Malaria parasite dispersal patterns are complex, as they are affected by both the movement of mosquitoes and humans. Mosquito dispersal distance ranges from less than one to several kilometers throughout a lifetime, whereas humans can carry malaria parasites over immense distances. Previous population genetic studies suggest that the highlands surrounding the Rift Valley are barriers to mosquito gene flow (dispersal) across Kenya. However, the arid landscape and sparse human densities between Western and Eastern Kenya may also restrict gene flow. Here, we disentangle the effects of elevation, land cover type, and human population density on gene flow of malaria parasites and mosquitoes across Kenya using a landscape genetics approach. Landscape genetics uses techniques in population genetics, landscape ecology, and spatial statistics to quantify the effects of landscape factors on genetic differentiation. We genotyped the malaria parasite Plasmodium falciparum and major malaria mosquito vectors Anopheles arabiensis and An. gambiae specimens collected from 14 study sites across Kenya at 9 microsatellite loci. Resistance costs in candidate resistance surfaces were optimized and pairwise landscape resistance distances were measured based on circuit theory. To determine the ecological variables most closely associated with gene flow, we fit linear mixed effects models with maximum-likelihood population effects.
Results/Conclusions
Preliminary analyses indicate that forest is a significant barrier to gene flow for An. arabiensis, while for An. gambiae, low precipitation is a significant barrier in Western Kenya. Analyses for P. falciparum will be similarly conducted as well as analyses at varying spatial scales. As areas approach malaria elimination, it is critical to understand the underlying factors that influence the dispersal of malaria parasites and vectors in order to effectively sustain local control and elimination. Moreover, knowledge of how malaria parasites and vectors disperse is also important to predicting how insecticide and antimalarial resistance spread. By identifying areas susceptible to malaria and mosquito vector spread, targeted public health interventions can be designed and implemented.