New Tb test for deer could mean huge savings

Media release

24 May 2007

Development of new Tb test for deer could mean huge potential savings for agriculture industry

The current Tb skin test is estimated to cost the New Zealand deer industry alone over $300,000 a year in false positives.

The Animal Health Board (AHB), with the help of AgResearch Invermay veterinary scientist, Dr Colin Mackintosh, has taken the first step in the process of investigating whether there may be a better way for testing deer for Tb.

Dr Mackintosh, who is trialling new ways to improve the Tb skin test, said if a more accurate and economical test was developed it could mean huge savings for the industry. But it will take time and he urged farmers not to be over optimistic of the outcomes.

Dr Mackintosh said of those animals that currently test positive under the most commonly used method, the mid-cervical intradermal test, 99% will be false positives.

“Of the half a million deer tested annually for Tb, about 5000, or 1%, react to the test. Of those that react, around 50, or 1%, actually have bovine Tb,” said Dr Mackintosh.

“The national Tb eradication programme has successfully reduced the occurrence of Tb in New Zealand. But even though there are fewer and fewer cases of diagnosed Tb, the number of deer testing false positive for the disease is increasing.”

False positives usually occur when the animal has Johne’s disease, a member of the same bacterial family as Tb. The trials Dr Mackintosh and his team are conducting are designed to make the bovine tuberculin used in the skin test more specific for bovine Tb and less cross-reactive with other mycobacteria.

According to Dr Mackintosh, whether the result is accurate or not, the farmer has lost money as soon as an animal tests positive for TB.

Once this happens, the farmer is left with three options:

- Kill the animal on the farm and employ a vet to inspect it for Tb.

- Send the animal to the slaughter plant where, if it passes meat inspection, it will be sold only for local consumption at half the value of international consumption, or,

- Re-test the animal using a different method.

Retesting the animal has numerous hidden costs including time delays, quarantining the animal before retesting and the risks of the test resulting in a false negative or another false positive, depending on the method used.

“If our trials result in a successful new Tb test it would mean we could reduce the amount of false positives for those testing on properties with Johne’s disease,” said Dr Mackintosh.

“Farmers then wouldn’t have to retain so many animals for retesting and the AHB would be able to control Tb without the extra costs of dealing with Johne’s disease.

“Ultimately it could mean huge savings to the farmer and, as a consequence, the industry but we’re a long way off that yet.”

Dr Mackintosh is presenting at the New Zealand Veterinary Association Large Animal Conference which is being held this week in Palmerston North.

ENDS

The New Zealand Veterinary Association Large Animal Conference is being held at the Palmerston North Convention Centre, 400 Main Street West from 23 – 25 May.

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