Milk companies are this week taking bulk milk samples from tankers in the southern region of the North Island as national surveillance for Mycoplasma bovis moves into areas with no known infection.
Testing the tonsils for the bacteria is by no means easy – effectively it is only feasible at slaughter – but it is giving the most accurate results, says MPI response coordinator David Yard.
Yard explains that when the disease was first found here last July, New Zealand and Norway were the only two developed milk industry countries where Mycoplasma bovis was not already established.
Other countries had “just learned to live” with it.
That meant there had been a number of testing methodologies developed, but none was really applicable for what NZ wanted to use it for, he said.
“Because we are truly going for eradication we have to have confidence in the technology and the methodology of the testing.”
“So we’ve been experimenting with different methodologies, and we discovered that at slaughter we tried things like nasal swabbing and blood tests but by far the more accurate results we are getting at the moment are from examining the little crypts in the tonsils.”
As in humans and several other species, crypts are crevices, sometimes very deep, in the tonsils.
The bacteria “seem to like hanging out” in the crypts, says Yard.
However, he said getting to the tonsils is only practical at slaughter so it is not a standard methodology to analyse a whole herd.
“It’s only because we’ve been fortuitous and lot of these animals have been directed to slaughter that we’ve been able to look at these and discover that this is quite a good technique, or place to look, to find the bacteria.”
Yard said the discovery hadn’t yet made much difference in the way MPI is handling the disease, “but it’s helped us when we do send animals to slaughter”.
“We now know that we’ve got a target area we can go to which has given us more definitive results than the previous methodologies.”
Yard agreed that the discovery could potentially help in management if, in the worst-case scenario, Mycoplasma bovis cannot be eradicated.
He said blood tests can be non-specific because animals do not always raise antibodies against it.
“That’s why whenever we test a herd we are having to take between 100 and 130 samples.
“But if we have animals going to slaughter this is quite a good test to find out whether the herd is actually contaminated,” he said.
“It’s given us more confidence that we now have a test that we will be able to use for diagnosis to determine whether a herd is positive or not.”