Doctors who treat patients with Crohn’s disease have long regarded the illness as a biological version of friendly fire, where people’s own immune systems mistakenly attack the digestive tract. But Washington State University researcher William Davis said its cause may originate outside the human body - from a germ that sickens cattle.

Working with scientists internationally, Davis is developing a vaccine that could head off the problem.

Why a rod-shaped bacterium that infects cattle is turning up in the intestines of humans warrants far more investigation than it is getting, said Davis, a professor in WSU’s Department of Veterinary Microbiology and Pathology. A new vaccine could save cattle, the livelihood of dairy farmers and ranchers, and lend a measure of protection to humans against the potentially harmful germ, he said.

That germ, Mycobacterium avium subspecies paratuberculosis, or MAP, is related to the microbe that causes tuberculosis.

It causes Johne’s (pronounced yo-nees) disease in the intestines of cattle and other ruminants. This produces symptoms similar to those experienced by people with Crohn’s disease, including drastic weight loss, chronic diarrhea and malnutrition, according to numerous studies on the two disorders.

Big implications

MAP has infected a staggering number of cattle during the past 100 years. It is secreted in their feces and milk, said Davis, who has been researching the bacterium for two decades. In 2003, he co-authored a report for the National Academy of Sciences on its diagnosis and control.

So when it was identified in the intestines of humans, he and scientists from Canada to Europe paid attention. The theory that it might be making people sick is controversial. If proven, it means modern medicine’s understanding of Crohn’s disease is incorrect and a harmful bacterium is being transmitted via the human food chain.

"We know the incidence of Johne’s is on the rise, as is the incidence of Crohn’s,” said Davis, whose research has included collaboration with physicians and immunologists. "The problem is too important and the theory is sufficiently plausible that we need to be taking a closer look. More research is necessary to resolve exactly what the link is.”