Project Summary
Bancroftian filariasis is prevalent in 27 out of 28 districts in Malawi. Elimination efforts of this debilitating disease have seen some areas receiving >5 rounds of mass drug administration (MDA) with Albendazole and Ivermectin. MDA campaigns should partly result in reduction infection rates and transmission.
This study aims at investigating the role of various mosquito genera in LF transmission and their response to public health insecticides. The study was implemented in 3 districts (Chikhwawa, Mchinji and Karonga) in Malawi.
Using pyrethrum space spray catches (PSCs) approximately 3,582 mosquitoes were collected between 2011 and 2012. Anopheles gambiae were the predominant species collected (78.9%; n = 2,825), followed by An. funestus (10.6%; n = 381) and Culexsp (9.5%; n = 341). Analysis of 1,000 Anopheles sp specimens revealed that 0.3% were harbouring W. bancrofti parasites, a significant drop from previously reported infection rates of 2-3%.
An. funestus showed high levels of resistance to the three pyrethroids tested; Permethrin, Deltamethrin and Lambdacyhalothrin (20% – 46% mortality rates) at one site but was completely susceptible to an organophosphate, Malathion (99% mortality). At the same site, An. gambiae was also susceptible to carbamates and organophosphate but showed resistance to DDT (73.1% mortality). Culexsp was resistant to all four classes of insecticides tested with mortality rates ranging from 0% (DDT) to 86.1% (Malathion).
The low W. bancrofti infection rates observed are encouraging. However, the high levels of resistance seen in all vector species is worrisome and deserve further monitoring and investigation to see the relation between transmission and resistance patterns.