Increased globalization of the human economy, continued fragmentation of natural habitats, and widespread change in climate create conditions for the emergence of new diseases. Evaluating the potential for pathogens to switch between hosts requires, as a first step, an understanding of the diversity, distribution, and evolutionary history of disease organisms in nature. Mechanisms of species formation and host switching are basic to the emergence of new disease threats. This project uses avian malaria pathogens (Plasmodium and Haemoproteus) as a model system for studying evolutionary and ecological relationships between parasites and their hosts. Although malaria is common in birds, surprisingly little is known about the variety and distribution of these pathogens in nature. The disease can be detected readily in a blood sample when the host is infective. Because malaria is a devastating human disease, malaria parasites have been studied intensively, making possible the application of molecular techniques to recognize infections and DNA sequencing to identify evolutionary lineages. This technology will be used with samples from 22 localities in the Western Hemisphere, including the West Indies, to evaluate effects on the number of parasite lineages of host species richness and endemism, barriers to dispersal, and island size. The data obtained in this project also will be used to elucidate patterns of species formation, extirpation of populations, and extinction of lineages in avian malaria parasites. The history and geography of avian malaria parasites reflect spread and host switching in the past, which will provide insights into the general process of disease emergence.
