2010 Annual Report 1a.Objectives (from AD-416) Define molecular basis of toxoplasmosis. 1b.Approach (from AD-416) T. gondii strains of different genetic background will be isolated and cultured. 3.Progress Report Toxoplasma gondii is an extremely common parasite of animals that also infects humans, leading to widely different clinical outcomes, although the reasons for this variability are uncertain. Certain Toxoplasma genetic types were associated with clinical toxoplasmosis in humans and mice. We have obtained numerous viable isolates of Toxoplasma from domestic and wild animals from many countries, including USA. These isolates are now been genetically characterized to better understand the genetic basis of pathogenicity.