Date Published: March 22, 2018
Publisher: The American Society of Tropical Medicine and Hygiene
Author(s): Elizabeth Hemming-Schroeder, Stephanie Strahl, Eugene Yang, Amanda Nguyen, Eugenia Lo, Daibin Zhong, Harrysone Atieli, Andrew Githeko, Guiyun Yan.
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 (kdr) mutation frequencies for Anopheles arabiensis in Western Kenya heightens the concern on the future effectiveness of ITNs in Kenya. We examined resistance in An. arabiensis populations across Kenya through kdr mutations and World Health Organization–recommended bioassays. We detected two kdr alleles, L1014F and L1014S. Kdr mutations were found in five of the 11 study sites, with mutation frequencies ranging from 3% to 63%. In two Western Kenya populations, the kdr L1014F allele frequency was as high as 10%. The L1014S frequency was highest at Chulaimbo at 55%. Notably, the kdr L1014F mutation was found to be associated with pyrethroid resistance at Port Victoria, but kdr mutations were not significantly associated with resistance at Chulaimbo, which had the highest kdr mutation frequency among all sites. This study demonstrated the emerging pyrethroid resistance in An. arabiensis and that pyrethroid resistance may be related to kdr mutations. Resistance monitoring and management are urgently needed for this species in Kenya where resistance is emerging and its abundance is becoming predominant. Kdr mutations may serve as a biomarker for pyrethroid resistance in An. arabiensis.
Despite intensive malaria control efforts, malaria remains a leading cause of morbidity and mortality in Kenya, especially among younger children and pregnant women.1 Vector control programs, particularly in the form of insecticide-treated bed nets (ITNs) are essential for achieving malaria elimination goals2,3 and have coincided with a decrease in malaria-related morbidity rates in Kenya.4 However, increasing insecticide resistance threatens the efficacy of antimalarial interventions.5
The observed high proportions of An. arabiensis in this study demonstrate the ongoing species composition shift from predominantly An. gambiae s.s. to An. arabiensis in East Africa.2,24–27 A decline in An. gambiae s.s. relative abundance yet stable population of An. arabiensis has been observed in the lowlands of Kenya in conjunction with an increase in ITN coverage.2,7,23,27 These findings underscore the importance of the role that An. arabiensis are playing in maintaining residual malaria transmission, and as such, will present a major barrier to malaria control and elimination. Understanding An. arabiensis insecticide resistance mechanisms and monitoring for resistance are essential for achieving malaria elimination goals.