Malaria Transmission And Vector Ecology In A Reforested Swampy River Valley In Mbale, Vihiga District Of Western Kenya.
The ecology of malaria vectors and malaria transmission in a reforested swampy river valley in a western Kenya highland site were investigated, and the findings compared to those of a deforested site within the region. Data was collected from January 2005 to June 2005. Larval sampling was done to determine the relative abundance of anopheline larvae in habitats in the reforested area. Sampling of indoor resting Anopheles mosquitoes was done by Pyrethrum Spray Catch method (PSC), and the relative abundance/densities determined. Parasitological surveys were done to determine malaria parasite prevalence in school children within the sites. Survivorship of anopheline larvae in artificial habitats was investigated together with characteristics of natural habitats to determine the factors for the low survivorship of Anopheles larvae observed in the reforested site. More anopheline larvae were collected in habitats in the open sunlit patches than in the habitats under forest cover (X2=24.3524, df=l, P<O.OOOl) and canopy cover was negatively associated with larval abundance (P=0.0152). ~l!~]elative density of adult anopheline mosquitoes was significantly lower (F=39.l6, df=l,...5 P<O.OOOl) in the reforested site compared to the density of the same in the deforested area. The prevalence of P. falciparum parasites in school children at the reforested site was found to be significantly lower (X2=5.6, df=l, P=0.01796) than that of the deforested site. The overall mean larval survival time was shorter in the open sunlit habitats compared to that of the habitats under forest cover. (X2=110.5, df=l, P<O.OOOl)and X2=10.02, df=l, P=O. 0015 February 2005 and May 2005, respectively). On average it took a shorter time period (17 days) for larvae to develop into female adult stage in the habitats exposed to sunlight and a much longer time (27 days) in habitats under forest cover. Mean pupation rate was higher in open sunlit habitats than in forest habitats especially in the experiment done in May 2005. This study demonstrated a significant reduction in the survivorship of An. gambiae and An. Junestus larvae in the reforested larval habitats and hence a low abundance of the same. The adult vector mosquito population in the reforested site was far much less than the vector population in the deforested site; the same was also true for Plasmodium Jalciparum prevalence. The results of the study therefore, suggest that reforestation of the swampy river valleys may reduce survivorship of An gambiae and An Junestus larvae, which may lead to a low abundance of vector mosquitoes. Low abundance of vectors may result to a reduction in the entomological inoculation rate which may be one of the potential factors that may reduce malaria transmission in this area .