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M bovis: A 'tricky disease' that's 'not easy to tame'

By Dr Helen Beattie*

Opinion - As a veterinarian working on the foot and mouth response in the UK, I've seen the misery that outbreaks of serious infectious diseases can bring down on the agricultural sector - animals, farmers and their communities. Containing these outbreaks always involves hard choices and significant consequences - there are seldom any easy solutions.

Photo: RNZ / Rebekah Parsons-King

So, I don't envy the government ministers who will make the call on how New Zealand will respond to the Mycoplasma bovis (M bovis) outbreak. They have to choose between trying to eradicate the disease or accepting that it has taken hold in New Zealand and opting to manage it.

M bovis is a tricky disease and whatever option is chosen, it will not be easy to tame. Which ever way the decision goes, there will be no going back to business-as-usual on farms.

M bovis is a bacterium that causes a variety of illnesses in cattle, including mastitis (udder infections), pneumonia and arthritis. Ministry for Primary Industries information tells us it does not infect humans and so presents no food safety risk. I would happily eat the meat and drink the pasteurised (for other food safety issues, not M bovis!) milk from an M bovis infected cattle.

From a veterinarian's point of view, eradicating this disease is the best solution. It is by far the best outcome from an animal welfare point of view. Long-term, it would also be best for farmer wellbeing and for minimising antimicrobial use on farms, which has implications for preventing antibiotic resistance.

But eradication would come at a cost. It would require widespread culling of animals identified as positive and would constrain stock movements, which could have serious animal welfare implications. This is currently playing out, with significant numbers of stock unable to get to winter feeding locations.

Eradication would be extremely stressful for farmers - financially and personally. And it could take years to achieve because infected animals might have no signs of illness and the bacterium is hard to identify through testing. These two issues make it very difficult to contain. Eradication would also require a huge investment of capacity and resources by industry and government.

This (relatively) short-term pain might be worth it long-term if we could be confident of succeeding in eliminating the disease and maintaining our M bovis-free status in future.

Scientifically, this is possible. But there is growing pessimism that it might be too late - that the disease already has such a hold that it can't be reined in.

Currently, and rightly so, M bovis is being treated like a 'tiger', with every weapon we have being used to try to subdue it including legal notices and controls on stock movements.

However, the 'good' news is that other countries manage to live with this disease without their industries being devastated - in fact, it exists in all other cattle and dairy producing countries. Although M bovis will have some scratchy parts from time to time (i.e. clinically sick animals), it can be tamed given appropriate herd management. We need to be mindful of this - the tiger-y-ness won't last forever.

The 'bad' news is that managing it is difficult because M bovis is hard to see, hard to test for, and hard to treat. You don't always see clinical signs, or if seen, they can look like other diseases. Testing is tricky and the results are inconclusive. Antibiotics aren't very effective in treatment of the disease. Culling infected animals is generally the only option.

Three key factors in M bovis management

With that in mind, if New Zealand goes down the management path we are going to need to educate farmers (and those on life-style blocks with cattle) about three key things.

First, they need to understand the best way of preventing the disease from spreading, namely through excellent biosecurity on farms. Biosecurity covers things like making sure new stock or stock movements don't bring the disease onto farms, using quarantine and ensuring it's not spread by feeding infected milk to calves. This outbreak is a stark reminder of why good biosecurity is so important for disease control.

Farmers need to understand how the environment in which animals live can increase the risks of disease - this includes herd management practices. They also need to understand what hygiene practices will and won't work. For example, spraying mud with disinfectant is a waste of time as it won't work.

Second, farmers need to understand how to identify and respond to the disease. Even for veterinarians, M bovis can be hard to diagnose because the clinical signs can be confused with other diseases and testing is inconclusive. Many variables need to be lined up to get an accurate test result and this is not always easy to do.

Given those constraints, it is necessary to consider the farm's likely level of risk regarding M bovis. This might involve considering the general health of the herd, including non-responsiveness to treatment of mastitis or arthritis. Guidelines will be required for veterinarians and farmers on how best to assess risk and on the best use of testing.

That takes us to the third key thing. Crucial to us being able to control the disease and respond appropriately is the National Animal Identification and Tracing scheme (NAIT). Under this scheme, individual cattle are tagged so their movements can be traced - including in the event of a disease outbreak.

Currently, use of NAIT is voluntary and patchy. Without a doubt, this severely hampered MPI's ability to respond to the current M bovis outbreak. Accurate NAIT records and the capacity to use this information to trace infected premises is critical. If we want to move to an environment where incursions, including of M bovis, are managed effectively, use of NAIT has to change.

Cabinet has a hard choice to make. It has to weigh up a range of evidence and perspectives from the industry, MPI and the veterinary profession.

Whatever decision Cabinet makes will only be seen, in the future, to have been the right one if it is supported with an holistic action plan. This plan needs to take into account the scientific evidence, feasibility and the welfare of animals and people.

Taming the M bovis tiger will not be easy. But it can be done.

* Dr Helen Beattie, chief veterinary officer, New Zealand Veterinary Association. NZVA is the membership association for New Zealand veterinarians.

© Scoop Media

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