29 Mar 2018

Scientists more pessimistic about eradicating cow disease

6:10 am on 29 March 2018

A long awaited report into mycoplasma bovis has provided no definite answers on how the disease got here and whether it can be eradicated.

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Photo: RNZ / Rebekah Parsons-King

A cull of 22,000 cows began this week, and the ministry raided three properties as it continues to investigate how the bacteria arrived here.

In its latest report, the Ministry for Primary Industries' technical advisory group said it was still feasible and desirable to eradicate the disease but the task was bigger than first thought and some members of the group were more pessimistic.

They say there is uncertainty about the cost and effectiveness of efforts to control mycoplasma bovis, and believe success is unlikely.

The disease may have spread undetected from as early as 2015 and the system used to track animals, whether infected or not, has failed, the report said.

For the report scientists looked at seven potential routes of entry - including imported live cattle, frozen semen and embryos, veterinary medicines, and biological products.

While the report reaches no conclusions that any of these are to blame, it does put the risk of imported semen and embryos higher than other pathways.

It recommends that more research needs to be done on imported genetic material, and also says imported live cattle should be located and surveyed.

The group suggests further analysis of the economic impact on the dairy sector was required to establish whether attempts to eradicate are even worth it.

The technical group is meeting in the next few weeks to discuss what the next steps for the outbreak should be.

What we know about the disease

  • Mycoplasma bovis was first identified in New Zealand on 22 July, 2017 after sick cattle were reported at one of the Van Leeuwen Dairy Group farms.
  • The disease causes mastitis, pneumonia, abortions and lameness, and can result in the deaths of cows and calves.
  • The disease can be hard to detect and treat because it has special characteristics including: The lack of a cell wall so that certain widely-used antibiotics are not effective; an ability to hide away from the immune system so that infections are difficult for cows to fight; the ability to create conditions that allow evasion from antibiotic treatment (eg within large abscesses).
  • Not all infected cows get sick or show signs of the disease, making it hard to detect. Some shed the disease without becoming ill, allowing for transmission between farms if these cows are moved.
  • It is mainly spread through 'nose to nose' contact between cattle through mucus and bodily fluids, and by direct contact between infected animals and equipment.
  • Mycoplasma bovis does not infect humans and presents no food safety risk. There is no concern about consuming milk, milk products, or meat.
  • While some of the conditions can be treated, affected cattle will always be carriers of the disease.
  • In Australia, the disease is throughout most dairying regions and had devastating impacts on some individual farms, leading to cows and calves being killed.
  • Since the disease arrived in Australia farmers have been using a PCR test, which detects evidence of infection in bulk milk.

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