While there has been significant research conducted about how bacteria and viruses cause disease, in comparison, relatively little is known about eukaryotic pathogenic processes – specifically, the disease-causing mechanisms of parasitic protozoans, which are single-celled, nucleated organisms. Dr. Michael Grigg is investigating the protozoan parasite Toxoplasma gondii, a common eukaryotic pathogen capable of infecting essentially any nucleated cell in most warm-blooded species. This highly successful parasite currently infects close to one-third of the human population. There are only three main strains of the parasite in nature and each line causes profoundly different disease in animals. Toxoplasma is known to stimulate a variety of immunological responses in infected hosts. Hosts are unable to clear the parasite, resulting in a life-long infection. Dr. Grigg is studying the immunological and molecular interactions that modulate Toxoplasma pathogenesis in an animal model of the disease, and identifying the virulence factors that are essential to the success of particular strains of the pathogen. From his work, he hopes to uncover new mechanisms and principles of pathogenesis.