About the mycoplasma bovis bug in Aus that NZ will kill 150,000 cows to erase

The NZ government announced yesterday that it will cull another 126,000 cows in addition to the 26,000 already slaughtered in an attempt to rid the country of mycoplasma bovis.

The massive cull has already led to heartbreak for Kiwi farmers but NZ’s peak farming body says the anguish is worth it.

“Federated Farmers believes getting rid of this insidious disease is preferable to living with it, for years on end, probably without any compensation available for farmers in future when it does hit and can’t be controlled,” NZ Federated Farmers wrote in a statement.

The bug has been in Australian herds for decades so I’m really grateful to veterinarian Dr Zoe Vogels for her explanation of the M. bovis basics. Thanks Dr Zoe!

MMM: What is Mycoplasma bovis?
ZV: Mycoplasma bovis is a bacteria that likes to live inside cows – generally in the respiratory system and the udder and joints. Infected cows will shed bacteria from mucous membranes and in their milk. It grows slowly and likes special conditions in the lab so can be difficult to diagnose. You might have heard about the bulk milk PCR test: this looks for the DNA of Mycoplasma rather than trying to grow it.

MMM: How common is it in Australia?
Mycoplasma’s not super common, but every dairying district would have farms that have had it diagnosed – either at present or in the past.

MMM: How do animals get it?
Cows are generally infected during milking time via infected milk on hands, gloves, milking equipment or antibiotic tubes. Where animals have pneumonia and respiratory shedding, close contact/poor air quality will play a role in spread.Calves seem to be most often infected by being fed waste milk that has mycoplasma in it from mastitis cows, but the respiratory spread will also occur.

MMM: What are the symptoms?
The signs present differently in different situations, in cows the most common symptoms we’ve seen are mastitis (often multi quarter and non-curing and won’t grow anything on normal lab culture) and swollen joints/limbs. Sometimes cows can have pneumonia or ear infections, some countries report abortions.In calves we generally see joint infections (in multiple joints) and sometimes pneumonia and ear infections.

MMM: Is it treatable?
Unfortunately, Mycoplasma doesn’t respond well to antibiotics. Antibiotics such as penicillin work by stopping the formation of a bacteria cell wall during their growth phase and Mycoplasma doesn’t have a cell wall, only a thin surrounding membrane.

how antibiotics work cartoon ZV.jpg

There are some antibiotics that are more likely to be effective, but these don’t always work. Mycoplasma is also able to evade the immune system by camouflaging itself from white blood cells and antibiotics and can form biofilms which also protect it from the immune system and antibiotics.

MMM: What should I do if it affects my farm?
ZV: In the words of the Hitchhikers Guide to the Galaxy, don’t panic!
Sit down with your vet, make sure you get your head around how the disease spreads and set out a plan of action. It is important to work out how prevalent it is in your herd, generally through culturing of clinical mastitis cases.

While you are working this out, you will have to plan how to minimise chance of transmission between cows during milking time (such as rapid detection and segregation of clinical cases). These are the same principles that apply to minimising the spread of other mastitis pathogens such as Staph aureus and Strep ag.

You will also have to minimise the risk of transmission to calves by feeding the lowest risk source of milk, such as milk replacer or pasteurised milk. What option you choose will depend on your own farm’s circumstances.

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