No one knows what causes Crohn's disease, an inflammation of the small intestine that causes abdominal pain and makes it difficult to digest food. Genes may predispose a person to the disease, or it may have external causes. Twenty years ago, doctors realized that a particular type of bacteria, Mycobacterium avium, subspecies paratuberculosis (MAP), could be found in the blood of some patients with Crohn's disease. Since then, researchers have been struggling to figure out whether MAP is a cause of the disease, a result of it, or associated in some other way. Researchers from the University of Central Florida took a shot at figuring out how MAP fits into Crohn's disease.

What the researchers wanted to know: What role do the bacteria Mycobacterium avium play in Crohn's disease?

What they did: Fifty-two patients participated in the study, 28 with Crohn's, nine with ulcerative colitis (a related disease), and 15 without an inflammatory bowel disease. The researchers took blood samples from all of the participants and tested it for the MAP bacteria.

What they found: Half of the patients with Crohn's disease had MAP in their blood, two of the patients with ulcerative colitis had it in their blood, and none of the patients without inflammatory bowel disease had it in their blood. MAP had previously been identified in patients' intestines, lymph nodes, and breast milk, but this is the first time researchers have found it in the blood. Based on their own findings and previous research, the authors argue that MAP bacteria infect patients with Crohn's and potentially cause the disease. Other people are exposed to the bacteria in food and water, but their bodies do not seem to allow it to multiply. They believe that the patients with colitis who had MAP in their blood likely were misdiagnosed or have both Crohn's and colitis.

What it means to you: If this kind of bacteria is a cause of Crohn's, it may mean new approaches, such as antibiotics, to treat it. This is still a long way off, however, and the article doesn't prove that MAP causes Crohn's.

Caveats: In an accompanying editorial, an Australian doctor counters that their study only shows an association between the MAP bacteria and Crohn's; more work is needed to figure out if the bacteria are a cause or just one part of the disease.

Find out more: The Crohn's and Colitis Foundation of America has a lot of information about Crohn's, including a good general overview.

Read the article: Naser, S.A. et al. "Culture of Mycobacterium avium Subspecies Paratuberculosis From the Blood of Patients With Crohn's Disease." The Lancet. Sept. 18, 2004, Vol. 364, No. 9439, pp. 1039-1044.

Abstract online: www.thelancet.com