New test could allow earlier TB detection

Researchers at the University of Nottingham in England have developed a blood test that can quickly detect Mycobacterium tuberculosis complex bacteria (MTC) in cattle. The test, according to the researchers, can detect the bacterium Mycobacterium bovis faster and earlier than the currently used Single Intradermal Comparative Cervical Tuberculin (SICCT) skin test, which is about 90% sensitive.

The research team, led by Cath Rees, a microbiologist at the university's School of Biosciences and Ben Swift from the School of Veterinary Medicine and Science, published their results in an article titled "Evidence of Mycobacterium tuberculosis complex bacteraemia in intradermal skin test positive cattle detected using phage-RPA," in the journal Virulence.

The researchers adapted a bacteriophage-based method combined with PCR (phage-PCR) and using a new isothermal DNA amplification protocol using Recombinase Polymerase Amplification (RPA) to detect and identify viable pathogenic mycobacteria in the peripheral blood mononuclear cells (PBMCs) of animals suffering from paratuberculosis.

In this study, the scientists tested 2 ml blood samples from a SCCIT-positive herd of 45 cattle, and the tests were all negative for MTC cells. They also tested blood samples from 41 SCCIT-positive animals, and detected viable MTC cells in 66%. Within that group, 13, or 32%, had visible lesions. Among that group, 85% had detectable levels of MTC. Among the remainder, with no visible lesions, 57% were found to have detectable mycobacteraemia.

The researchers conclude that their results indicate a simple, rapid method can be applied for the study of

M. bovis

infections, and "the frequency with which viable mycobacteria were detected in the peripheral blood of SCCIT-positive animals changes the paradigm of this disease." In a news release, they also suggest the method could be used to detect other types of mycobacteria, such as that causing Johne's disease in cattle.