Although it is less widespread than the pinworm, the whipworm is a cosmopolitan para-site, infecting approximately 1 billion people throughout the world. It is concentrated in areas where indiscriminate defecation and a warm, humid environment produce extensive seeding of soil with infectious eggs. In tropical climates, infection rates may be as high as 80%. Although the incidence is much lower in temperate climates, trichuriasis affects 2 million individuals throughout the rural areas of the southeastern United States. Here it occurs primarily in family and institutional clusters, presumably maintained by the poor sanitary habits of toddlers and the mentally retarded. Although the intensity of infection is generally low, adult worms may live 4 to 8 years.
Attachment of adult worms to the colonic mucosa and their subsequent feeding activities produce localized ulceration and hemorrhage (0.005 mL blood per worm per day). The ulcers provide enteric bacteria with a portal of entry to the bloodstream, and occasionally a sustained bacteremia results. A decrease in the prevalence of trichuriasis in the postadoles-cent period and the demonstration of acquired immunity in experimental animal infections suggest that immunity may develop in naturally acquired human infections. An IgE-mediated immune mucosal response is demonstrable in humans, but is insufficient to cause appreciable parasite expulsion.