A new blood test to detect Mycobacteria in blood has been developed by a team at The University of Nottingham. The researchers have used this new method to show that cattle diagnosed with bovine tuberculosis (bTB) have detectable levels of the bacterium Mycobacterium bovis (M. bovis) in their blood which causes the disease, a major problem in the cattle industry.

The new blood test was developed by a team led by Dr Cath Rees, an expert in microbiology in the School of Biosciences, and Dr Ben Swift from the School of Veterinary Medicine and Science.
Dr Rees said, "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."

The researchers said the test is simple and inexpensive and can detect very low levels of mycobacteria in blood. The group has patented an improved version of a technique developed at the University of Nottingham that delivers results in just six hours. More recently 'proof of principal' experiments have shown that this is even more sensitive. This is currently licenced to a spin out company, PBD Biotech Ltd.

Despite a costly and - in some respects - controversial bovine TB control strategy, the UK government has struggled to wipe out the disease. New measures that came into force in April include tighter restrictions on cattle movement in the ‘high risk’ area designated by the government’s bovine TB strategy, free pre-sale TB testing and - in some circumstances - private gamma interferon blood tests, subject to the approval of Defra’s Animal and Plant Health Agency (APHA).

Routine testing for Bovine TB uses the Single Intradermal Comparative Cervical Tuberculin (SICCT) skin test for M. bovis infection and all healthy cattle are regularly tested this way. In the past, experts have been critical of the currently used skin test as, though it gives very few ‘false positives’ (incorrectly identifying healthy cattle as having bTB), its sensitivity is only around 80%, meaning it misses around 1 in 5 bovine TB-infected cattle.

Explaining her team’s results, Dr Cath Rees said, "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. However using just a 2ml blood sample, viable Mycobacterium tuberculosis complex bacteria (MTC) were detected in 66 per cent 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 per cent of these animals with visible lesions were M. bovis positive.

"More excitingly, using our new more sensitive six-hour method, this figure is even higher - all animals with visible lesions were MTC positive, and even 26 out of 28 animals where the lesions were not yet visible also were positive suggesting that M. bovis is commonly found in the circulating blood of infected animals."

Difficulties in detecting, growing cultures and achieving sensitive detection using the current skin test, which looks for the animal's immune response, are a major barrier to understanding and diagnosing bTB infection. Early results indicate that M. bovis can be detected before the animal would be detected using the skin test. 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 helping farmers control outbreaks of bTB more rapidly."

The Nottingham team is working with the US Department of Agriculture on the first animal trial of its test. Dr Rees said: "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."