Ocular Toxocariasis

Toxocara canis/cati are parasitic nematodes that resides in the small intestine of dogs, cats and wild carnivores. They are found worldwide. Female worms are approximately 10 cm long and produce hundreds of embrionated eggs per day. Following several weeks in the environment, the embryo matures to the infective larval stage within the egg. It can remain viable for very long periods of time. The prevalence of Toxocara eggs in the ground is related to the number of dogs in that area and climatic factors of the country. Human infection is due to accidental ingestion of infective eggs and tissue invasion of second stage Toxocara cati or canis larvae. Transmission is by contaminated food o by geophagia. Children up to 10 years are more prone to be infected for both their common geophagia. Eighty per cent of pets are infested, and the incidence may vary in different countries (London 33%, Columbus – Ohio 98%, Brisbane – Australia 100%). Human infection may be asymptomatic, it may simulate a viral infection or determine visceral larva migrans syndrome. The average age of onset is between 1 and 5 years and it has no correlation with concomitant ocular involvement. In only 2% of the cases of ocular toxocariasis it is possible to find a history positive for visceral larva migrans syndrome. The incidence of ocular toxocariasis is undetermined and it may vary according to different Authors and in different countries. It is more frequent in children and it constitutes 1-2% of uveitis in children. Toxocara should be considered as a possible causative agent of posterior and diffuse uveitis and always in the differential diagnosis of retinoblastoma. The average age at diagnosis of ocular toxocariasis is 7.5 years (ranging from 2 to 31 years) and 80% of the patients are younger than 16 years old. [1] We can find three different manifestation of ocular involvement: chronic endophthalmitis, posterior granuloma and peripheral granuloma which clinical findings are reported in table 1.