New TB test shows encouraging signs

Principal scientist Professor Bryce Buddle says it is early days yet, but they have encouraging preliminary results from a trial which shows the potential for a more accurate and cost-effective diagnostic test in the battle against bovine TB.

“The current test used on New Zealand farms often gives false positives, and a blood test is needed to confirm infection. We have developed a new skin test that has a similar sensitivity to the existing reagent bovine tuberculin, and fewer false positive reactions in non-infected animals,” he says.

Buddle and colleagues at the Hopkirk Research Institute in Palmerston North have shown that by displaying three or four specific M. bovis proteins on the surface of polyester beads (bionanoparticles) — a cost-effective and more reliable skin test reagent for bovine TB can be produced.  

The original beads technology, known as Biobeads, was developed by Professor Bernd Rehm at Massey University. Professor Rehm is the chief science officer at the NZ biotechnology company PolyBatics Ltd, the company that now owns the technology and is developing products.

Buddle says the advantage of this approach is that the proteins have stronger immune responses when displayed on very small particles and can be used in a very low concentration; in addition, the Biobeads can be produced at low cost using fermentation technology.

“This new reagent has the potential to be used in a TB diagnostic blood test as well as the human skin test for tuberculosis,” he says.

A large field trial is now underway to estimate the sensitivity and specificity of the test compared with the existing bovine tuberculin.

Already at least 30,000 cattle and 3000 deer have been tested, yielding encouraging results for specificity and significantly fewer false positives than for bovine tuberculin; the test is on track to deliver equivalent sensitivity.

Buddle says the new skin test reagent has attracted international attention and material has been supplied to the US Department of Agriculture and the UK Department for Environment, Food and Rural Affairs for testing of the reagent for TB diagnosis in cattle.

This work is funded by the Ministry of Business, Innovation and Employment as part of a five-year contract and PolyBatics Ltd is commercialising the new reagent.

Scourge of animals, humans

Bovine TB is a chronic disease of animals caused by bacterium called Mycobacterium bovis (M. bovis), which is closely related to the bacteria that cause human and avian tuberculosis. Bovine TB can affect most mammals, causing illness, coughing and eventual death. 

The disease is contagious and spread by contact with infected domestic and wild animals. 

While the incidence of bovine TB has been greatly reduced in the developed world, significant pockets of infection remain in wildlife in NZ, UK and to a lesser extent the US and Canada, putting at risk livestock there.