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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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Agumba S, Moshi V, Muchoki M, Omondi S, Kosgei J, Walker ED, Abong'o B, Achee N, Grieco J, Ochomo E. Experimental hut and field evaluation of a metofluthrin-based spatial repellent against pyrethroid-resistant Anopheles funestus in Siaya County, western Kenya. Parasit Vectors 2024; 17:6. [PMID: 38178213 PMCID: PMC10768102 DOI: 10.1186/s13071-023-06096-2] [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: 09/12/2023] [Accepted: 12/12/2023] [Indexed: 01/06/2024] Open
Abstract
BACKGROUND Spatial repellents (SR) may complement current vector control tools and provide additional coverage when people are not under their bednets or are outdoors. Here we assessed the efficacy of a metofluthrin-based SR in reducing exposure to pyrethroid-resistant Anopheles funestus in Siaya County, western Kenya. METHODS Metofluthrin was vaporized using an emanator configured to a liquid petroleum gas (LPG) canister, placed inside experimental huts (phase 1) or outdoors (phase 2), and evaluated for reductions in human landing rate, density, knockdown and mortality rates of An. funestus, which are present in high density in the area. To demonstrate the mosquito recruiting effect of LPG, a hut with only an LPG cooker but no metofluthrin was added as a comparator and compared with an LPG cooker burning alongside the emanator and a third hut with no LPG cooker as control. Phase 2 evaluated the protective range of the SR product while emanating from the centre of a team of mosquito collectors sitting outdoors in north, south, east and west directions at 5, 10 and 20 feet from the emanating device. RESULTS Combustion of LPG with a cook stove increased the density of An. funestus indoors by 51% over controls with no cook stove. In contrast, huts with metofluthrin vaporized with LPG combustion had lower indoor density of An. funestus (99.3% less than controls), with knockdown and mortality rates of 95.5 and 87.7%, respectively, in the mosquitoes collected in the treated huts. In the outdoor study (phase 2), the outdoor landing rate was significantly lower at 5 and 10 feet than at 20 feet from the emanator. CONCLUSIONS Vaporized metofluthrin almost completely prevented An. funestus landing indoors and led to 10 times lower landing rates within 10 feet of the emanator outdoors, the first product to demonstrate such potential. Cooking with LPG inside the house could increase exposure to Anopheles mosquito bites, but the use of the metofluthrin canister eliminates this risk.
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Affiliation(s)
- Silas Agumba
- Centre for Global Health Research, Kenya Medical Research Institute, P.O. Box 1578-40100, Kisumu, Kenya.
| | - Vincent Moshi
- Centre for Global Health Research, Kenya Medical Research Institute, P.O. Box 1578-40100, Kisumu, Kenya
| | - Margaret Muchoki
- Centre for Global Health Research, Kenya Medical Research Institute, P.O. Box 1578-40100, Kisumu, Kenya
| | - Seline Omondi
- Centre for Global Health Research, Kenya Medical Research Institute, P.O. Box 1578-40100, Kisumu, Kenya
| | - Jackline Kosgei
- Centre for Global Health Research, Kenya Medical Research Institute, P.O. Box 1578-40100, Kisumu, Kenya
| | - Edward D Walker
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, MI, 48824, USA
| | - Bernard Abong'o
- Centre for Global Health Research, Kenya Medical Research Institute, P.O. Box 1578-40100, Kisumu, Kenya
| | - Nicole Achee
- Department of Biological Sciences, Eck Institute for Global Health, University of Notre Dame, Notre Dame, IN, USA
| | - John Grieco
- Department of Biological Sciences, Eck Institute for Global Health, University of Notre Dame, Notre Dame, IN, USA
| | - Eric Ochomo
- Centre for Global Health Research, Kenya Medical Research Institute, P.O. Box 1578-40100, Kisumu, Kenya.
