Emerging Pyrethroid Resistance among Anopheles arabiensis in Kenya

Abstract

Vector control programs, particularly in the form of insecticide-treated bed nets (ITNs), are essential for achieving malaria elimination goals. Recent reports of increasing knockdown resistance (<i>kdr</i>) mutation frequencies for <i>Anopheles arabiensis</i> in Western Kenya heightens the concern on the future effectiveness of ITNs in Kenya. We examined resistance in <i>An. arabiensis</i> populations across Kenya through <i>kdr</i> mutations and World Health Organization-recommended bioassays. We detected two <i>kdr</i> alleles, L1014F and L1014S. <i>Kdr</i> mutations were found in five of the 11 study sites, with mutation frequencies ranging from 3% to 63%. In two Western Kenya populations, the <i>kdr</i> L1014F allele frequency was as high as 10%. The L1014S frequency was highest at Chulaimbo at 55%. Notably, the <i>kdr</i> L1014F mutation was found to be associated with pyrethroid resistance at Port Victoria, but <i>kdr</i> mutations were not significantly associated with resistance at Chulaimbo, which had the highest <i>kdr</i> mutation frequency among all sites. This study demonstrated the emerging pyrethroid resistance in <i>An. arabiensis</i> and that pyrethroid resistance may be related to <i>kdr</i> mutations. Resistance monitoring and management are urgently needed for this species in Kenya where resistance is emerging and its abundance is becoming predominant. <i>Kdr</i> mutations may serve as a biomarker for pyrethroid resistance in <i>An. arabiensis</i>.