Scientists at the USDA's National Animal Disease Center in Ames, Iowa, are working to develop new techniques that expand on old ones in effort to better control tuberculosis in cattle populations.
Ray Waters and Mitch Palmer, veterinary medical officers, 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.
New tests expands on traditional methods
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 more effective serum tests. These findings were instrumental in the recent development of a new serum TB test by IDEXX Laboratories, Inc., of Westbrook, Maine.
The test has been added to the World Organization for Animal Health registry and licensed by USDA's Center for Veterinary Biologics.
Thacker has developed another type of test, based on polymerase chain reaction analysis of DNA. 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.
The newly developed assay was tested against 11 mycobacterial species commonly cultured from diagnostic samples. Specificity for detecting M. bovis was 100% and sensitivity was 67% in samples from 30 infected and 18 uninfected animals.
"The specificity of the new PCR is the most important result," Thacker says. "The fact that it's quicker than a traditional PCR is an added benefit."
Read more about the expanded TB research here.