A faster way to detect TB in cows

A new inexpensive test can detect the bacterium (Mycobacterium bovis) that causes bovine tuberculosis (bTB) in cattle.

“This test delivers results within 48 hours and the frequency in which viable mycobacteria were detected in the blood of skin test positive animals changes the paradigm of this disease,” says Cath Rees, an expert in microbiology at the University of Nottingham who led the team.

The UK has struggled to eradicate bTB and control measures continue to be a significant economic burden on the agricultural industry. Most cattle are regularly monitored for signs of infection with a skin test, but it’s not effective enough to identify all infected animals.

“The data we are getting has taken the scientific community by surprise. In our paper we show that when blood samples from skin test negative cattle were tested for M. bovis cells, all the samples proved negative,” says Rees. “However using just a 2 ml blood sample, viable Mycobacterium tuberculosis complex bacteria (MTC) were detected in 66 percent of samples from skin test positive animals.

“When the carcasses were inspected, it was found that the highest number of bacteria were detected in the animals with visible TB lesions (VL) and 85 percent of these VL animals were M. bovis positive.”

Difficulties in detecting, growing cultures, and achieving sensitive detection using the current skin test, which looks for the animal’s an immune response, are a major barrier to understanding and diagnosing bTB infection. Early results indicate that M. bovis can be detected before the animal becomes SCCIT-positive.

“Using our bacteriophage-based test, the hope is that we can help improve herd control by finding animals at the early stages of infection and helping farmers control outbreaks of bTB more rapidly,” says Rees.

The group has patented an improved version of the method that delivers more sensitive results in just six hours.

Working with the US Department of Agriculture, Agricultural Research Service, National Animal Disease Center, the Nottingham group has set up the first animal trial using the blood test to determine exactly how soon it can detect infection.

“The test also offers the potential for new, better tests for other farm animals. We are directly detecting the bacteria and so the method will work using blood samples from any animal species—so far we have detected mycobacteria in the blood of cattle, sheep, and horses, but it could also be used for deer, goats, or llamas.

“Not only that, we can detect any type of mycobacteria, we have use the same method to detect other diseases, such as Johne’s disease, not just bTB.”

The team describes results in a paper published in the journal Virulence.