Ocular Toxoplasmosis

Address for Correspondence: Dr. Jyothirmay Biswas, Head of the Department of Ocular-Pathology and Uvea, Medical and Vision Research Foundations, Sankara Nethralaya, 18, College Road, Chennai-600 006, E-mail: [email protected] Toxoplasmosis is the most common cause of posterior uveitis in many parts of the world. Prevalence is more in tropical countries than cold areas. 1,2 It is caused by Toxoplasma gondii, an obligate intracellular protozoan parasite which exists in three forms : oocyst, bradyzoite and tachyzoite. Tachyzoites are the invasive forms, bradyzoites are the encysted forms and sporozoites (oocysts) exist in the cat only. Cats are the definitive hosts where as humans and other animals act as intermediate hosts. Human infection by T.gondii can be acquired or congenital. The transmission occurs by ingestion of raw or undercooked meat infected with tissue cysts, ingestion of food and water contaminated with oocysts , ingestion of eggs and milk contaminated with tachyzoites, blood transfusion, organ transplantation and transplacental transmission. 1,2 T. gondii can also rarely be transmitted via blood and infections of laboratory personnel through contact with contaminated needles.