Richard M Oxborough1, Aklilu Seyoum2, Yemane Yihdego2, Joseph Chabi2, Francis Wat'senga3, Fiacre R Agossa4, Sylvester Coleman5, Samdi Lazarus Musa6, Ousmane Faye7, Michael Okia8, Mohamed Bayoh9, Evelyne Alyko9,10, Jean-Desire Rakotoson11, Hieronymo Masendu12, Arthur Sovi13,14,15, Libasse Gadiaga13, Bernard Abong'o16, Kevin Opondo16, Ibrahima Baber17, Roch Dabire18, Virgile Gnanguenon19, Gedeon Yohannes20, Kenyssony Varela21, Etienne Fondjo22, Jenny Carlson23, Jennifer S Armistead23, Dereje Dengela2. 1. PMI VectorLink Project, Abt Associates, 6130 Executive Blvd, Rockville, MD, 20852, USA. Richard_Oxborough@abtassoc.com. 2. PMI VectorLink Project, Abt Associates, 6130 Executive Blvd, Rockville, MD, 20852, USA. 3. Entomology Department, National Institute of Biomedical Research, Avenue de la Démocratie, Kinshasa, Democratic Republic of the Congo. 4. PMI VectorLink Project, Abt Associates, Kinshasa, Democratic Republic of the Congo. 5. PMI VectorLink Project, Abt Associates, Plot 11 Waterson Road, Fuo, Tamale, Ghana. 6. PMI VectorLink Project, Abt Associates, Gte No. 12 TOS Benson Crescent, Utako, Abuja, Nigeria. 7. Département de Biologie Animale, Université Cheikh Anta Diop, Bp 5005 Dakar-Fann, Dakar, Senegal. 8. PMI VectorLink Project, Abt Associates, Tororo, Uganda. 9. PMI VectorLink Project, Abt Associates, Njoka Road, Off Kwacha Road, Olympia, Box 39090, Lusaka, Zambia. 10. PMI VectorLink Project, Abt Associates, Freetown, Sierra Leone. 11. PMI VectorLink Project, Abt Associates, Lot Ex La Sice, Ambalanaomby, Farafangana, Madagascar. 12. PMI VectorLink Project, Abt Associates, 1 Pascoe Avenue, Belgravia, Harare, Zimbabwe. 13. PMI VectorLink Project, Abt Associates, Cite du Niger 1, Rue 30, Porte 612, Bamako, Mali. 14. Faculty of Infectious and Tropical Diseases, Disease Control Department, London School of Hygiene and Tropical Medicine, London, WC1E 7HT, UK. 15. Faculty of Agronomy, University of Parakou, BP 123, Parakou, Benin. 16. PMI VectorLink Project, Abt Associates, Whitehouse, Milimani, Kisumu, Ojijo Oteko Road, P.O. Box 895-40123, Kisumu, Milimani, Kenya. 17. PMI VectorLink Project, Abt Associates, 16th Street, Beach Side, Sinkor, Monrovia, Liberia. 18. Institute of Health Science Research, Malaria and Tropical Neglected Research Unit, 01 BP 545, Bobo-Dioulasso, Burkina Faso. 19. PMI VectorLink Project, Abt Associates, Plot 28 Avenue Pierre Ngendandumwe, Bujumbura, Burundi. 20. PMI VectorLink Project, Abt Associates, Gerje Rood Sami Building, Floor 1, Office no 105, P.O. Box : 13646, Addis Ababa, Ethiopia. 21. PMI VectorLink Project, Abt Associates, Rua Justino Chemane, No. 237 Sommerschield 2, Maputo, Mozambique. 22. PMI VectorLink Project, Abt Associates, P.O. Box 14 025, Mballa II, Dragages, P.O. Box 14 025, Yaounde, Cameroon. 23. U.S. President's Malaria Initiative, U.S. Agency for International Development, Washington, DC, USA.