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Swai JK, Soto AC, Ntabaliba WS, Kibondo UA, Ngonyani HA, Mseka AP, Ortiz A, Chura MR, Mascari TM, Moore SJ. Efficacy of the spatial repellent product Mosquito Shield™ against wild pyrethroid-resistant Anopheles arabiensis in south-eastern Tanzania. Malar J 2023; 22:249. [PMID: 37649032 PMCID: PMC10466708 DOI: 10.1186/s12936-023-04674-4] [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: 01/30/2023] [Accepted: 08/13/2023] [Indexed: 09/01/2023] Open
Abstract
BACKGROUND Spatial repellents that create airborne concentrations of an active ingredient (AI) within a space offer a scalable solution to further reduce transmission of malaria, by disrupting mosquito behaviours in ways that ultimately lead to reduced human-vector contact. Passive emanator spatial repellents can protect multiple people within the treated space and can last for multiple weeks without the need for daily user touchpoints, making them less intrusive interventions. They may be particularly advantageous in certain use cases where implementation of core tools may be constrained, such as in humanitarian emergencies and among mobile at-risk populations. The purpose of this study was to assess the efficacy of Mosquito Shield™ deployed in experimental huts against wild, free-flying, pyrethroid-resistant Anopheles arabiensis mosquitoes in Tanzania over 1 month. METHODS The efficacy of Mosquito Shield™ transfluthrin spatial repellent in reducing mosquito lands and blood-feeding was evaluated using 24 huts: sixteen huts were allocated to Human Landing Catch (HLC) collections and eight huts to estimating blood-feeding. In both experiments, half of the huts received no intervention (control) while the remaining received the intervention randomly allocated to huts and remained fixed for the study duration. Outcomes measured were mosquito landings, blood-fed, resting and dead mosquitoes. Data were analysed by multilevel mixed effects regression with appropriate dispersion and link function accounting for volunteer, hut and day. RESULTS Landing inhibition was estimated to be 70% (57-78%) [IRR 0.30 (95% CI 0.22-0.43); p < 0.0001] and blood-feeding inhibition was estimated to be 69% (56-79%) [IRR 0.31 (95% CI 0.21-0.44; p < 0.0001] There was no difference in the protective efficacy estimates of landing and blood-feeding inhibition [IRR 0.98 (95% CI 0.53-1.82; p = 0.958]. CONCLUSIONS This study demonstrated that Mosquito Shield™ was efficacious against a wild pyrethroid-resistant strain of An. arabiensis mosquitoes in Tanzania for up to 1 month and could be used as a complementary or stand-alone tool where gaps in protection offered by core malaria vector control tools exist. HLC is a suitable technique for estimating bite reductions conferred by spatial repellents especially where direct blood-feeding measurements are not practical or are ethically limited.
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Affiliation(s)
- Johnson Kyeba Swai
- Vector Control Product Testing Unit, Environmental Health and Ecological Science Department, Ifakara Health Institute, Bagamoyo, Tanzania
- Department of Epidemiology and Public, Health Swiss Tropical and Public Health Institute, Allschwil, Switzerland
- University of Basel, Basel, Switzerland
| | - Alina Celest Soto
- Vector Control Product Testing Unit, Environmental Health and Ecological Science Department, Ifakara Health Institute, Bagamoyo, Tanzania
- Department of Epidemiology and Public, Health Swiss Tropical and Public Health Institute, Allschwil, Switzerland
| | - Watson Samuel Ntabaliba
- Vector Control Product Testing Unit, Environmental Health and Ecological Science Department, Ifakara Health Institute, Bagamoyo, Tanzania
| | - Ummi Abdul Kibondo
- Vector Control Product Testing Unit, Environmental Health and Ecological Science Department, Ifakara Health Institute, Bagamoyo, Tanzania
| | - Hassan Ahamad Ngonyani
- Vector Control Product Testing Unit, Environmental Health and Ecological Science Department, Ifakara Health Institute, Bagamoyo, Tanzania
| | - Antony Pius Mseka
- Vector Control Product Testing Unit, Environmental Health and Ecological Science Department, Ifakara Health Institute, Bagamoyo, Tanzania
| | | | | | | | - Sarah Jane Moore
