Researchers develop strategies to stop TB infections in cattle

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Improving tests and vaccination methods are some of the strategies U.S. Department of Agriculture (USDA) scientists are using to overcome obstacles that prevent the eradication of bovine tuberculosis (TB) in cattle worldwide.

Scientists at the Agricultural Research Service (ARS) National Animal Disease Center in Ames, Iowa, are developing new methods to prevent and control TB in cattle and white-tailed deer. ARS is USDA's principal intramural scientific research agency, and this research supports the USDA priority of promoting international food security.

Veterinary medical officers Ray Waters and Mitch Palmer and microbiologist Tyler Thacker are collaborating with international groups, other U.S. government agencies, the cattle industry and private companies to combat TB. They are developing better tests to help producers identify and remove TB-infected cattle from herds and keep healthy animals.

The tuberculin cattle skin test has helped eradication efforts, but has drawbacks, such as a 72-hour waiting period for results, according to Waters. Interferon-gamma release tests require live white blood cells that must be processed quickly. Traditional serum tests would be more convenient and less expensive.

Scientists demonstrated that improved antigens—substances that cause the immune system to produce antibodies against foreign bacteria—are crucial in developing effective serum tests. These findings were instrumental in the recent development of a new serum TB test by IDEXX Laboratories, Inc., of Westbrook, Maine.

Another type of test, based on polymerase chain reaction (PCR) analysis of DNA, has been developed by Thacker. The new PCR test detects Mycobacterium bovis, the causative agent of bovine TB, in fresh tissues. It is quicker, accurate and helps distinguish between M. bovis and environmental mycobacteria, which can cause false-positive results.

Scientists also tested a century-old TB vaccine, Bacillus Calmette-Guerin (BCG), in deer. Palmer and his colleagues fed a BCG oral bait vaccine to captive deer and examined them one to 12 months later to determine how long the vaccine remained in the deer. BCG was not detected in deer given a standard dose.

Deer that received elevated dosages—10 times the standard—had traces of BCG in lymph nodes and other tissues not commonly used for food. The vaccine was never found in common cuts of deer meat in any of the safety experiments.



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