This protocol offers diagnosis and standard medical treatment for various parasitic gastrointestinal infections. Gastrointestinal parasites are either worms (helminths) or one-celled animals called protozoans which live in the human intestines. Often, parasitic infections do not cause illness. In these cases, drug treatment is not indicated, because treatment can have adverse side effects. Patients will be examined for their immune responses, correlation between the number of parasites and disease, and other studies.

Individuals with known or suspected parasitic diseases of the gastrointestinal tract, including amebiasis, giardiasis, hookworm, strongyloidiasis, trichuriasis, pinworm, tapeworm, trichinosis, clonorchis, opisthorchis, coccidiosis, paragonimiasis, and echinococcus may be eligible for this study.

Patient evaluations may include blood and urine tests, stool examination, X-rays, ultrasound studies and, uncommonly, duodenal aspiration for examination of fluid from the duodenum (first part of the small intestine). Other tests may be required, depending on the parasite and disease. Direct examination of the tissues of the intestines may be required to rule out certain infections.

Research procedures include collection of stool, blood and duodenal fluid when the diagnosis has been established and these procedures are not required for medical care. Patients with strongyloidiasis may also be given a diagnostic skin test similar to skin tests for tuberculosis and allergies. Research procedures on children will be limited to collection of stool, urine and blood. No more than 7 milliliters (1 1/2 teaspoons) per kilogram (2.2 pounds) body weight of blood will be collected in children over a 6-week period. In adults no more than 30 tablespoons of blood will be collected in a 6-week period.

Parasites may fail to respond to treatment. In these cases, it may be necessary to grow the parasite in the laboratory in order to test treatments in the test tube. Patients who do not respond to standard medications and dosing may need different doses of drugs or drugs or combinations of drugs used in the United States for other medical problems. If these medications or doses are used, patients will be informed of their possible side effects.