- Vector Control Product Testing Unit, Environmental Health and Ecological Science Department, Ifakara Health Institute, Bagamoyo, Tanzania
- Department of Epidemiology and Public, Health Swiss Tropical and Public Health Institute, Allschwil, Switzerland
- University of Basel, Basel, Switzerland
- School of Life Sciences and Bio Engineering, The Nelson Mandela, African Institution of Science and Technology, Tengeru, Arusha, United Republic of Tanzania
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Achee NL, Perkins TA, Moore SM, Liu F, Sagara I, Van Hulle S, Ochomo EO, Gimnig JE, Tissera HA, Harvey SA, Monroe A, Morrison AC, Scott TW, Reiner RC, Grieco JP. Spatial repellents: The current roadmap to global recommendation of spatial repellents for public health use. CURRENT RESEARCH IN PARASITOLOGY & VECTOR-BORNE DISEASES 2022; 3:100107. [PMID: 36590345 PMCID: PMC9801085 DOI: 10.1016/j.crpvbd.2022.100107] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/26/2022] [Revised: 11/18/2022] [Accepted: 12/04/2022] [Indexed: 12/13/2022]
Abstract
Spatial repellent (SR) products are envisioned to complement existing vector control methods through the continual release of volatile active ingredients (AI) providing: (i) protection against day-time and early-evening biting; (ii) protection in enclosed/semi-enclosed and peri-domestic spaces; (iii) various formulations to fit context-specific applications; and (iv) increased coverage over traditional control methods. SR product AIs also have demonstrated effect against insecticide-resistant vectors linked to malaria and Aedes-borne virus (ABV) transmission. Over the past two decades, key stakeholders, including World Health Organization (WHO) representatives, have met to discuss the role of SRs in reducing arthropod-borne diseases based on existing evidence. A key focus has been to establish a critical development path for SRs, including scientific, regulatory and social parameters that would constitute an outline for a SR target product profile, i.e. optimum product characteristics. The principal gap is the lack of epidemiological data demonstrating SR public health impact across a range of different ecological and epidemiological settings, to inform a WHO policy recommendation. Here we describe in brief trials that are designed to fulfill evidence needs for WHO assessment and initial projections of SR cost-effectiveness against malaria and dengue.
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Affiliation(s)
- Nicole L. Achee
- Department of Biological Sciences, Eck Institute for Global Health, University of Notre Dame, Notre Dame, IN, USA,Corresponding author. Department of Biological Sciences, Eck Institute for Global Health, 239 Galvin Life Science Center, Notre Dame, IN, 46556, USA.
| | - T. Alex Perkins
- Department of Biological Sciences, Eck Institute for Global Health, University of Notre Dame, Notre Dame, IN, USA
| | - Sean M. Moore
- Department of Biological Sciences, Eck Institute for Global Health, University of Notre Dame, Notre Dame, IN, USA
| | - Fang Liu
- Department of Applied and Computational Mathematics and Statistics, University of Notre Dame, Notre Dame, IN, USA
| | - Issaka Sagara
- Malaria Research and Training Center (MRTC), Faculty of Medicine, Dentistry and Pharmacy at the University of Sciences, Techniques and Technologies of Bamako (USTTB), Bamako, Mali
| | | | - Eric O. Ochomo
- Kenya Medical Research Institute, Centre for Global Health Research, Kisumu, Kenya
| | - John E. Gimnig
- Centers for Disease Control and Prevention, Division of Parasitic Diseases and Malaria, Atlanta, GA, USA
| | | | - Steven A. Harvey
- Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, USA
| | - April Monroe
- Johns Hopkins Center for Communication Programs, Baltimore, MD, USA
| | - Amy C. Morrison
- Department of Pathology, Microbiology, and Immunology, School of Veterinary Medicine, University of California, Davis, CA, USA
| | - Thomas W. Scott
- Department of Entomology and Nematology, University of California, Davis, CA, USA
| | - Robert C. Reiner
- Department of Health Metrics Sciences, University of Washington, Seattle, WA, USA
| | - John P. Grieco
- Department of Biological Sciences, Eck Institute for Global Health, University of Notre Dame, Notre Dame, IN, USA
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