Roundworms, or nematodes are important causes of diseases in animals, yet relatively little is known about how they sustain themselves in the animals that they infect. Our research aims to elucidate and exploit the ways by which the host's immune response interferes with parasitism by nematodes. We are currently studying two important pathogens, Trichinella spiralis and Parelaphostrongylus tenuis. The latter organism is a significant cause of disease in sheep, goats and llamas in the Northeast. Our goals for the P. tenuis work are twofold: first, to develop an antigen detection test for use in diagnosis, and second, to design vaccines to prevent infection. Our interest in T. spiralis concerns the most fundamental question in infectious disease, specifically, how does one organism parasitize another?