Mass testing of milk from all dairy farms this spring has so far turned up only three properties with the cattle disease Mycoplasma bovis.
The testing has been carried out over the last 12 weeks, starting at the top of the North Island, and is nearly finished in the South Island.
Ministry for Primary Industries principal scientist Dr John Roche conceded that several months ago there were some doubters within MPI and elsewhere over the possibility of eradication.
“If you went back a couple of months before we started the spring milk testing, there were a number of people who were concerned we would learn stuff this spring that would make us change our minds.
“Even those of us confident we could eradicate it expected to see a greater outbreak. But now you won’t find too many dissenting views,” Roche said.
Part of the reason why so few cases were being detected was the time between infection and identification had become so short that animals were not spreading beyond infected farms.
Roche said he was personally committed to eradication after his experience in the United States a decade ago when he was working on a dairy farm with the disease.
“I wouldn’t wish it on my worst enemy. Nationally we could manage it but on individual farms it would be an unmitigated disaster. We set up a couple of farms in the US just over a decade ago and brought different herds together as we created our own herd, but ended up in an incredibly stressful situation. Within weeks of calving we were dealing with uncontrollable mastitis and calves dying.”
Roche also wanted to address several myths surrounding the disease. These included:
* M bovis first arrived in New Zealand around 2004;
* Intensive barn farming has aided the spread of the disease.
Roche said scientists were confident M bovis was a recent arrival, despite persistent claims it has been in New Zealand for more than a decade.
Two threads of evidence support the official narrative. One is a bulk milk sampling across the country carried out in 2007 which failed to detect the disease, the other recent DNA testing of the bacteria.
In 2007 scientists and officials from the former Ministry of Agriculture random-tested the milk of 244 herds for the presence of the disease, but detected nothing.
Roche said the other evidence related to the DNA testing of the bacteria.
“We’re using a molecular clock, the bacteria mutates every so often so by culturing the bacteria and sequencing the genome we can see the changes in the DNA of the bacteria through time and that gives us great confidence.
“Massey’s epidemiology team are confident on the basis of all the samples they have, that it started here between December 2015 and January 2016, and the more samples we analyse the narrower the window,” Roche said.
However commentator Keith Woodford has raised the possibility of other cases “where the logical infection path only makes sense if the disease were here by 2014 or earlier”.
An MPI spokeswoman said MPI had invited Woodford on several occasions to provide evidence to back up his claims but he declined to do so. He also did not have the same detail of information that MPI had.
Roche said there was no international scientific evidence that M bovis survived in soil. The primary risk pathways were cattle-to-cattle contact or contaminated milk.
He refuted claims intensive barn farming aided the spread of the disease.
Most of the cattle detected in New Zealand had been grazing outdoors for most of their life. The disease might spread through a farm “a bit quicker” if cattle were in intensive systems.
The latest figures show there are 33 infected properties, restricted properties stand at 53, and those under notices of direction are 248.
There are 277 under active surveillance, referring to properties which MPI have identified are at risk and testing has begun to confirm whether the disease is present or not.