the cooler conditions would still be high. Conclusions These results provide evidence that the entomopathogenic fungus B. bassiana has potential for use as an alternative vector control tool against insecticide-resistant mosquitoes under conditions typical of indoor resting environments. Nonetheless, the observed variation in effective virulence reveals the need for further study to optimize selection of isolates, dose and use strategy in different eco-epidemiological settings.
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Affiliation(s)
- Christophe K Kikankie
- School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Johannesburg, South Africa
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Mnyone LL, Kirby MJ, Lwetoijera DW, Mpingwa MW, Knols BGJ, Takken W, Russell TL. Infection of the malaria mosquito, Anopheles gambiae, with two species of entomopathogenic fungi: effects of concentration, co-formulation, exposure time and persistence. Malar J 2009; 8:309. [PMID: 20030834 PMCID: PMC2808315 DOI: 10.1186/1475-2875-8-309] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2009] [Accepted: 12/23/2009] [Indexed: 01/26/2023] Open
Abstract
Background Entomopathogenic fungi Metarhizium anisopliae and Beauveria bassiana isolates have been shown to infect and reduce the survival of mosquito vectors. Methods Here four different bioassays were conducted to study the effect of conidia concentration, co-formulation, exposure time and persistence of the isolates M. anisopliae ICIPE-30 and B. bassiana I93-925 on infection and survival rates of female Anopheles gambiae sensu stricto. Test concentrations and exposure times ranged between 1 × 107 - 4 × 1010 conidia m-2 and 15 min - 6 h. In co-formulations, 2 × 1010 conidia m-2 of both fungus isolates were mixed at ratios of 4:1, 2:1, 1:1,1:0, 0:1, 1:2 and 1:4. To determine persistence, mosquitoes were exposed to surfaces treated 1, 14 or 28 d previously, with conidia concentrations of 2 × 109, 2 × 1010 or 4 × 1010. Results Mosquito survival varied with conidia concentration; 2 × 1010 conidia m-2 was the concentration above which no further reductions in survival were detectable for both isolates of fungus. The survival of mosquitoes exposed to single and co-formulated treatments was similar and no synergistic or additive effects were observed. Mosquitoes were infected within 30 min and longer exposure times did not result in a more rapid killing effect. Fifteen min exposure still achieved considerable mortality rates (100% mortality by 14 d) of mosquitoes, but at lower speed than with 30 min exposure (100% mortality by 9 d). Conidia remained infective up to 28 d post-application but higher concentrations did not increase persistence. Conclusion Both fungus isolates are effective and persistent at low concentrations and short exposure times.
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Affiliation(s)
- Ladslaus L Mnyone
- Biomedical and Environmental Group, Ifakara Health Institute, PO Box 53, Off Mlabani Passage, Ifakara, Tanzania.
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Dawes EJ, Churcher TS, Zhuang S, Sinden RE, Basáñez MG. Anopheles mortality is both age- and Plasmodium-density dependent: implications for malaria transmission. Malar J 2009; 8:228. [PMID: 19822012 PMCID: PMC2770541 DOI: 10.1186/1475-2875-8-228] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2009] [Accepted: 10/12/2009] [Indexed: 01/20/2023] Open
Abstract
Background Daily mortality is an important determinant of a vector's ability to transmit pathogens. Original simplifying assumptions in malaria transmission models presume vector mortality is independent of age, infection status and parasite load. Previous studies illustrate conflicting evidence as to the importance of Plasmodium-induced vector mortality, but very few studies to date have considered the effect of infection density on mosquito survival. Methods A series of three experiments were conducted, each consisting of four cages of 400-1,000 Anopheles stephensi mosquitoes fed on blood infected with different Plasmodium berghei ookinete densities per microlitre of blood. Twice daily the numbers of dead mosquitoes in each group were recorded, and on alternate days a sample of live mosquitoes from each group were dissected to determine parasite density in both midgut and salivary glands. Results Survival analyses indicate that mosquito mortality is both age- and infection intensity-dependent. Mosquitoes experienced an initially high, partly feeding-associated, mortality rate, which declined to a minimum before increasing with mosquito age and parasite intake. As a result, the life expectancy of a mosquito is shown to be dependent on both insect age and the density of Plasmodium infection. Conclusion These results contribute to understanding in greater detail the processes that influence sporogony in the mosquito, indicate the impact that parasite density could have on malaria transmission dynamics, and have implications for the design, development, and evaluation of transmission-blocking strategies.
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Affiliation(s)
- Emma J Dawes
- Department of Infectious Disease Epidemiology, Faculty of Medicine, Imperial College London, London, UK.
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Combining fungal biopesticides and insecticide-treated bednets to enhance malaria control. PLoS Comput Biol 2009; 5:e1000525. [PMID: 19798436 PMCID: PMC2742557 DOI: 10.1371/journal.pcbi.1000525] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2009] [Accepted: 08/31/2009] [Indexed: 11/19/2022] Open
Abstract
In developing strategies to control malaria vectors, there is increased interest in biological methods that do not cause instant vector mortality, but have sublethal and lethal effects at different ages and stages in the mosquito life cycle. These techniques, particularly if integrated with other vector control interventions, may produce substantial reductions in malaria transmission due to the total effect of alterations to multiple life history parameters at relevant points in the life-cycle and transmission-cycle of the vector. To quantify this effect, an analytically tractable gonotrophic cycle model of mosquito-malaria interactions is developed that unites existing continuous and discrete feeding cycle approaches. As a case study, the combined use of fungal biopesticides and insecticide treated bednets (ITNs) is considered. Low values of the equilibrium EIR and human prevalence were obtained when fungal biopesticides and ITNs were combined, even for scenarios where each intervention acting alone had relatively little impact. The effect of the combined interventions on the equilibrium EIR was at least as strong as the multiplicative effect of both interventions. For scenarios representing difficult conditions for malaria control, due to high transmission intensity and widespread insecticide resistance, the effect of the combined interventions on the equilibrium EIR was greater than the multiplicative effect, as a result of synergistic interactions between the interventions. Fungal biopesticide application was found to be most effective when ITN coverage was high, producing significant reductions in equilibrium prevalence for low levels of biopesticide coverage. By incorporating biological mechanisms relevant to vectorial capacity, continuous-time vector population models can increase their applicability to integrated vector management.
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