Identifying Johne's Disease with accuracy

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Detecting the costly, contagious Johne's disease in cattle is now easier, thanks to USDA scientists.

Johne's disease, also known as Paratuberculosis, is estimated to cost the U.S. dairy industry more than $220 million each year. It also affects sheep, goats, deer and other animals, causing diarrhea, reduced feed intake, weight loss and sometimes death.

Microbiologist John Bannantine and his colleagues at the Agricultural Research Service (ARS) National Animal Disease Center (NADC) in Ames, Iowa, discovered an antibody that's 100 percent specific in detecting Johne's disease. This is the first time a specific antibody that binds only to Mycobacterium avium subspecies paratuberculosis (MAP), the pathogen that causes the disease, has been discovered. A patent has been awarded to scientists for the antibody, which could greatly benefit the improvement of diagnostic tests that confirm the presence of MAP.

Previous efforts to detect Johne's disease were hindered because all antibodies used to identify MAP strains also reacted to environmental mycobacteria, according to Bannantine, who works in NADC's Infectious Bacterial Diseases Research Unit. Some of those antibodies also reacted to the disease pathogen responsible for bovine tuberculosis (TB) and caused false-positive results.

Other research, conducted by NADC microbiologist Judy Stabel, focused on ensuring that Johne's disease vaccines do not cross-react with tests for bovine TB, a disease problem in states where wild deer infect cattle.

Stabel and her team vaccinated calves with an effective commercial Johne's vaccine to test cross reactivity with TB tests. They took blood samples for a year and then measured immune and serological responses of calves using novel TB tests.

Scientists found no cross reactivity with the TB serology tests, demonstrating that animals could be vaccinated against Johne's disease without interfering with bovine TB testing. Similar results were found with the skin test used to detect TB in cattle.

Read more about this research in the April 2013 issue of Agricultural Research magazine.



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