A few years ago, a 35-year-old man in California had extensive ulcers in his colon. He was diagnosed with ulcerative colitis, an inflammatory bowel disease, and doctors recommended removing part of his colon. So he swallowed over a thousand parasitic worm eggs from Thailand, and just over a year later, his ulcers were gone.
Ulcerative colitis is a chronic inflammation of the mucous membrane (or mucosa) that lines the colon, and symptoms include open sores in the lining of the colon, abdominal pain, bloody diarrhea, and rectal bleeding. What causes it remains unknown, but the disease has been linked to defects in regulation of the immune system.
The disease is more common in economically developed countries; over 500,000 Americans are affected by it. The drugs that supposedly treat it don’t always work and can cause serious side effects, and doctors sometimes recommend cutting out parts of the colon altogether.
However, this disease is rare in Asia, Africa, and Latin America, where parasitic worm – or helminth – infections are common. Heavy worm infestation, especially in children, can cause dysentery and lead to growth retardation and reduced cognitive function. Parasitic worms control the immune response of their hosts in order to survive within the host gut.
This geographic association led researchers to suspect that parasitic worms may offer protection or at least provide relief against bowel disease.
Known as “helminthic therapy," ingesting these squirmy parasites has alleviated other conditions like Crohn’s disease, multiple sclerosis, rheumatoid arthritis, and asthma.
“The idea for treating colitis with worms is not new, but how this therapy might work remains unclear,” said medical parasitologist P’ng Loke of New York University Langone Medical Center who led the study. In animal tests and clinical trials, these worms have suppressed inflammation.
So in early 2004, a man deliberately swallowed 1,500 eggs of the human whipworm (Trichuris trichiura) to treat his ulcerative colitis symptoms. This parasitic roundworm infects the large intestine in about a billion people worldwide. He drank them from a vial of salty liquid.
The eggs hatched and the parasites nested themselves in the walls of his intestine. Loke’s team investigated the medical history and tracked the progress of this man, taking blood and tissue samples before and after the worm swallowing.
Before, tissue afflicted with ulcerative colitis had high numbers of immune cells that produce a particular inflammatory protein (IL-17) but not another (IL-22).
About a year after ingesting worm eggs, his bowel disease went into remission and lots of cells producing IL-22 popped up in his colon tissue; these IL-22 producing cells are important in healing the mucous lining of the intestines.
The presence of the worms probably activated an immune response, where IL-22 cells increased mucous production in the colon. “Basically,” Loke said, “the gut is trying to expel the worms.”
“It's possible the mucus serves as a defensive barrier between bacteria and the gut that prevents bacteria from causing inflammation and crossing over into other tissues,” Loke said.
The worms, it would appear, were beneficial bystanders, unintentionally increasing mucus production in the colon to repair the damaged mucous lining and reduce the symptoms of ulcerative colitis.
“In essence, the worms trigger a big sneeze of the gut, which may have a beneficial side effect,” said Loke, who does not advocate helminth therapy because these worms themselves can cause harm and damage the gut. “The individual in this study is lucky to have responded so well, but for other people the worm infection may exacerbate bowel inflammation.”
As the number of eggs found in the patient's stool diminished, his symptoms began to return. When his tissue became inflamed again three years later, he reinfected himself with 2,000 eggs and got better again.
But as Loke reminds us, “you can't tell with a sample size of one.” Loke plans to continue researching helminthic therapy in people and monkeys.
Image (top): Trichuris trichiura eggs in ulcerative colitis patient / Kimberley Evason, UCSF
Image (bottom): Colon infected with Trichuris trichiura / Uma Mahadevan, UCSF