Abstract
BACKGROUND: Following agricultural use and large-scale distribution of insecticide-treated nets (ITNs), malaria vector resistance to pyrethroids is widespread in sub-Saharan Africa. Interceptor® G2 is a new dual active ingredient (AI) ITN treated with alpha-cypermethrin and chlorfenapyr for the control of pyrethroid-resistant malaria vectors. In anticipation of these new nets being more widely distributed, testing was conducted to develop a chlorfenapyr susceptibility bioassay protocol and gather susceptibility information. METHODS: Bottle bioassay tests were conducted using five concentrations of chlorfenapyr at 12.5, 25, 50, 100, and 200 µg AI/bottle in 10 countries in sub-Saharan Africa using 13,639 wild-collected Anopheles gambiae sensu lato (s.l.) (56 vector populations per dose) and 4,494 pyrethroid-susceptible insectary mosquitoes from 8 colonized strains. In parallel, susceptibility tests were conducted using a provisional discriminating concentration of 100 µg AI/bottle in 16 countries using 23,422 wild-collected, pyrethroid-resistant An. gambiae s.l. (259 vector populations). Exposure time was 60 min, with mortality recorded at 24, 48 and 72 h after exposure. RESULTS: Median mortality rates (up to 72 h after exposure) of insectary colony mosquitoes was 100% at all five concentrations tested, but the lowest dose to kill all mosquitoes tested was 50 µg AI/bottle. The median 72-h mortality of wild An. gambiae s.l. in 10 countries was 71.5, 90.5, 96.5, 100, and 100% at concentrations of 12.5, 25, 50, 100, and 200 µg AI/bottle, respectively. Log-probit analysis of the five concentrations tested determined that the LC95 of wild An. gambiae s.l. was 67.9 µg AI/bottle (95% CI: 48.8-119.5). The discriminating concentration of 203.8 µg AI/bottle (95% CI: 146-359) was calculated by multiplying the LC95 by three. However, the difference in mortality between 100 and 200 µg AI/bottle was minimal and large-scale testing using 100 µg AI/bottle with wild An. gambiae s.l. in 16 countries showed that this concentration was generally suitable, with a median mortality rate of 100% at 72 h. CONCLUSIONS: This study determined that 100 or 200 µg AI/bottle chlorfenapyr in bottle bioassays are suitable discriminating concentrations for monitoring susceptibility of wild An. gambiae s.l., using mortality recorded up to 72 h. Testing in 16 countries in sub-Saharan Africa demonstrated vector susceptibility to chlorfenapyr, including mosquitoes with multiple resistance mechanisms to pyrethroids.
BACKGROUND: Following agricultural use and large-scale distribution of insecticide-treated nets (ITNs), malaria vector resistance to pyrethroids is widespread in sub-Saharan Africa. Interceptor® G2 is a new dual active ingredient (AI) ITN treated with alpha-cypermethrin and chlorfenapyr for the control of pyrethroid-resistant malaria vectors. In anticipation of these new nets being more widely distributed, testing was conducted to develop a chlorfenapyr susceptibility bioassay protocol and gather susceptibility information. METHODS: Bottle bioassay tests were conducted using five concentrations of chlorfenapyr at 12.5, 25, 50, 100, and 200 µg AI/bottle in 10 countries in sub-Saharan Africa using 13,639 wild-collected Anopheles gambiae sensu lato (s.l.) (56 vector populations per dose) and 4,494 pyrethroid-susceptible insectary mosquitoes from 8 colonized strains. In parallel, susceptibility tests were conducted using a provisional discriminating concentration of 100 µg AI/bottle in 16 countries using 23,422 wild-collected, pyrethroid-resistant An. gambiae s.l. (259 vector populations). Exposure time was 60 min, with mortality recorded at 24, 48 and 72 h after exposure. RESULTS: Median mortality rates (up to 72 h after exposure) of insectary colony mosquitoes was 100% at all five concentrations tested, but the lowest dose to kill all mosquitoes tested was 50 µg AI/bottle. The median 72-h mortality of wild An. gambiae s.l. in 10 countries was 71.5, 90.5, 96.5, 100, and 100% at concentrations of 12.5, 25, 50, 100, and 200 µg AI/bottle, respectively. Log-probit analysis of the five concentrations tested determined that the LC95 of wild An. gambiae s.l. was 67.9 µg AI/bottle (95% CI: 48.8-119.5). The discriminating concentration of 203.8 µg AI/bottle (95% CI: 146-359) was calculated by multiplying the LC95 by three. However, the difference in mortality between 100 and 200 µg AI/bottle was minimal and large-scale testing using 100 µg AI/bottle with wild An. gambiae s.l. in 16 countries showed that this concentration was generally suitable, with a median mortality rate of 100% at 72 h. CONCLUSIONS: This study determined that 100 or 200 µg AI/bottle chlorfenapyr in bottle bioassays are suitable discriminating concentrations for monitoring susceptibility of wild An. gambiae s.l., using mortality recorded up to 72 h. Testing in 16 countries in sub-Saharan Africa demonstrated vector susceptibility to chlorfenapyr, including mosquitoes with multiple resistance mechanisms to pyrethroids.
Authors: Rosemary Lees; Giorgio Praulins; Rachel Davies; Faye Brown; George Parsons; Anthony White; Hilary Ranson; Graham Small; David Malone Journal: Gates Open Res Date: 2019-07-10
Authors: Magellan Tchouakui; Tatiane Assatse; Leon M J Mugenzi; Benjamin D Menze; Daniel Nguiffo-Nguete; Williams Tchapga; Jonathan Kayondo; Francis Watsenga; Emile Zola Manzambi; Michael Osae; Charles S Wondji Journal: Infect Dis Poverty Date: 2022-04-25 Impact factor: 10.485