New Diagnostic Tool Will Aid in Eradicating Cattle TuberculosisBy
A new diagnostic test takes only 2 to 3 days to detect the bacterium that
causes cattle tuberculosis, an improvement over current diagnostic methods that
take 2 to 3 months.
Mycobacterium bovis--the culprit in cattle tuberculosis--is very
similar to two other bacteria: M. avium and M. paratuberculosis.
The inability to distinguish between these similar organisms has slowed down
the U.S. Department of Agriculture's goal of
eradicating cattle tuberculosis by the year 2000.
Scientists with USDA's Agricultural
Research Service in Ames, Iowa, developed the new diagnostic test at the
request of USDA's Animal and Plant Health
Inspection Service (APHIS). APHIS works with state animal health inspection
agencies and U.S. livestock producers to eradicate cattle TB.
The test uses polymerase chain reaction (PCR), a technique that makes
millions of copies of targeted genetic material found only in M. bovis.
Making so many copies of the targeted DNA allows easy identification of M.
bovis, which couldn't be seen before the PCR amplification. Extensive tests
in other laboratories have proven that this piece of DNA isn't present in other
The researchers checked the PCR test by examining 99 known cases of TB in
cattle and elk. In 93 percent of the cases, they could make an accurate
diagnosis within 2 to 3 days after receiving the tissue samples. The speedier
diagnosis will allow APHIS officials to take immediate action to identify the
most common sources of cattle tuberculosis: imported Mexican steers, the
captive elk and deer population, and large dairy herds with low levels of
Bovine TB spreads among animals when they cough and release the bacteria
into the air. Human tuberculosis is caused by a different bacterium, M.
tuberculosis, although M. bovis can also infect humans. Milk
pasteurization kills the TB-causing bacteria. When pasteurization standards were
developed in the 1920's, M. bovis and M. tuberculosis were
considered the most resistant pathogens.
Scientific Contact: Janice M. Miller, USDA-ARS
National Animal Disease Center,
Ames, Iowa, phone (515) 239-8316, fax 239-8458,