Intestinal issues are not just for humans. Rhesus macaques living in captivity often develop chronic diarrhea similar to the human autoimmune condition ulcerative colitis. Now these animals are providing new insights about a cure for this condition in both species—and that cure is worms.

Small human trials have found that giving people pig whipworm eggs can reduce symptoms of inflammatory bowel disease (IBD). In developing countries where IBD is much less common, parasitic worms (helminths) are often endemic, perhaps conferring some benefit. But scientists have still been parsing out why the presence of these worms might work so well.

For the new study, P'ng Loke, an assistant professor of microbiology at New York University Langone Medical Center, and his colleagues selected five juvenile rhesus macaques with idiopathic (cause unknown) chronic diarrhea. Each monkey was fed 1,000 parasitic whipworm (Trichuris trichiura) eggs. After the treatment, four of the five monkeys had improved and regained weight. The findings were published online in PLOS Pathogens.

The researchers found that the ill monkeys started out with an abnormally high rate of bacteria attached to the mucosal membranes of their colon. After the treatment, bacterial communities in their colon had changed substantially, suggesting that exposure to helminths may help restore the balance of microbial communities in the gut.

The team speculated that the presence of the parasite eggs stimulated extra mucus production and healing, in addition to renewing epithelial cells, which line the gut. These changes helped to reduce the quantity of bacteria that could attach to the gut lining and rev up the immune response unnecessarily. Loke and his colleagues are now starting a human trial to test pig whipworm eggs as a treatment for ulcerative colitis. If it proves successful and eventually makes it to market, just think of them as the caviar of probiotics.