Influence of host and larval habitat distribution on the abundance of African malaria vectors in western Kenya

The abundance of anopheline mosquitoes varies substantially among houses within the same villages. Anopheles gambiae sensu stricto is highly anthropophilic, and Anopheles arabiensis is zoophilic; thus, it is often hypothesized that the abundance of An. gambiae and An. arabiensis in a house is associated with the distribution of livestock and humans. In this paper we examined the influence of livestock and human host availability on the distribution and abundance of malaria vectors in the basin region of Lake Victoria in western Kenya. Larvae and adults of An. gambiae, An. arabiensis and Anopheles funestus were collected in the beginning and the end of the rainy season in 1999. Anopheles gambiae was the predominant species in both larval and adult samples. Multiple regression analyses found that the ratio of distance between houses and larval habitats to distance between cowsheds and larval habitats had a significant and negative association with the relative abundance of An. gambiae larvae for both sampling periods. The ratio of human density to cow density was positively correlated with the relative abundance of An. gambiae larvae in the late rainy period. For the adult samples, distance from a house to its nearest larval habitats was the only variable that showed a significant correlation with the An. gambiae density in houses in both sample periods. More than 90% of anopheline adults were found in the houses within 300 meters from the nearest larval habitats. Anopheline mosquito density was not correlated to the density of cows or humans, or the distance to cowsheds from houses. These results suggest that livestock and human host availability affect the relative abundance of An. gambiae larvae in aquatic habitats, but the distribution of anopheline adults in houses is determined by the distance from houses to larval habitats.