The epidemiology of Toxocara canis

Bred as hunter, companion and pet, the dog has a long and honourable association with man. Yet the domestic dog can host a wide range of parasites - many of which can also infect humans. One of these, the ascarid nematode Toxocara canis (Fig. 1), is of particular interest because of retinal damage that may result from larvae becoming trapped in the eye. At the Hospital for Tropical Diseases in London, about 20-30 patients with toxocariasis are treated annually. Widespread fouling of public parks, playgrounds and pedestrian areas with dog faeces - especially in large cities - is well -recognized as one of the main sources of Toxocara infection. Yet as Stephen Gillespie discusses here, epidemiological indicators vary widely and the risk of infection is often treated too lightly.