PURPOSE: To update clinical information about ocular toxoplasmosis. Part I reviews information about prevalence of disease, sources of infection, relation of ocular disease to time of Toxoplasma gondii infection (congen-ital vs. postnatally acquired), and course of disease. DESIGN: Literature review. METHODS: Selected articles from the medical literature, information from recent scientific meetings, and the author's personal experiences were reviewed critically in preparation for the LX Edward Jackson Memorial Lecture. RESULTS: The prevalence of T. gondii infection varies geographically and increases with age; in the United States, the overall proportion is 22.5%. The proportion of infected individuals in the United States who have had episodes of ocular toxoplasmosis is unknown, but may be approximately 2%. Prevalence of ocular involvement is substantially greater in other parts of the world, including southern Brazil. In addition to undercooked meat and unwashed vegetables, drinking water contaminated with oocysts may be an important source of infection in some settings. In contrast to traditional teaching, evidence suggests that most individuals with ocular toxoplasmosis were infected postnatally. Ocular lesions may first develop many years after T. gondii infection. The risk of recurrent ocular disease appears to be greater during the first year after an episode of toxoplasmic retinochoroiditis than during subsequent years. CONCLUSIONS: Reassessment of older publications in the light of recent observations provides a richer under, standing of ocular toxoplasmosis, although knowledge about the disease remains incomplete. A better understanding of the clinical characteristics and course of ocular toxoplasmosis will have important implications for developing more effective prevention and treatment strategies. (C) 2003 by Elsevier Inc. All rights reserved.
