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Researchers explore rapid diagnostic test for bovine TB

Progressive Cattle Editor Carrie Veselka Published on 24 October 2019
Calves

Bovine tuberculosis (bTB) is difficult to detect in its early stages and can be highly contagious. A case of bTB in the U.S. will result in the culling of the infected animal and possibly more of the herd if the disease has spread.

According to the USDA, the main method of testing is a tuberculin skin test, where the animal receives an injection of tuberculin in the skin and is checked for a reaction 72 hours later. There is also a nationwide surveillance program in slaughter plants. If lesions consistent with bTB appear on a carcass, a sample is sent to the USDA’s National Veterinary Services Laboratories for confirmation. Random sampling is also performed. More than 1 million animals receive the skin test, and the USDA reports upward of 11,000 cattle are sampled in the slaughter plants each year.

Administering and processing the tests can be costly and time-consuming for the producer. In order to avoid culling an infected herd, a faster, cost-effective test that detects active bTB disease is needed. Dr. Wondwossen Gebreyes is a professor of veterinary medicine and executive director of the Global One Health initiative at Ohio State University. “(Global One Health) looks at different issues and how they impact human health, animal health and the environment, and we look at different capacity-building possibilities and do research,” he explains. One of these issues is tuberculosis (TB) and the diagnostic need in developing regions.

A multidisciplinary team of researchers – doctors, scientists and veterinarians with the Global One Health initiative – joined up to explore the possibilities of adapting rapid diagnostic TB tests primarily used for diagnosing human TB in third-world countries for use in cattle. “I learned that there is a rapid diagnostic test available for humans, and I asked the question, ‘Have we modified this test for Mycobacterium bovis?’ Our team modified that test. We wanted to do both. We wanted to find out if the modified test would work – not just work, but how specific the test would be for M. bovis.

Dr. Shu-Hua Wang, a professor of medicine at Ohio State University, medical director of the Ben Franklin TB Program at Columbus Public Health and the state TB consultant for the Ohio Department of Health, is one of the leads on the project. “It was the natural idea to bring in more than one health approach with human/animal interface, so we brought in veterinarians, brought in basic scientists, statisticians and microbiologists to come up with tests to improve the diagnosis of TB. We were working on coming up with point-of-care testing, where we can have a diagnostic test we can use right on the spot to make a diagnosis.”

The experiment

The team first conducted experiments in the laboratory to test different methods to improve sensitivity of the test in urine and milk. Then the team tested cattle herds in northern Michigan in areas where an outbreak was occurring. They also conducted a community outreach and education event about bTB and worked with the Michigan Department of Agriculture and Rural Development to collect some urine and milk specimens from known infected herds to test whether or not a test meant for human use would work for cattle. They also tested several herds outside Mexico City, Mexico and Ethiopia.

The rapid diagnostic test delivers a result within 25 minutes as to whether or not the subject is infected with the M. tuberculosis complex disease. “This reveals a common form of human TB, M. tuberculosis, and the zoonotic TB M. bovis,” Wang says. “Both of these are part of the M. tuberculosis complex, so the test would work for both.”

The first batch was tested from a group of already diagnosed, quarantined cows at a slaughterhouse. The test worked, but it is too early to determine absolutely if the test would be accurate in every case. “As we do more research, there are different species, different strains, and every single animal is different.” Wang says the logistics of collecting samples in Michigan and taking them back to Ohio to be tested, along with every animal not receiving the same round of tests, makes it challenging to compare and to get clear data. “We need to implement the study in developing countries and to compare the rapid diagnostic tests with other tests including gold-standard culture tests.”

Global perspective

The process for handling a bTB outbreak in the U.S. is to quarantine and test the herd, and slaughter infected animals if necessary. Wang says that, on a global scale, many of the countries which struggle with bTB do not have a surveillance, prevention and control program, and the producer and community often don’t have the capacity to screen for bTB, let alone depopulate their herds. Another challenge for less-developed countries is the widespread consumption of contaminated animal products like unpasteurized milk, or raw or improperly cooked meat from an infected animal that can still be dangerous.

Rapid benefits

A twofold benefit of using quick-turnaround testing is: Producers or consumers can take immediate action, i.e., boil the milk or dispose of the animal. “We would think that having a test like this would prevent an outbreak in advance because it allows early rapid detection, so if there are a few cases already known, with early detection you can prevent an outbreak or, if there is already an outbreak, it can be quickly contained,” says Gebreyes.

Another benefit is: The test is easy to administer and does not require a lot of laboratory equipment or time at a lab, making it both a timely and a cost-effective solution.

Next step

Gebreyes says the next step in the research is to improve the test’s sensitivity and specificity of which strain the subject is infected with. Once the test is more accurate, the next step will be finding a way to produce it in bulk. “How can it be produced en masse with a reasonable cost, partnering with a private industry group, and how can we make [it] available will be the next questions,” he says. “But before we do that, our main goal now is still at an early stage, so we see the next step as improving the diagnostic ability of the test.”

Wang says that working together with people from several different backgrounds and areas of expertise is critical to finding solutions to issues like bTB. “It takes multiple sectors to all come together. We can’t be siloed and just working in our own field because [Global One Health] is a multidisciplinary work that needs to take place in order for us to improve human and animal health.”  end mark

PHOTO: Animals infected with M. bovis may not show any outward signs of the disease until the most advanced stages. Photo by David Cooper.

Carrie Veselka
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