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Connolly JB, Burt A, Christophides G, Diabate A, Habtewold T, Hancock PA, James AA, Kayondo JK, Lwetoijera DW, Manjurano A, McKemey AR, Santos MR, Windbichler N, Randazzo F. Considerations for first field trials of low-threshold gene drive for malaria vector control. Malar J 2024; 23:156. [PMID: 38773487 PMCID: PMC11110314 DOI: 10.1186/s12936-024-04952-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2023] [Accepted: 04/15/2024] [Indexed: 05/23/2024] Open
Abstract
Sustainable reductions in African malaria transmission require innovative tools for mosquito control. One proposal involves the use of low-threshold gene drive in Anopheles vector species, where a 'causal pathway' would be initiated by (i) the release of a gene drive system in target mosquito vector species, leading to (ii) its transmission to subsequent generations, (iii) its increase in frequency and spread in target mosquito populations, (iv) its simultaneous propagation of a linked genetic trait aimed at reducing vectorial capacity for Plasmodium, and (v) reduced vectorial capacity for parasites in target mosquito populations as the gene drive system reaches fixation in target mosquito populations, causing (vi) decreased malaria incidence and prevalence. Here the scope, objectives, trial design elements, and approaches to monitoring for initial field releases of such gene dive systems are considered, informed by the successful implementation of field trials of biological control agents, as well as other vector control tools, including insecticides, Wolbachia, larvicides, and attractive-toxic sugar bait systems. Specific research questions to be addressed in initial gene drive field trials are identified, and adaptive trial design is explored as a potentially constructive and flexible approach to facilitate testing of the causal pathway. A fundamental question for decision-makers for the first field trials will be whether there should be a selective focus on earlier points of the pathway, such as genetic efficacy via measurement of the increase in frequency and spread of the gene drive system in target populations, or on wider interrogation of the entire pathway including entomological and epidemiological efficacy. How and when epidemiological efficacy will eventually be assessed will be an essential consideration before decisions on any field trial protocols are finalized and implemented, regardless of whether initial field trials focus exclusively on the measurement of genetic efficacy, or on broader aspects of the causal pathway. Statistical and modelling tools are currently under active development and will inform such decisions on initial trial design, locations, and endpoints. Collectively, the considerations here advance the realization of developer ambitions for the first field trials of low-threshold gene drive for malaria vector control within the next 5 years.
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Affiliation(s)
- John B Connolly
- Department of Life Sciences, Silwood Park, Imperial College London, London, UK.
| | - Austin Burt
- Department of Life Sciences, Silwood Park, Imperial College London, London, UK
| | - George Christophides
- Department of Life Sciences, South Kensington Campus, Imperial College London, London, UK
| | - Abdoulaye Diabate
- Institut de Recherche en Sciences de la Santé/Centre Muraz, Bobo-Dioulasso, Burkina Faso
| | - Tibebu Habtewold
- Department of Life Sciences, South Kensington Campus, Imperial College London, London, UK
- Environmental Health and Ecological Science Department, Ifakara Health Institute, Ifakara, Tanzania
| | - Penelope A Hancock
- MRC Centre for Global Infectious Disease Analysis, St. Mary's Campus, Imperial College London, London, UK
| | - Anthony A James
- Departments of Microbiology & Molecular Genetics and Molecular Biology & Biochemistry, University of California, Irvine, USA
| | - Jonathan K Kayondo
- Entomology Department, Uganda Virus Research Institute (UVRI), Entebbe, Uganda
| | | | - Alphaxard Manjurano
- Malaria Research Unit and Laboratory Sciences, Mwanza Medical Research Centre, National Institute for Medical Research, Mwanza, Tanzania
| | - Andrew R McKemey
- Department of Life Sciences, Silwood Park, Imperial College London, London, UK
| | - Michael R Santos
- Foundation for the National Institutes of Health, North Bethesda, MD, USA
| | - Nikolai Windbichler
- Department of Life Sciences, South Kensington Campus, Imperial College London, London, UK
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Yu Q, Qu Y, Zhang L, Yao X, Yang J, Chen S, Liu H, Wang Q, Wu M, Tao J, Zhou C, Alage IL, Liu S. Spatial spillovers of violent conflict amplify the impacts of climate variability on malaria risk in sub-Saharan Africa. Proc Natl Acad Sci U S A 2024; 121:e2309087121. [PMID: 38557184 PMCID: PMC11009658 DOI: 10.1073/pnas.2309087121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2023] [Accepted: 02/02/2024] [Indexed: 04/04/2024] Open
Abstract
