Some mosquitoes already have resistance to the latest weapon against malaria
(Science) An insecticide about to be widely deployed inside African homes to combat malaria-carrying mosquitoes is already losing its punch. Two years ago, the World Health Organization (WHO) gave the green light for clothianidin, long used in agriculture to kill crop pests, to be added to the current mainstays of indoor mosquito control, which are losing their effectiveness as the insects develop resistance. Since then, many African countries have been laying plans to spray the walls of homes with the pesticide—it would represent the first new class of chemicals adopted for such use in decades—and looking anxiously for evidence of pre-existing resistance.
Now, scientists at Cameroon’s Centre for Research in Infectious Diseases (CRID) have found it. They recently sampled mosquitoes from rural and urban areas around Yaoundé, the capital, including two key malaria carriers. In one standard susceptibility assay, exposure to clothianidin for 1 hour killed 100% of Anopheles coluzzii. But in some A. gambiae samples as many as 55% of the mosquitoes survived, the group reported in a preprint posted 7 August on the bioRxiv preprint server.
Corine Ngufor, a medical entomologist at the London School of Hygiene & Tropical Medicine, says this appears to be the first report of clear resistance to clothianidin in malaria-carrying insects. “It may spread very quickly and make this new class of insecticide almost useless for malaria vector control within a few years,” she warns.
Colince Kamdem, the CRID research scientist who led the study, says agricultural use of neonicotinoids—the class of chemicals to which clothianidin belongs—likely drove the emergence of the resistant mosquito strains.