Spatial distribution and habitat characterisation of anopheles mosquito adults and larvae in Nyabushozi County, Kiruhura District.

Abstract

Surveys were conducted to characterize the habitats of the larvae and adults of Anopheles mosquitoes and determine their spatial distribution in Nyabushozi county, Kiruhura district, in south western Uganda. A total of 74 households were randomly selected for the study out of a total of 588 in 8 villages. These households represented the three categories of targeted communities (pastoralists, transitional and settled) and were geo-referenced using Geographical Positioning System (GPS). The abundance of anopheline mosquitoes varied substantially among houses within the same villages. Larvae and adults of An. Gambiae, and Anopheles funestus were collected in the beginning and the end of three rainy seasons. Chi square analysis revealed that the relationship of distance between breeding houses and larval habitats had a significant and positive association with the relative abundance of An. Gambiae and An. Funestus larvae for both sampling periods. For the adult samples, distance from a house to it’s nearest larvae habitats was the only variable that showed a significant correlation with An. Gambiae and An. Funestus density in houses sampled in both sample periods. More than 90% of anopheline adults were found in houses within 400 meters from the nearest larvae habitat. The breeding of mosquitoes and larvae assemblage was influenced by physical factors in habitats such as temperature, light (canopy coverage), ion concentration (pH), substrate, turbidity and floating vegetation. Significantly higher densities of Anopheles larvae were collected in breeding sites that were turbid and shallow, with no or slow movement of water. The highest larval density was recorded in hoof prints that had pH readings of 5-5.5. The density of larvae was significantly affected by the presence of floating vegetation in valley dams and shade around them. There was a significant relationship between malaria incidence, house type and distance to a breeding habitat. The risk of getting malaria was greater for inhabitants of poor type of house construction (incomplete, mud, or grass thatched wall, grass roof) compared to houses within complete brick and plaster walls and roofed with iron sheet.