Determination of the discriminating concentration of chlorfenapyr (pyrrole) and Anopheles gambiae sensu lato susceptibility testing in preparation for distribution of Interceptor® G2 insecticide-treated nets

• Published in: Malaria Journal
• Main Authors: Richard M. Oxborough, Aklilu Seyoum, Yemane Yihdego, Joseph Chabi, Francis Wat’senga, Fiacre R. Agossa, Sylvester Coleman, Samdi Lazarus Musa, Ousmane Faye, Michael Okia, Mohamed Bayoh, Evelyne Alyko, Jean-Desire Rakotoson, Hieronymo Masendu, Arthur Sovi, Libasse Gadiaga, Bernard Abong’o, Kevin Opondo, Ibrahima Baber, Roch Dabire, Virgile Gnanguenon, Gedeon Yohannes, Kenyssony Varela, Etienne Fondjo, Jenny Carlson, Jennifer S. Armistead, Dereje Dengela
• Format: Article in Journal/Newspaper
• Language: English
• Published: BMC 2021
• Subjects: Chlorfenapyr; Pyrrole; Anopheles gambiae; Interceptor G2; CDC bottle bioassay; Discriminating concentration; Arctic medicine. Tropical medicine; RC955-962; Infectious and parasitic diseases; RC109-216; Arctic
• Online Access: https://doi.org/10.1186/s12936-021-03847-3; https://doaj.org/article/178891234e0b44b0a55d29c0a9e364d6

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 ...