Monday, July 11, 2011

Ocular Toxocariasis

Ocular toxocariasis is an eye condition caused by migration of Toxocara canis or Toxocara cati parasitic larva into the back segment of the eye. This eye disease usually occurs in children and teenagers. People get infected with Toxocara when they unintentionally ingest embryonated eggs that have been shed in the feces of infected animals. Since the eye retina is severely affected, ocular toxocariasis may cause blindness. In young patients, the eye infection may not be noticed until they fail a school vision screening test, or develop strabismus or leukocoria. In ocular toxocariasis, the major causes of visual acuity loss are: severe vitreitis (52.6% of the cases), cystoid macular edema (47,4%), and tractional retinal detachment (36.8%). Patients may present with decreased vision, red eye, or leukokoria (white appearance of the pupil). Granulomas and chorioretinitis can be observed in the retina, especially at the macula.

Toxocara canis or 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.