Blood meal origins and insecticide susceptibility of Anopheles arabiensis from Chano in South-West Ethiopia

Abstract

BackgroundAnopheles arabiensis, the main malaria vector in Ethiopia, shows both anthropophilic and zoophilic behaviours. Insecticide resistance is increasing, and alternative methods of vector control are needed. The objectives of this study were to determine the blood meal origins and the susceptibility to insecticides of An. arabiensis from Chano village near Arba Minch in South-West Ethiopia.MethodsBlood meal sources of anopheline mosquitoes collected using Centers for Disease Control and Prevention (CDC) light traps and pyrethrum spray catches (PSC) from human dwellings, and hand-held mouth aspirators from outdoor pit shelters were analysed using a direct enzyme-linked-immunosorbent assay (ELISA). The susceptibility of An. arabiensis to pyrethroid insecticides (alphacypermethrin, lambdacyhalothrin, deltamethrin, and cyfluthrin) and DDT was assessed using females reared from larval and pupal collections from natural breeding sites.ResultsThe blood meal origins of 2967 freshly fed Anopheles mosquitoes were determined. An. arabiensis was the predominant species (75%), and it fed mainly on cattle. The densities of both freshly fed An. arabiensis and those fed on human blood followed similar seasonal patterns. The overall human blood index (HBI) of An. arabiensis, including mixed blood meals, was 44% and the bovine blood index (BBI) was 69%. The HBI of An. arabiensis from CDC light trap collections was 75% and this was higher than those for PSC (38%) and outdoor pit shelter collections (13%), while the BBI was 65% for PSC, 68% for outdoor pit shelters and 72% for CDC light traps. More freshly fed and human blood-fed An. arabiensis were sampled from houses close to the shore of Lake Abaya (the major breeding site).A high proportion of An. arabiensis was resistant to the pyrethroid insecticides, with a mortality rate of 56% for lambdacyhalothrin, 50% for cyfluthrin and alphacypermethrin, 47% for deltamethrin, and 10% for DDT.ConclusionAnopheles arabiensis is the predominant species of anopheline mosquito in this region, and cattle are the main source of its blood meals. The greater tendency of this species to feed on cattle justifies the application of insecticides on cattle to control it. However, An. arabiensis has already developed resistance to the available pyrethroid insecticides, and alternative insecticides are needed for malaria vector control.

Comparative entomological study on ecology and behaviour of Anopheles mosquitoes in highland and lowland localities of Derashe District, southern Ethiopia

“…arabiensis showed zoophilic and an exophilic tendency, which is in harmony with what was documented before [21]. The preference of An.arabiensis to feed on cattle and rest outside after feeding in this study strengthens the findings of the study in Chalo of Southern Ethiopia, 65 km away from the current study area [31]. The experimental study in Tanzania also confirmed its tendency to escape from houses after feeding [32].…”

Exploring the potential of using cattle for malaria vector surveillance and control: a pilot study in western Kenya

“…Furthermore, the insecticide tested is identical to those used for mosquito control indoors and subject to increasing levels of resistance [45]. Accordingly, treating cattle for mosquito control with pyrethroids is unlikely to be sustainable and frequent application would contribute to even more rapid development of resistance [46]. Already, deltamethrin resistance of An.…”

“…Research into long-lasting formulations persisting at least for 1 month would be desirable. However, given that pyrethroids are the only class of insecticide currently licensed to treat mosquito nets, and the increasing resistance of malaria vectors against pyrethroids insecticides [45], it would be wise to investigate alternatives with a completely different mode of action [9, 46]. Our entomological sampling with CBTs highlights that targeting cattle for mosquito control has potential.…”

Entomologic Inoculation Rates of Anopheles arabiensis in Southwestern Ethiopia

“…Anopheles arabiensis has developed resistance to the pyrethroid insecticides and DDT, and showed a greater tendency to feed on cattle than humans, with an overall human blood index (HBI; the proportion of the An. arabiensis fed on human blood meals of the total blood meals determined) of 44% and a bovine blood index of 69% 18. We report anopheline species diversity, monthly variations of An.…”