By Pat Anson, Editor

Many of us were taught as children to always wash our hands before leaving the bathroom and before meals. But that basic sanitary practice may be contributing to an increase in inflammatory bowel diseases (IBD) such as Crohn’s disease and ulcerative colitis, according to a new study published in the journal Science.

Researchers at New York University’s Langone Medical Center tested the so-called “hygiene hypothesis” – the theory that some intestinal parasites and bacteria are beneficial because they help balance the immune system and reduce IBD rates. Sanitary practices have sharply reduced gut worm infections in developed nations, which now have some of the highest rates of Crohn’s disease and ulcerative colitis.

“Our findings are among the first to link parasites and bacteria to the origin of IBD, supporting the hygiene hypothesis,” says parasitologist P’ng Loke, PhD, an associate professor at NYU Langone.

“The prevalence of IBD is much less in regions of the world which have heavy worm infection. In fact, I got interested in the question of how worms can be beneficial when I was contacted by an individual who had deliberately infected himself with worms to treat his symptoms of IBD and was able to put his disease into remission.”

Loke and his colleagues found that laboratory mice infected with intestinal worms experienced a thousand-fold decrease in Bacteroides — a type of bacteria linked to people with higher risk of IBD. At the same time, the number of Clostridia, a bacterium known to counter inflammation, increased tenfold in the mice.

Researchers believe the immune response to the worms triggers the growth of Clostridia, which then either outcompete Bacteroides for nutrients or release toxins that are harmful to them.

In a second phase of the study, researchers gave mice an infusion of Clostridia – without the use of parasites – and found that it reduced the presence of Bacteroides.

“That gives us a lot of hope in terms of IBD therapy because maybe we don’t need to give people parasitic worms, which can be harmful and cause disease, and instead target the harmful bacteria by replacing them with healthy bacteria,” says microbiologist Ken Cadwell, PhD, an assistant professor at NYU Langone and the Skirball Institute of Biomolecular Medicine. “Our study could change how scientists and physicians think about treating IBD.”

Researchers say the hygiene hypothesis may also apply to other autoimmune diseases, including multiple sclerosis, rheumatoid arthritis, and type 1 diabetes, in which processes meant to attack foreign invaders instead become oversensitive and trigger an immune response to the body’s own cells.

IBD is a chronic or recurring immune response and a painful inflammation of the gastrointestinal tract. Inflammation affects the entire digestive tract in Crohn’s disease, but only the large intestine in ulcerative colitis.

According to the Crohn's and Colitis Foundation of America, IBD affects about 1.6 million Americans and tends to run in families. Caucasians are more likely than other ethnic groups to have IBD. The diseases are especially prevalent in Jews of European descent (Ashkenazi Jews). African Americans and Hispanics in the United States are also increasingly affected.