“It doesn’t make animals sick directly,” he told Auckland Federated Farmers executive.
“It’s more like a cold sore where something happens to an animal which is weak already and M bovis jumps in and makes it worse.”
Genetic analysis showed the local strain of M bovis is quite different to that seen in Australia for the last 10 years.
“It’s similar to North American and European strains and has some similarity with those from Asia,” he said.
“It seems certain it arrived on only one farm.”
There are seven ways it could have arrived, all of which are improbable.
Live cattle imports constitute the highest risk but there have been none for the last four years and very few in the three years before that, he said.
Semen, embryos, contaminated machinery or clothing or biological medicines or vaccines and feed imports are the other ways.
“We’ve focused on semen because of the number of imports, which are larger than embryos,” he said.
“It seems certain it arrived at only one farm.
“But there’s a big risk of silent carriers, which will break into the disease.”
MPI is going through the last two years’ NAIT records from the 33 infected properties.
“There are a few holes where we will see the disease pop up again next season,” he said.
“It’s not just one group that has failed to make NAIT work.
“The whole system hasn’t been working as well as it could.”
Anomalies had not been followed up and enforcement action taken.
Auckland Federation vice-president Alan Coles is concerned that because some farmers are not filling out their records correctly, all farmers might face more bureaucracy as a result of the recent review of the system.
And Edgar Henson, who owns a sheep and beef property at Glen Murray, was worried about lost NAIT tags, particularly if that animal had been bought in.
NAIT advice when that happened with one of his animals on a truck recently was that his file could be dumped and then his stock rescanned.
“It’s a big weakness,” he said.
Murphy said there is a problem with missing tags if animals are not going to slaughter.
“Who do you call when tags fall out?” he asked.
When information had been entered correctly the system worked well but there could be issues if it is impractical to tag an animal or when a person receiving stock doesn’t acknowledge that has happened.
The 33 infected farms were “in context, not a great number”, he said.
Those with the disease in South Canterbury were not necessarily where it started but more likely to be a branch from an initial infection that started in Southland.
“It’s not moving very quickly from animal to animal and there’s been no transmission in NZ across a boundary fence,” he said.
It could be spread by semen, saliva and milk with 75% of the spread coming from animal to animal contact and up to 10% spread by feeding raw milk to calves.
Theoretically it could be spread by urine and manure, by clothing and on vehicles but that was not the core mode of transport.
“It doesn’t last that long and is mainly killed off by drying out,” he said.
“It can be very short-lived.”
On pasture a 60-day period of fallow is enough to kill it but where cows are housed viable organisms can survive longer in bedding and on rubber matting.
