Ocular involvement in toxoplasmosis.

Toxoplasmosis is a major and preventable cause of severe visual handicap and blindness in young people. Congenital toxoplasmosis, as well as toxoplasmosis in immuno-compromised patients, is a serious, sometimes fatal disease. I 2 Toxoplasmic encephalitis has gained importance as a leading cause of AIDS related mortality. Toxoplasma gondii, the aetiological agent of human and animal toxoplasmosis, is ubiquitous in nature. The organism is an obligate intracellular parasite and its definitive host is the cat. Oocysts, which are excreted in cat faeces, are highly resistant and may remain infective for more than 1 year. Usually only young cats are infected for a short period of time. The infected cat is not the primary source of infection for humans but is a very important cause of contamination of the environment (soil, fruit, and vegetables and thus other infected animals which become intermediate hosts). Toxoplasma gondii is the most important protozoan cause of intraocular inflammation owing to its widespread distribution throughout the world, the frequency of ocular involvement, and the seriousness of the symptoms it may cause. Toxoplasmosis was first recognised in patients with congenital disease: in 1923 Janku' in Prague presented the first report on a boy who became blind at the age of 3 months and died ofhydrocephalus; a granulomatous inflammation of the eye with protozoa in the retina was found.3 Wolf subsequently verified the aetiology by recovering the Toxoplasma and transmitting the infection to animals.4 Retrospective analysis of specimens has demonstrated the disease in a large number of patients with neonatal encephalitis, thus emphasising the possibility of toxo-plasmosis in such cases.5 The major problem in diagnosing ocular toxoplasmosis in adults was the difficulty of establishing the presence of the parasite in ocular lesions. Helenor Wilder provided proof by demonstrating organisms with the morphological characteristics of Toxoplasma gondii in the eyes of patients with chorioretinitis, who had undergone enucleation because of blindness and pain.6 Human infection may occur by either the congenital or the acquired route. Acquired disease usually develops after ingestion of oocysts or tissue cysts and almost all cases (in immunocompetent individuals) are asymptomatic. The prevalence of seropositivity due to a previous Toxoplasma infection varies among different populations, depending on eating habits, climate, etc. In the Netherlands the majority of the population has already been infected by the age of 40 years.7 Congenital infection can occur when a pregnant woman becomes infected; during the parasitaemia, Toxoplasma crosses the placenta …