Mid-Canterbury farms: M bovis eradication ‘not dependent on knowing transmission route’

8:39 pm on 6 February 2023
Cows grazing in Mid Canterbury where M bovis has infected five farms

An inquiry has failed to establish how Mycoplasma bovis reached some farms in Mid-Canterbury last year. Photo: LDR

The Ashburton mayor says it isn't a major concern officials are unsure how Mycoplasma bovis began circulating Wakanui farms in Mid-Canterbury last year because they continue to close in on eradication.

An independent expert review into M bovis infection in Wakanui has failed to produce a definitive explanation for transmission of the disease but programme director Simon Andrew said it showed appropriate steps were being taken to remove infection in the area.

The review was commissioned by the programme's partners, MPI, DairyNZ and Beef + Lamb New Zealand, in mid-2022 after it became apparent that infection was circulating in a small geographical area despite the use of disease control measures, which have proven successful in other areas around New Zealand.

Mayor Neil Brown said the report didn't provide a definitive answer on transmission but what it showed was appropriate actions were being taken to keep the eradication programme on track.

"I don't think it matters too much [how it was transmitted] as long as they identify the farms that have got it - which they have, and put a bigger buffer area in around it," Brown said.

"They are very close to eradication now, they are at the pointed end and have got it down to these last five properties."

The review was carried out by independent epidemiologist Dr John Happold and Andrew said while Happold didn't identify how it was transmitted he had endorsed the approach.

"While the review did not confirm the sources of infection in Wakanui, it notes that the area has been unique to other parts of New Zealand, which have experienced M bovis infection.

"Wakanui had a large, concentrated and dynamic population of infected animals within the local feedlot and there was a small cluster of confirmed properties, most of which have paddocks within 1.5km of the feedlot."

Ashburton Mayor Neil Brown.

Mayor Neil Brown says eradication is very close. Photo: Supplied

Transmission route may never be worked out

Dr Happold concluded the unusually high amount of infection on the Five Star Beef feedlot could have allowed for airborne transmission that was highly unlikely to have occurred in other areas.

"The review has not determined the transmission routes occurring in Wakanui with any certainty, and it is possible we may never be able to categorically say what the transmission route is," Andrew said.

"What we do know is, eradication is not dependent on knowing the transmission route.

"What is important is that we remove the infection from the area which is exactly what we're doing."

The report stated there was "good evidence" the feedlot was the source of infection for the farms in the current controlled area, but how it was transmitted was not so clear cut with the review unable to "establish with certainty the origin [or origins] of infection".

As part of the review, Dr Happold also looked at a range of transmission routes including mechanical vectors such as birds and flies, manure, effluent, and groundwater.

Happold concluded infection was unlikely to have occurred via these routes.

The review supported the depopulation plan for Five Star Beef and the use of a Controlled Area Notice (CAN), and made several recommendations which Andrew said were being implemented.

The eradication effort continues to make good progress Andrew said, with the high-risk area of the CAN now free of cattle and the CAN was on track to be lifted in mid-March.

"It is expected all current confirmed properties are likely to be cleared within the first half of this year.

"While the job is far from over, we are as close to moving to the next phase of the eradication as we have ever been and the collective effort from farmers, industry and programme staff has helped us get to where we are today," Andrew said.

Economically Brown said the district hasn't taken a hit due to the government's compensation but it has had its impacts.

"Physically and emotionally the farmers affected have taken a hit," Brown said.

"It is not a nice process to be in. Farmers get connected with their stock and always do their best to look after them."

The M bovis Eradication Programme began in May 2018 and is jointly funded by the government (68 percent) and DairyNZ and Beef + Lamb New Zealand (32 percent).

Key numbers:

  • 5 current infected properties (279 since the start of the programme)
  • Just over 3 million tests have been completed
  • $234 million has been paid out in 2838 claims
  • 180,872 cows have been culled

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