Africa carries a disproportionately high share of the global malaria burden, accounting for 94% of malaria cases and deaths worldwide in 2019. It is also a politically unstable region and the most vulnerable continent to climate change in recent decades. Knowledge about the modifying impacts of violent conflict on climate-malaria relationships remains limited. Here, we quantify the associations between violent conflict, climate variability, and malaria risk in sub-Saharan Africa using health surveys from 128,326 individuals, historical climate data, and 17,429 recorded violent conflicts from 2006 to 2017. We observe that spatial spillovers of violent conflict (SSVCs) have spatially distant effects on malaria risk. Malaria risk induced by SSVCs within 50 to 100 km from the households gradually increases from 0.1% (not significant, P>0.05) to 6.5% (95% CI: 0 to 13.0%). SSVCs significantly promote malaria risk within the average 20.1 to 26.9 °C range. At the 12-mo mean temperature of 22.5 °C, conflict deaths have the largest impact on malaria risk, with an approximately 5.8% increase (95% CI: 1.0 to 11.0%). Additionally, a pronounced association between SSVCs and malaria risk exists in the regions with 9.2 wet days per month. The results reveal that SSVCs increase population exposure to harsh environments, amplifying the effect of warm temperature and persistent precipitation on malaria transmission. Violent conflict therefore poses a substantial barrier to mosquito control and malaria elimination efforts in sub-Saharan Africa. Our findings support effective targeting of treatment programs and vector control activities in conflict-affected regions with a high malaria risk.
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Affiliation(s)
- Qiwei Yu
- Department of Geography, State Key Laboratory of Remote Sensing Science, Faculty of Geographical Science, Beijing Normal University, Beijing100875, China
| | - Ying Qu
- Department of Geography, State Key Laboratory of Remote Sensing Science, Faculty of Geographical Science, Beijing Normal University, Beijing100875, China
| | - Liqiang Zhang
- Department of Geography, State Key Laboratory of Remote Sensing Science, Faculty of Geographical Science, Beijing Normal University, Beijing100875, China
| | - Xin Yao
- Department of Geography, State Key Laboratory of Remote Sensing Science, Faculty of Geographical Science, Beijing Normal University, Beijing100875, China
| | - Jing Yang
- Department of Geography, State Key Laboratory of Remote Sensing Science, Faculty of Geographical Science, Beijing Normal University, Beijing100875, China
| | - Siyuan Chen
- Department of Geography, State Key Laboratory of Remote Sensing Science, Faculty of Geographical Science, Beijing Normal University, Beijing100875, China
| | - Hui Liu
- Department of Geography, State Key Laboratory of Remote Sensing Science, Faculty of Geographical Science, Beijing Normal University, Beijing100875, China
| | - Qihao Wang
- Department of Geography, State Key Laboratory of Remote Sensing Science, Faculty of Geographical Science, Beijing Normal University, Beijing100875, China
| | - Mengfan Wu
- Department of Geography, State Key Laboratory of Remote Sensing Science, Faculty of Geographical Science, Beijing Normal University, Beijing100875, China
| | - Junpei Tao
- Department of Geography, State Key Laboratory of Remote Sensing Science, Faculty of Geographical Science, Beijing Normal University, Beijing100875, China
| | - Chenghu Zhou
- State Key Laboratory of Resources and Environmental Information System, Institute of Geographical Science and Natural Resources, Chinese Academy of Sciences, Beijing100101, China
| | - Isiaka Lukman Alage
- Space Research and Development Division, African Regional Centre for Space Science and Technology Education in English Ile ife, Ile ife, Osun220282, Nigeria
| | - Suhong Liu
- Department of Geography, State Key Laboratory of Remote Sensing Science, Faculty of Geographical Science, Beijing Normal University, Beijing100875, China
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Mwima R, Hui TYJ, Nanteza A, Burt A, Kayondo JK. Potential persistence mechanisms of the major Anopheles gambiae species complex malaria vectors in sub-Saharan Africa: a narrative review. Malar J 2023; 22:336. [PMID: 37936194 PMCID: PMC10631165 DOI: 10.1186/s12936-023-04775-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2023] [Accepted: 10/30/2023] [Indexed: 11/09/2023] Open
Abstract
The source of malaria vector populations that re-establish at the beginning of the rainy season is still unclear yet knowledge of mosquito behaviour is required to effectively institute control measures. Alternative hypotheses like aestivation, local refugia, migration between neighbouring sites, and long-distance migration (LDM) are stipulated to support mosquito persistence. This work assessed the malaria vector persistence dynamics and examined various studies done on vector survival via these hypotheses; aestivation, local refugia, local or long-distance migration across sub-Saharan Africa, explored a range of methods used, ecological parameters and highlighted the knowledge trends and gaps. The results about a particular persistence mechanism that supports the re-establishment of Anopheles gambiae, Anopheles coluzzii or Anopheles arabiensis in sub-Saharan Africa were not conclusive given that each method used had its limitations. For example, the Mark-Release-Recapture (MRR) method whose challenge is a low recapture rate that affects its accuracy, and the use of time series analysis through field collections whose challenge is the uncertainty about whether not finding mosquitoes during the dry season is a weakness of the conventional sampling methods used or because of hidden shelters. This, therefore, calls for further investigations emphasizing the use of ecological experiments under controlled conditions in the laboratory or semi-field, and genetic approaches, as they are known to complement each other. This review, therefore, unveils and assesses the uncertainties that influence the different malaria vector persistence mechanisms and provides recommendations for future studies.
