My laboratory studies population genetics of Toxoplasma gondii. Toxoplasma is an apicomplexan parasite related to the causative agents of malaria (Plasmodium spp) and coccidiosis (Eimeria spp). It parasitizes most vertebrates including mammals and birds. In some geographic regions up to 80% of the human population is chronically infected. Toxoplasma has emerged as a major opportunistic pathogen in immunocompromised patients (AIDS, cancer chemotherapy and organ transplant). It also causes congenital defects in humans. Through international collaboration, we have studied over 1400 T. gondii isolates and identified 200 unique genotypes worldwide. Preliminary analysis of the data indicates subpopulation structures in different continents, as well as worldwide distribution of a few clonal lineages. We are currently sequencing multiple loci (~50) for each of these unique genotypes. This study will determine the genetic diversity, population structure, the intensity of genetic recombination and selection of the genome, providing information on the evolution of T. gondii. The results will provide us information regarding epidemiology and transmission of the parasite in animal and human populations, which will help develop intervention strategy to prevent the spread of T. gondii.