NZ Farmer - M bovis 'low risk' to humans

Written by Gerard Hutching

The possibility of humans contracting Mycoplasma bovis from eating meat or drinking milk from infected cattle has been dismissed by officials and food safety experts as a "low risk".

The Ministry for Primary Industries (MPI) said the disease was not a food safety risk. Concerns have again been raised over the culling of 152,000 cattle and whether their meat or milk might threaten human health.

"There is no issue with eating beef or drinking milk from infected herds. This disease is in every other farming nation and people have been consuming products from cattle with Mycoplasma bovis for decades," MPI said.

It added that M.bovis did not survive pasteurisation, and since most New Zealand milk is pasteurised, it would exist only in raw milk.

New Zealanders may in fact already have eaten meat from cattle that has been infected by Mycoplasma, because the disease occurs in Australia, which exports beef across the Tasman.

Last year about 2.4 million cattle were killed, mostly for export. The 152,000 cull to eradicate Mycoplasma will happen over two or more years.

The Ministry of Health has carried out a study called Risk Assessment: Mycoplasma bovis and Human Health, based on a literature review.

It focused particularly on a 2004 paper written by United Kingdom specialists D.G. Pitcher and R.A.J. Nicholas, which looked at the possibility of animal mycoplasmas crossing into humans. There are more than 100 mycoplasmas, of which Mycoplasma bovis is just one.

The authors found there had been only two instances of people being infected with M.bovis. Animal mycoplasmas (not just M.bovis) had been found in humans whose immune systems were more often, though not always, compromised.

"While it is true that such patients are susceptible to a wide range of microbial infections, it is well established that patients with hypogammaglobulinaemia or who are receiving immunosuppressive drugs have a particular susceptibility to mycoplasma infections."

They noted the 1979 case of an American woman where M bovis was isolated in her throat. She was already suffering from bronchopneumonia and central nervous system abnormalities.  

Her only contact with cattle was that she had been exposed to cow manure during gardening three weeks before developing the symptoms. The disease subsided following tetracycline (an antibiotic) therapy.

In the other case of M.bovis infection, the Ministry of Health noted there were "scant" details and again the person had responded to tetracycline treatment.

Professor Nigel French, director of the New Zealand Food Safety Science & Research Centre at Massey University, said other diseases such as campylobacter and salmonella were of much more concern.

"I think people with deficient immune systems can be prone to infections that people with effective immune systems may not be. There's so little evidence that Mycoplasma bovis would be important as a source of human infection, particularly through the food chain.

"It's one of those examples of something that is so unlikely to happen, that I don't think there's cause for concern."