Effects of long-lasting insecticidal nets and zooprophylaxis on mosquito feeding behaviour and density in Mwea, central Kenya

Abstract

Background & objectives: Zooprophylaxis is a strategy that can control malaria by attracting mosquitoes to domestic animals that act as dead-end hosts. The objective of this study was to establish the effects of zooprophylaxis and long-lasting insecticidal nets (LLINs) on malaria transmission in an agro-based ecosystem with seasonal transmission. Methods: The mosquito samples were collected indoors using the space spray catch method before and after intervention between October 2005 and March 2006 to determine the mosquito densities and the feeding patterns of Anopheles spp in Mwea, Kenya. Results: A total of 4148 mosquito samples were collected, out of which 11 (0.2%) were tested positive for sporozoites. Ten were Anopheles gambiae species and one was An. funestus species. Results on blood meal ELISA showed that in the household categories that used bednets and kept one cow there was a decrease in relative change ratio (post-/pre-intervention) of 87.5 and 19.6% (p <0.05) in human and cattle blood intake respectively. For households that kept 2–4 cattle and used bednets, there was a decrease in cattle blood index (CBI) by 61.9% and an increase in human blood index (HBI) by 2%, which was not significant (p >0.05). In households with >4 cattle and bednet, there was significant reduction (p <0.05) in CBI of 37.5% as compared to the reduction of 10.3% in HBI. The ratios of man biting rates (MBR) decreased significantly, as you move up from households with one cattle with or without LLINs to households with more than four cattle with or without LLINs with a regression coefficient of –0.96; SE = 0.834; p = 0.017. Similarly, the HBI decreased significantly with the regression coefficient of 0.239; SE = 0.039; p = 0.015 (p <0.05) especially in households with >4 cattle. Interpretation & conclusion: This study demonstrated that there were additive effects of zooprophylaxis and LLINs in the control of mosquito density and reduction of human risk to the mosquito bites. However, in Integrated Vector Management (IVM), the number of animals per household should not be more than four.