Two of the most contagious and costly diseases of cattle—bovine tuberculosis (TB) and Johne's disease—have something in common: Both are caused by mycobacteria.
Some species of mycobacteria can cause serious illness and sometimes death in animals as well as humans. The pathogen responsible for Johne's disease is M. avium subspecies paratuberculosis (MAP), and the cause of bovine TB is M. bovis.
At the Agricultural Research Service (ARS) National Animal Disease Center (NADC) in Ames, Iowa, scientists are drawing up new battle plans to help control bovine TB and Johne's disease by developing and improving diagnostic tests, vaccines and other technology to detect and prevent the spread of disease.
New Tests for Bovine TB
Great progress has been made to eradicate bovine TB in U.S. cattle, and infection rates are low. However, M. bovis still persists in wildlife, which can transmit it to cattle. In addition, more reliable tests are needed to detect TB-positive cattle from Mexico before they are imported into the United States.
"While the diagnostic tuberculin skin test for cattle is helpful in slowing the spread of bovine TB, it is not sensitive enough, and requires a 72-hour waiting period for results," says NADC veterinary medical officer Mitch Palmer.
Also, the skin test may not be able to detect all TB-positive animals in a large herd, he says. When an animal is infected with TB, the entire herd is euthanized in most cases.
Palmer and his colleagues are working to develop a better test which will allow producers to identify and remove infected cattle and keep TB-free animals. They are investigating antigens, which are components of foreign bacteria or viruses within the body that cause the immune system to produce a response.
Veterinary medical officers Ray Waters (left) and Mitch Palmer prepare to collect blood to be used in developing improved tests for tuberculosis in cattle. Their research is already paying off. A new serum TB diagnostic test was recently developed by IDEXX Laboratories, Inc., in Westbrook, Maine, based on NADC scientists' findings that an antigen called MPB83 is useful in bovine TB antibody-based tests.
"This was a team effort," says NADC veterinary medical officer Ray Waters. "IDEXX used samples from our experimental infection trials, and we helped the company validate and optimize the test and assisted with worldwide field analyses with colleagues in the United Kingdom, New Zealand and Ireland to verify the test's sensitivity and specificity."