Faster Bovine Tuberculosis Test May Curb Cattle Infection

By Ruth Hall

Bovine tuberculosis (bTB) is a major economic concern in many regions of the world, particularly in Europe and some U.S. states. Because it is incurable in cattle, the need for efficient tests is paramount.

"Bovine TB is a growing concern in the U.S. as we are starting to have more states with infected cattle," says James Averill, coordinator of the Michigan Bovine TB Eradication Program. To stem disease spread while not overburdening the industry, "we need faster diagnostics."

Now, a faster test for bTB that could stem the spread of infection recently entered trials for commercialization and offers a new avenue for diagnosis of this incurable and costly disease. This antibody test, developed by William Davis at Washington State University College of Veterinary Medicine with scientists at Enfer Scientific in Ireland, can identify an infected animal in a single day, whereas current tests for bTB require days to weeks to complete.

The test is "showing potential," says Averill of Enfer Scientific's bTB test.

Because no treatment for bTB currently exists, infected animals must be culled from the herd. The longer an infected animal lives in the herd, the greater the chance it will spread bTB to other animals, increasing the chance of revenue loss. The U.S. began a bTB eradication campaign in 1917 that wiped the disease from the country for a limited time by killing all infected and exposed cattle. Due to economic realities, "we're at a point now where we can't kill a whole herd for one animal infected with bTB," says Davis.

Bovine TB poses a particular risk to the economies of states like Michigan that have infected herds with just a small percentage of infected cattle, says Averill. Because states without bTB do not want to risk introduction of infection, they often refuse sale of cattle from certain areas known to have even a few confirmed bTB cases.

Unlike Michigan, Washington state does not have endemic bTB disease, according to Jack Field, executive vice president of the Washington Cattlemen's Association. Since bTB has not been found in beef cattle in Washington, "it allows for freer movement and keeps the costs down," says Field.

Faster testing could benefit states like Washington because periodic bTB testing is required to confirm bTB-free status.

Enfer Scientific's antibody test was created by identifying a panel of Mycobacterium proteins, called antigens, which are typically produced during infection. Davis explains that this test uses up to 25 antigens to identify an infection and can be completed in several hours at a centralized lab. Current tests for bTB use a single antigen or require culturing of bacteria which takes a few days or more to complete, he explains. Also, using multiple antigens allows the test to identify bTB at multiple stages of infection, increasing the specificity and sensitivity of testing.

Enfer Scientific is currently seeking the European Union's approval to license their test in all of Europe, which includes the countries with the highest incidence of bTB, says John Clarke, Enfer's technical manager. Davis hopes the test will eventually be licensed in the U.S. as well.

Ruth Hall is a Ph.D. candidate in the Department of Microbiology at the University of Washington.

Images

Top: Cows cannot effectively be treated for bovine tuberculosis, so a faster diagnosis may keep infection from spreading through herds.

Photo: USDA Natural Resources Conservation Service

Bottom: William Davis, professor at Washington State University, helped design a faster tuberculosis test for cattle. Photo: Washington State University Center for Reproductive Biology