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Affiliation(s)
- Rita Mwima
- Department of Entomology, Uganda Virus Research Institute (UVRI), Entebbe, Uganda
- Department of Biotechnical and Diagnostic Sciences, College of Veterinary Medicine, Animal Resources and Biosecurity (COVAB), Makerere University, Kampala, Uganda
| | - Tin-Yu J Hui
- Silwood Park Campus, Department of Life Sciences, Imperial College London, Ascot, UK
| | - Ann Nanteza
- Department of Biotechnical and Diagnostic Sciences, College of Veterinary Medicine, Animal Resources and Biosecurity (COVAB), Makerere University, Kampala, Uganda
| | - Austin Burt
- Silwood Park Campus, Department of Life Sciences, Imperial College London, Ascot, UK
| | - Jonathan K Kayondo
- Department of Entomology, Uganda Virus Research Institute (UVRI), Entebbe, Uganda.
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Abstract
Diapause, a stage-specific developmental arrest, is widely exploited by insects to bridge unfavorable seasons. Considerable progress has been made in understanding the ecology, physiology and evolutionary implications of insect diapause, yet intriguing questions remain. A more complete understanding of diapause processes on Earth requires a better geographic spread of investigations, including more work in the tropics and at high latitudes. Questions surrounding energy management and trade-offs between diapause and non-diapause remain understudied. We know little about how maternal effects direct the diapause response, and regulators of prolonged diapause are also poorly understood. Numerous factors that were recently linked to diapause are still waiting to be placed in the regulatory network leading from photoreception to engagement of the diapause program. These factors include epigenetic processes and small noncoding RNAs, and emerging data also suggest a role for the microbiome in diapause regulation. Another intriguing feature of diapause is the complexity of the response, resulting in a diverse suite of responses that comprise the diapause syndrome. Select transcription factors likely serve as master switches turning on these diverse responses, but we are far from understanding the full complexity. The richness of species displaying diapause offers a platform for seeking common components of a 'diapause toolbox'. Across latitudes, during invasion events and in a changing climate, diapause offers grand opportunities to probe evolutionary change and speciation. At a practical level, diapause responses can be manipulated for insect control and long-term storage. Diapausing insects also contain a treasure trove of pharmacological compounds and offer promising models for human health.
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Affiliation(s)
- David L Denlinger
- Departments of Entomology and Evolution, Ecology and Organismal Biology, Ohio State University, Columbus, OH 43210, USA
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Dried out but alive: how mosquitoes survive 8 months. Trends Parasitol 2023; 39:1-3. [PMID: 36470782 DOI: 10.1016/j.pt.2022.11.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2022] [Accepted: 11/21/2022] [Indexed: 12/05/2022]
Abstract
How malaria mosquitoes persist during the dry season in the Sahel and rapidly rebound at the onset of rains is unclear. Recently, Faiman and colleagues demonstrated that aestivation, a summer dormancy mechanism, is a major persistence strategy of Anopheles mosquitoes, which could be targeted by vector control.
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Resolving malaria's dry-season dilemma. Nat Ecol Evol 2022; 6:1593-1594. [PMID: 36216904 DOI: 10.1038/s41559-022-01832-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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