Crohn's Disease and Mycobacterium Paratuberculosis

A bacteria that infects cattle may have a role in Crohn's disease

Patient groups and the dairy industry are calling attention to a disease that affects 1 in every 5 herds of cattle in the U.S. and is theorized to have a connection to Crohn's disease. It's still not known if there is, indeed a connection between a bacteria found to infect cows and inflammatory bowel disease (IBD). However, it is a topic that is very much of interest to patients and researchers.

Close-up of a cow in a field
Tony C French / DigitalVision / Getty Images

What Is Johne's Disease?

Johne's (YO-nees) disease is caused by the bacteria Mycobacterium paratuberculosis and is estimated to cost the dairy industry $200 to $250 million dollars a year. Eradicating Johne's would entail testing to identify diseased cattle in order to destroy them. It's estimated that as many as 68% of dairy herds are infected with Johne's disease.

An infected cow exhibits symptoms of diarrhea and weight loss as the bacteria attack her ileum. Rarely fever or abdominal pain (difficult to ascertain in animals) are also symptoms. As the disease progresses, the rest of the digestive tract is affected. Eventually, the bacteria spread to lymph nodes and into the bloodstream. When an infected cow is discovered, she is often sent to slaughter — that is, turned into steaks and hamburger.

How Cattle Are Infected

The bacteria causing Johne's is shed by the infected cow into her milk. The current pasteurization method is based on High Temperature, Short Time (HTST). This means that the milk is heated to 162 F for 15 seconds. The time period of 15 seconds has been shown to be insufficient to kill all of the paratuberculosis bacteria, which has a thick, waxy cell wall. As a result, paratuberculosis could live through the pasteurization process and be in cartons of milk on grocery store shelves. In fact, researchers found that up to 25% of milk on store shelves in central and southern England contained paratuberculosis DNA.

Johne's disease is not limited to cattle. It can also infect other animals such as sheep, primates, and according to Scottish scientists, rabbits, foxes, stoats, weasels, mice, and voles. It is theorized that these animals contract the disease from infected livestock, but it is not known if they can pass the bacteria back to livestock.

Link to Crohn's Disease

A controversial theory is that paratuberculosis can also cause Crohn's disease in humans. In 1984, unclassified Mycobacterium strains were isolated from 3 different Crohn's patients. In 1991 it became possible to positively identify these three strains as all belonging to M. paratuberculosis. In 1992 another study was conducted on intestinal tissue removed during surgery from 40 Crohn's, 23 ulcerative colitis, and 40 non-IBD patients. 65% of the Crohn's patient samples contained M. paratuberculosis, contrasting with only 12.5% of non-IBD patients. The researchers concluded that M. paratuberculosis does "play an etiological role in some cases of Crohn's disease."

In 1998 the National Institute of Allergy and Infectious Diseases (NIAID) held a workshop to take recommendations for further research into the link between M. paratuberculosis and Crohn's disease. The participants agreed that more scientific evidence is needed to either prove or disprove that M. paratuberculosis can cause disease in humans. Several points for further research were identified.

Next Steps In Research

The patient advocacy group, Paratuberculosis Awareness and Research Association, Inc (PARA), has played a significant role in bringing attention to this issue. In March 2001, Cheryl Miller, Co-executive Director of PARA, testified before the U.S. Congress House Appropriations Subcommittee on Labor, Health and Human Services, and Education asking them to set aside money for the purpose of researching Crohn's disease.

These developments are the focus of some research into the potential cause for Crohn's disease. It's now thought that IBD is actually hundreds of diseases, and there may be as many different causes.

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By Amber J. Tresca
Amber J. Tresca is a freelance writer and speaker who covers digestive conditions, including IBD. She was diagnosed with ulcerative colitis at age 16.