Vaccine hunt a priority if M. bovis sets in

If the cattle disease Mycoplasma bovis becomes established, research to find an effective vaccine for the New Zealand strain would become a priority, says the Ministry for Primary Industries.

In response to inquiries about science and testing improvement initiatives in the wake of the government-agriculture sector decision to keep trying to eradicate the disease through a mass cattle kill, MPI said there was no suitably effective vaccine available globally.

This was due to several complex reasons which meant vaccination was unlikely to become a useful tool in the eradication campaign.

“However, if the disease was to establish, then research into producing an effective vaccine for the New Zealand strain over the medium to long term would be a priority,” MPI said.

Vaccines were licensed for use against M.bovis in some countries but had not demonstrated guaranteed immunity or protected an animal from getting sick, MPI said.

The reasons research groups around the world had failed to develop a vaccine included the lack of complete understanding about the immune response to M. bovis, the bacterium’s ability to hide from the immune system and because M. bovis often caused disease in partnership with viruses and other bacteria.

The world-first attempt to try to eradicate the disease, which was first diagnosed on two South Island farms in July last year, will mean about 126,000 dairy and beef cattle will need to be killed. That’s in addition to the cull of 26,000 cattle already under way or completed.

MPI has said this action was necessary because the disease was very difficult to test for and couldn’t be reliably identified at an individual animal level. Healthy animals could still carry the infection and infect others.

Asked what MPI was doing to find a more reliable new test, MPI said it was “paving the way” in best utilising two existing tests to detect latentlyinfected herds, which had not been done overseas.

The two tests are the PCR DNAbased test and the ELISA test.

A new improved ELISA test developed overseas was better at detecting positive animals but was not yet commercially available. However, MPI’s laboratory would receive test kits soon to start validating the test for use in New Zealand. The PCR test was good at detecting M. bovis if it was present in a sample, but infected animals only shed the bacterium intermittently and often there was no bacteria in a sample. This resulted in false negative test results.

The ELISA test detected antibodies in blood or milk, which was part of the animal’s immune response to infection. This test also commonly gave false negative results.

Strains of M. bovis overseas were showing increasing resistance to antibiotics. The New Zealand strain was not one of the super-resistant strains, the ministry said.