Protozoal infections

Abstract

Protozoa are single-celled eukaryotic microorganisms. Certain species cause disease of the eye or periocular tissues either by direct infection or by the indirect effect of vascular complications. General Remarks Toxoplasmosis is a common and usually asymptomatic infection caused by the protozoan Toxoplasma gondii. In 1923, Janku described a retinal macular coloboma of a 11-month-old child, but it was not until the late-1930s when T. gondii organisms were isolated from a child with congenital toxoplasmosis and similar retinal lesions (47,82). Toxoplasma was transmitted to laboratory animals, and toxoplasmosis was recognized as a widespread disease affecting humans (82). In 1952, Wilder described organisms indistinguishable from T. gondii in 53 eyes from adults, who had been previously diagnosed histopathologically as having tuberculous choroiditis or syphilis (82). Subsequently, 21 of these patients were found to have positive serology for T. gondii (46). These findings led to the recognition that focal retinochoroidal scarring in adults is most likely due to toxoplasmosis.