Nematode infections of the eye: toxocariasis, onchocerciasis, diffuse unilateral subacute neuroretinitis, and cysticercosis.

Nematode infections of the eye are common in different parts of the world, but some are usually encountered only in developing nations, such as onchocerciasis and cysticercosis. Ocular toxocariasis is a well-known cause of unilateral ocular disease affecting mainly children and young adults, and is usually caused by T canis. Prevention of ocular toxocariasis is based on such measures as appropriate health care for dogs and cats, including regular anthelmintic treatments, preventing contamination of the environment with feces, and promoting responsible pet ownership [1,49-51]. Onchocerciasis is caused by infection with the filarial parasite O volvulus, and occurs in endemic areas along rivers and streams. In hyperendemic areas almost every person is infected and about half of the population is eventually blinded by onchocerciasis. Because of this, elimination of host-vector contact is very important. DUSN is caused by a motile nematode and is found in the Southeastern and Midwestern United States and in many parts of the world. In Brazil, DUSN is becoming an important cause of posterior uveitis in children and young healthy adults. The destruction of the worm during the early stages of the disease can prevent progression of the visual loss. It is important to remain aware of this entity, not only in areas where it has been described, but also in regions not yet identified as being endemic [52]. Cysticercosis is caused by the encystment of the larvae of the tapeworm T solium, and usually results from ingesting eggs from food, water, or other material contaminated with human feces. Surgical removal of the cyst is usually indicated when possible.