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For years now, there's been evidence that intestinal parasites can actually be a good thing for people with inflammatory bowel disease. That's because certain parasitic worms seem to help the intestine heal. Now, scientists think they've found at least one reason why this is so, thanks to a man who spent years treating his own bowel disease with worms.

NPR's Jon Hamilton has the story.

JON HAMILTON: P'ng Loke studies parasites. Years ago, when he was working at the University of California, San Francisco, he got a call from a stranger.

Mr. P'NG LOKE (Research Scientist, Langone Medical Center, New York University): He had moved into the Bay Area and was looking for someone who works on worms, and so he called me and convinced me to have lunch with him.

HAMILTON: Over lunch, the man told Loke a remarkable story about how he'd recovered from ulcerative colitis. It's a bowel disease in which the immune system appears to attack the lining of the colon, causing devastating ulcers. And for this man, the usual treatments, including steroids, hadn't helped.

Mr. LOKE: So he was being faced with the options of really severe immune suppressants or colectomy.

HAMILTON: The doctors wanted to remove his colon. But this man was a young entrepreneur with his own ideas. He'd run across the work of a scientist named Joel Weinstock.

Weinstock, who's at Tufts Medical Center in Boston now, had done something that seemed bizarre. He'd started treating people with ulcerative colitis using parasitic worms.

Dr. JOEL WEINSTOCK (Tufts Medical Center Gastroenterology/Hepatology Division): So people would swallow microscopic eggs and the eggs then hatch within the GI tract and that living agent comes out, is capable to interact with the host immune system.

HAMILTON: Weinstock thought these parasites might help because in parts of the world where they are common, inflammatory bowel disease is rare. And his hunch turned out to be correct. The people in his study got better. Loke says that was good enough for the entrepreneur in San Francisco who started looking for his own source of parasitic worm eggs.

Mr. LOKE: And he managed to find a parasitologist in Thailand who was willing to help him obtain these eggs, and then he infected himself.

HAMILTON: He got better too. And he was feeling fine by the time he had lunch with Loke. But he wanted scientists to figure out why the cure had worked. So he offered to let researchers study his intestine over the next few years. During that time, the worms began to die off and the man's disease came back. So he took another dose of worm eggs and got better again. Through it all, Loke and his colleagues were collecting blood and tissue samples from the man.

Mr. LOKE: And what we found was that after worm infection, the regions of the colon that were previously not making mucus was now making mucus again.

HAMILTON: That's a key factor in healing. And it looked like the mucus came back because the worms were causing the body to produce a substance called IL-22. Weinstock says that makes sense.

Dr. WEINSTOCK: This is a molecule that promotes epithelial growth and healing and perhaps does other things to the immune system that would be potentially beneficial.

HAMILTON: Weinstock says other studies suggest parasites can regulate the immune system in ways that prevent it from going wild and attacking healthy tissue. And he says it's likely that human evolution took that into account.

Dr. WEINSTOCK: Humans have had parasites ever since we evolved from living in caves and - or swinging from trees or however it used to be, and disrupting these relationships probably had consequences.

HAMILTON: Weinstock says drug companies are now trying to create parasites that would actually be approved by the FDA for treating inflammatory bowel disease.

These days, Loke is in New York, at NYU Medical Center. He says the entrepreneur in San Francisco plans to keep himself infected with parasitic worms. The new research appears in the journal Science Translational Medicine.

Jon Hamilton, NPR News.

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