Malaria parasites are usually regarded as vertebrate parasites that rely on a mosquito vector for transmission, such that most research has focused on vertebrate-parasite interactions. Unlike human or rodent malaria, avian malaria is commonly found in wild populations of its vertebrate host in North America, usually without obvious clinical signs in the birds. Bird-parasite interactions alone, however, do not satisfactorily explain some of the major findings that have emerged from recent molecular studies on avian malaria, such as the high genetic diversity and geographic localization of some parasite lineages. Coadaptation with mosquito hosts may result in the geographic localization of avian malaria parasites. We will test this hypothesis by controlled infections of different species and populations of bird-feeding mosquito species to compare their ability to transmit parasites using a parasite lineage that is restricted to the eastern U.S. If mosquito-parasite coadaptation is indeed important in this system, only eastern mosquitoes should harbor sporozoites.
These experiments will fill a gap in a rapidly growing body of knowledge concerning the ecology and evolution of malaria parasites by explicitly testing whether mosquito-parasite interactions can influence the geographic distribution of malaria parasite lineages. Results from this study could inform efforts to predict the effects of climate change on vector-borne disease distribution, and could support an ecological redefinition of malaria as a mosquito parasite that relies on vertebrates for dispersal.
