In 2007 parasite immunologist P’ng Loke sat down for lunch at a University of California, San Francisco, cafeteria with a patient who wanted help documenting his medical condition. The two shared an unusual interest: gut worms—specifically, tiny wormlike parasitic organisms called helminths.

Loke’s 35-year-old guest, who declined to be identified for reasons of patient confidentiality, explained that he suffered from an inflammatory bowel disease known as ulcerative colitis. While researching his condition a few years before, the man had read about helminthic therapy, which has not been approved by the FDA but which is a subject of active research by gastroenterologists and parasitologists. The idea is that people with autoimmune disorders can ease their symptoms by deliberately infecting themselves with parasitic worms such as hookworm or whipworm, both of which supposedly pacify the human immune system to survive inside the body. In numerous animal studies, these parasites ostensibly protected rodents from a wide variety of immunological disorders, including colitis, asthma, rheumatoid arthritis, food allergies and type 1 diabetes. The man had convinced himself the therapy could work for him, and, since 2004, he had been ingesting whipworm eggs, which he obtained from Thailand. He was now virtually symptom-free. Could Loke help him figure out how, if at all, the worms had treated his colitis?

Loke was skeptical at first but agreed. In a recent paper published in Science Translational Medicine, Loke, now at New York University, and his colleagues suggest that the whipworms are indeed effective in treating colitis. Repeated colonoscopies, for example, showed that wherever worms colonized the patient's  colon, the signs of colitis—open sores and inflammation—were significantly reduced or nonexistent. More important, Loke showed through tissue analysis that the parasites may work by stimulating mucus production in the gut. Colitis, which is associated with decreased mucus production, is thought to occur when the immune system attacks benign bacteria living in the intestines. The extra mucus may help calm the immune system and prevent it from attacking the gut’s harmless microorganisms.

“This is not a double-blind study, but the pattern is highly suggestive that the worms helped this patient,” says Joel Weinstock, a gastroenterologist at Tufts University who has pioneered helminthic therapy research. “The major point of this paper is the potential mechanism—mucus production—which has not been looked at properly before.”