Biology and immunology of human strongyloidiasis.

Strongyloidiasis is an important human parasitic infection primarily because of its potential for serious and even lethal disease in immunosuppressed patients. Certain features of the biology of Strongyloides stercoralis, such as the ability to autoinfect the host, help explain why the parasite is dangerous. Characteristics of the parasite can also be exploited in parasitological diagnosis of infection with the Baermann concentration procedure and by culture. Use of filariform larval antigens in ELISA or immunofluorescent-antibody tests now provide reliable serological tests for diagnosis, and, in most patients, antibody levels decline one to two years after successful treatment. Immediate hypersensitivity is a prominent component of the immune response to strongyloides infection and may play a role in the pathogenesis of disease as well as in protection. An IgE-mediated skin test appears to be useful in diagnosis. Animal models used for immunologic studies of other intestinal helminths have lacked relevance to human strongyloidiasis. Features of the human disease, however, including hyperinfection syndrome, can be produced by S. stercoralis in the Patas monkey and in dogs.