Evaluation of polythylene based long lasting treated bed nets on the population density of indoor resting anopheles mosquitoes in Kanyaboli, Western-Kenya

Abstract

Insecticide treated bednets have been shown to have a profound impact on malaria transmission in experimental trials in sub-saharan Africa. Their effectiveness requires frequent re-treatment, however re-treatment rates have rarely risen above 20%. The need for re-impregnation and the relatively short life span led to the development of long lasting insecticide bed nets (LLINs) for longer field use. Though these LLINs have shown good efficacy on malaria mosquitoes under control conditions, no fields study have been done of these LLIN for longer term field use. This study was therefore undertaken to evaluate the impact of deltamethrine treated bednets Netprotect, on density indoor resting of Anopheles mosquitoes in Western Kenya. In addition the study also investigated the impact of Netprotect on the feeding success of Anopheles mosquitoes' on human blood. These LLINs Netprotect bednets were randomly distributed in 150 matched houses. Another 150 houses were selected 2kms away as the control. These households recieved their bedntes six months later. Indoor resting mosquitoes from both areas were collected using Pyrethrum Spray Catch (PSC) and then sorted according to their psychological status namely, unfed, fed, and gravid. Blood meals were identified by a direct Enzyme linked immunosorbent assay (ELISA) using anti-host (IgG) conjugate. Malaria cases from both areas were followed passively in the nearby clinic by clinical diagnosis and rapid diagnosis test kit (Paracheque). Net efficacy was tested by exposing mosquitoes for 3 min using standard WHO test cones on selected net samples. Comparison of proportions between categorical variables was performed by chi-square test at 95% confidence level using SAS statistical software version 9. The findings revealed that the probability of finding An. funestus in control area was twice times more likely than in intervention area (OR=2.4,CI 1.7:3.5). There were decreased human feeding and increased cattle feeding by An. funestus in the intervention area. An arabiensis from this area was found to be highly zoophilic. Biossay on residual insecticidal activity indicated that Netprotect bed nets killed 80% of the exposed laboratory colony of susceptable An. gambiae s.s (Kisumu strain) after one year of use. The malaria cases followed for seven months at Ratuoro health center showed a reduced prevalence in the intervention area. These results indicated that Netprotect bednets were effective in controlling Anopheles mosquitoes during one year of use and this enhanced their ability to reduce malaria prevalence in the intervention area.