New blood test for TB promises early disease detection

Scientists at the University of Nottingham have developed a new blood test for TB which has the potential to identify affected animals even at early stages of infection.

The researchers have developed a method which shows cattle diagnosed with bovine TB have detectable levels of the bacterium Mycobacterium bovis (M bovis) in their blood.

Early results point to the new test being able to pick up infection earlier than the traditional skin test which currently forms the basis of the UK’s cattle screening measures for TB.

See also: New TB rules hit cattle entries at shows

It is estimated that the Single Intradermal Comparative Cervical Tuberculin (SICCT) skin test used in the UK and Ireland also only detects about 80% of all the infected cattle in a herd at any one test.

Dr Cath Rees, an expert in microbiology in the School of Biosciences, said the data the team had generated had taken the scientific community by surprise.

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 help farmers control outbreaks of bovine TB more rapidly Dr Cath Rees, expert in microbiology

“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.

“However using just a 2ml blood sample, viable Mycobacterium tuberculosis complex bacteria (MTC) were detected in 66% 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% of these VL animals were M bovis positive.”

Following these findings, the team refined its methods, patenting an improved version of the test that is more sensitive and delivers results within six hours.

With this test, researchers found that all animals with visible lesions were MTC positive, and 26 out of 28 animals where the lesions were not yet visible were positive, suggesting that M bovis is commonly found in the circulating blood of infected animals.

Dr Rees said: “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 help farmers control outbreaks of bovine TB more rapidly.” 

The University of Nottingham is now working with partners in the United States to set up the first animal trial using the blood test, to detect M bovis in the blood of experimentally infected animals.

This will help to determine exactly how soon the test can detect infection.

Dr Rees said the test also offered 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 bovine TB.”