Ulcerative colitis is a serious, debilitating disease in humans. For unknown reasons, this disorder is more common in Western countries than in developing countries. One possible explanation is that it results from both genetic and environmental risk factors that lead to an abnormal immune response to normal luminal flora. In this double-blind, placebo-controlled clinical trial, the investigators evaluated the efficacy and safety of treatment with Trichuris suis in people with ulcerative colitis. Fifty-two of 54 people completed the study; 30 were treated with helminthic ova and 24 with placebo. Patients were assessed every 2 weeks with the Ulcerative Colitis Disease Activity Index, which assesses stool frequency, severity of bleeding, mucosal appearance, and physician's overall assessment of disease activity. A statistically significant difference was found between ova- and placebo-treated patients at 12 weeks. Stool examination showed no ova, and investigators reported no adverse effects or complications. Humans are not a natural host for T. suis, so no diseases are associated with this infection. The investigators concluded that T. suis provides a safe and effective therapy for patients with ulcerative colitis, although the mechanism of action is still unknown.

COMMENTARY: That inflammatory bowel disease is far more common in people living in western countries than in developing countries has led to the theory that helminth parasites, which are more common in developing countries, somehow alter the intestinal immunologic response to antigens. To test this theory, Bob Summers and his group at the University of Iowa conducted an open trial, which I commented on in this section last year, showing that oral administration of T. suis ova helped people with Crohn's disease. Now, in a controlled trial they have taken it one step further and shown a response in patients with ulcerative colitis. They speculate that this aberrant parasite stimulates the intestinal immune system through a Th2 response associated with the production of IL-4 and IL-13, which impairs the development of Th1 cells. Excessive Th1 responsiveness is an important component of inflammatory bowel disease that, on a basic level, results from an imbalance of mucosal immunity. Thus, parasites may be important in intestinal immune balance! Only time will tell if we can use this information in veterinary medicine.

Trichuris suis therapy for active ulcerative colitis: A randomized controlled trial. Summers RW, Elliott DE, Urban JF, et al. GASTROENTEROLOGY 128:825-832, 2005.