| Although the definition of "highland" is subjective, the prevalence of Plasmodium falciparum is found generally to decrease with increasing altitude. The relatively low incidence of disease may result in diminished human immunity, so epidemics in the highlands often cause severe morbidity and mortality. In the western Kenyan highlands, malaria incidence apparently has been increasing over the past few decades, but explanations for such patterns remain incomplete. The specific ecological requirements of anopheline mosquito vectors and the Plasmodium parasites they transmit suggest the importance of the environmental context of risk. Although topographic trends may generally determine risk for disease, the way in which humans interact with the environmental context in which they live likely can modify that risk.;This dissertation investigates the confluence of environmental, topographic, and human determinants of household malaria in two highland communities of western Kenya. Household case data from 2001-2004 were analyzed for demographic and environmental risk factors using clinically-derived case information, high-resolution satellite imagery, and digital elevation models to explore how local topography, land-cover, and land-use influence infection risk. Results demonstrated that malaria risk in this region is largely determined by strong, topographically-determined contextual determinants of risk, such as the proximity of houses to remotely sensed swamplands or, analogously but more specifically, to regions of the landscape where water can be predicted to collect on the basis of hydrologic models. Household malaria was also found to be related to human variables related to agriculture, deforestation, and urban density. These results confirm the importance of considering the environmental context in which malaria transmission occurs. |
