3 March 2000

TB test comes under scrutiny as cases missed

AN investigation into the accuracy of the tuberculin test for TB in cattle estimates that 38 breakdowns may have gone undetected in 1998.

The TB Independent Scientific Groups report, published in the Vet Record, expresses concern that the tuberculin test accuracy is limiting disease control in parts of the UK where the disease has persisted.

While the tuberculin test identifies 99% of uninfected animals correctly, one in 10 infected animals can be missed by the test in single reactor herds. This amounts to 38 missed breakdowns in 1998, says the report.

But as the number of reactors in a herd increases, the likelihood of reactor animals remaining undetected increases, warns the report. This may be prolonging multiple reactor breakdown incidents.

The report also says that because a positive test is based on measuring small differences in skin thickness, reading of the test is subject to error.

But the Independent Scientific Group is hopeful that a new TB lab test which will ensure all infected animals are detected may be developed for follow-up screening in breakdown herds. &#42