N. Lissenden1, T. Churcher2, P. Hancock3, H. M. Ismail1, M. Kont2, B. Lambert2, A. Lenhart4, P. J. McCall1, C. Moyes3, M. J. Paine1, G. Praulins1, D. Weetman1 & R. S. Lees1
1 Liverpool School of Tropical Medicine, UK . 2 Imperial Collage London, UK . 3 University of Oxford, UK . 4 Integrated Vector Management Team, Centres for Disease Control, US
Pyrethroid resistance is widespread in malaria vectors. However, differential mortality in discriminating dose assays to different pyrethroids is often observed in the field. When this occurs, it is unclear if this differential mortality should be interpreted as an indication of differential levels of susceptibility within the pyrethroid class. And if so, should countries consider preferentially selecting a specific pyrethroid for programmatic use over another.
Researchers from the Liverpool School of Tropical Medicine, University of Oxford, Imperial Collage London, and US Centres for Disease Control, reviewed evidence from molecular studies, insecticide resistance patterns and testing results (from laboratory colonies and field data), and behavioural assays to answer these questions, responding to a call from The Global Fund to Fight AIDS, Tuberculosis and Malaria.
Where one pyrethroid is seen to be consistently more effective in resistance screening, preferably coupled with additional, more direct evidence, the pyrethroid with the greater killing capacity should probably be deployed, if costs and other considerations, most notably formulation or delivery method (e.g. net type), are comparable. However, the evidence suggests that in areas where pyrethroid resistance exists, different results in insecticide susceptibility assays are not necessarily indicative of a true or operationally relevant difference in potential performance of the specific pyrethroids currently in common use (deltamethrin, permethrin, α-cypermethrin and λ-cyhalothrin). It is not advisable to use rotation between these pyrethroids as an insecticide resistance management strategy.
See also: Moyes CL, Lees RS, Yunta C, Walker KJ, Hemmings K, Oladepo F, Hancock PA, Weetman D, Paine MJI, Ismail HM, 2021. Assessing cross-resistance within the pyrethroids in terms of their interactions with key cytochrome P450 enzymes and resistance in malaria vector populations. Parasite and Vector (In press).