Could a worm a day keep the doctor away?

Swallowing the eggs of parasitic worms may seem the polar opposite of modern medicine. a growing body of research, however, is examining the stomach-turning possibility that parasites affect the immune system in a way that may protect against multiple sclerosis, inflammatory bowel disease, and other modern-day disorders.

Certain parasites have dwelled in people’s guts through much of human history.

Clinical trials are beginning to test whether intestinal worms have an effect on conditions such as food allergies and Crohn’s disease — problems blamed on a haywire immune responses. And researchers are trying to unravel exactly what worms do in the gut, in the hope that drugs could be developed to mimic the beneficial effects.

In the most recent work, published last week in the journal Science Translational Medicine, scientists followed a person with ulcerative colitis who saw his symptoms disappear after he swallowed the eggs of an intestinal parasite. using genomic tools and biopsies, scientists looked deep into his gut and identified one of the ways in which the worm might have helped.

“It’s not like the worm woke up one day and said, ‘What can I do to make you well?’ said Dr. Joel Weinstock, chief of gastroenterology at Tufts Medical Center. he was not involved in the new study. “when you live close with something throughout evolution, and then you suddenly remove something, there can be consequences,’’ he added. “Disturbing our intestinal worms, disturbing our intestinal bacteria, may modify or change our susceptibility to disease.’’

Scientists and clinicians caution that people should not intentionally infect themselves with a parasite; such research is in its earliest stages.

But the idea now being tested had its origins in the simple observation that autoimmune diseases, in which one’s own immune system attacks the body, are uncommon in developing countries, where infection with helminths — parasitic worms — is common.

In 2005, Weinstock reported in the journal Gastroenterology that in a clinical trial of pig whipworms in people with ulcerative colitis, there was a measurable therapeutic effect. Patients were randomly assigned to ingest the worms or a placebo.

That body of work motivated the 35-year-old patient whose case was reported last week to infect himself, said P’ng Loke, an assistant professor of medical parasitology at new York University and the study’s lead author. the patient’s disease had not responded to drugs, and he feared having the colon removed. the man traveled to Thailand and obtained eggs from a parasitologist. he swallowed 500, followed by a second dose of 1,000 eggs, and his symptoms subsided.

In 2007, he contacted Loke. Loke and his colleagues found that when the man’s disease went into remission, a particular protein involved in healing of the mucosal lining of the gut was prevalent. their measurements suggested the worms’ presence stimulated mucus production, which was disrupted in the disease. To Loke, that suggests it might be possible to recapitulate the worm response, a possibility he is investigating in mice.

Such research could also have an effect on other diseases.

Lisa Ganley-Leal, assistant professor of medicine at Boston University School of Medicine, has founded a Newton company called Epsilon Therapeutics to study whether mimicking a worm’s effect in the body could help allergy sufferers.

She has studied people in Africa who suffer from schistosomiasis, a disease caused by a worm that lives in fresh-water snails. she has found that exposed people have high levels of the antibody IgE, which normally causes allergies when it binds to cells. but the people she was studying had virtually no allergies.

In the laboratory, she found that the worms appeared to be chopping up a protein, which appears to prevent IgE from binding to cells to cause the allergy.

Dr. David Elliott, at the University of Iowa Carver College of Medicine, has studied worms’ therapeutic effects in mice. because the field captures people’s imaginations, he said, he is careful to warn patients to wait for “more in-depth investigation before it’s ready for prime time.’’

© Copyright 2010 Globe Newspaper Company.