Dr. Powell's main research interests are in the host-parasite relationships of coccidian parasites. In particular, he is studying the pathology, immunology and cell biology of Sarcocystis and porcine toxoplasmosis. These studies include the ultrastructural development of parasite induced pathogenesis, the cell mediated and humoral responses of the host to the presence of the parasites, the analysis of immunogenic surface polypeptides and genetically based differences in host responses to sarcocystosis.