Keith Woodford shows that the more you know about the Mycoplasma species, the more complex the management issues become for eradicating Mycoplasma bovis

By Keith Woodford*

Currently, there is a fervent ‘behind-the-scenes‘ debate as to whether eradication of Mycoplasma bovis from New Zealand is feasible.

It is well over a month, possibly close to two months, since the international Technical Advisory Group (TAG) voted six to four in favour of eradication being feasible. This would have been based on information supplied to them by MPI and assessed over a telephone hook-up. New evidence since then provides further complexity and concerns.

First, there is extensive evidence from overseas that Mycoplasma bovis can transfer between species and that it can infect sheep, goats, pigs, deer and even poultry. Strictly speaking, this is not new evidence as it was sitting there all along in the scientific literature and easily found. However, the implications of this within the New Zealand environment have not been considered to date.

Second, there is a new line of evidence (not yet published) of a likely outbreak of Mycoplasma bovis in the South Island back in 2014. Both of these issues have potential to complicate the eradication campaign.

In this article, my focus is on the potential for cross-species infection. I will be writing about the new evidence for earlier arrival in a follow-up article.

I was recently alerted to the importance of the cross-species issue by a briefing paper undertaken by retired Wanaka vet Gilbert van Reenen. This paper was commissioned by a concerned third party for presentation to the Minister of Agriculture. 

To quote van Reenen’s words: “there is now abundant reliable, scientific evidence that M. bovis has crossed the host species barrier from cattle to deer, bison, buffalo, goats, sheep, pigs and poultry in a range of [overseas] environments”.

I have gone back and checked the scientific references that van Reenen has used. The evidence does stack up. The only room for debate is the risk of this occurring in the New Zealand environment.

One paper describes how wild pigs were the transmission source in alpine Austria. This paper is particularly chilling in the New Zealand context, given the ubiquitous presence of pigs in our New Zealand back country. Evidence it can also occur in poultry further illustrates the robustness of this bacteria to survive and thrive under specific conditions in very different animal species.

Wild pigs are unlikely to be found on most dairy farms, but that cannot be said for many of the beef farms that grow out the bull and steer calves from dairy farms. An increasing number of New Zealand’s infected farms are beef farms.  Wild pigs love dead carcasses and so anything that dies from Mycoplasma bovis will have been scoffed up by any resident pigs.

The evidence for deer relates mainly to whitetail deer, but there is also evidence for what we call Canadian elk which is a subspecies of Cervus elaphus, which we know as ‘red deer’. Indeed, many of our farmed red deer are actually crosses between European red deer and Canadian elk.

There is also evidence that the bacteria can survive for up to eight months in calf-shed bedding. Until now, MPI has worked on the basis of disinfection plus two months maximum life will see the bacteria destroyed. The good news is that Mycoplasma bovis hates disinfectants.

Before going into panic mode, it is worth reminding ourselves that Mycoplasma bovis has been around for many thousands of years – it did not suddenly arrive from outer space. It is generally regarded internationally as a relatively minor disease that can be managed but not eradicated.

 The evidence that Mycoplasma bovis crosses the species barriers has been known by some of the MPI scientists for many months. For example, the MPI Pathways Report prepared in November 2017, but not released publicly until March 2018, gives consideration to species other than cattle being the way the disease came into New Zealand.

MPI’s judgement, which in this case seems very reasonable, is that it is unlikely for Mycoplasma bovis to have come into New Zealand via these other species, but they cannot be totally discounted as the source. More importantly, now that the disease is in New Zealand, these other species have potential to provide a disease reservoir. This is something that MPI has not publicly discussed.

The situation with sheep is more complex than some other species, with sheep being particularly susceptible to the very closely related Mycoplasma agalactiae. Until the mid 1970s, Mycoplasma bovis and agalactiae were considered the same species.

It is evident that Mycoplasma bovis and agalactiae have the same common ancestor, but each has evolved to now have a favoured host. However, Mycoplasma bovis can definitely survive in sheep and goats and thereby provides a viable disease reservoir. When Mycoplasma bovis infects sheep, it may or may not show symptoms, just as occurs in cattle.

It also needs to be understood that there are many Mycoplasma species other than Mycoplasma bovis, including some others that are found in cattle here in New Zealand, and many that are also found in humans.

Have we actually done the right thing in placing Mycoplasma bovis on a pinnacle of ‘Dreaded Disease Number 2’ (after foot and mouth)? There is no easy answer to that one.

Let’s remind ourselves that Mycoplasma bovis is typically a secondary disease that shows up when stress is present. The New Zealand practice of feeding calves with non-pasteurised ‘hospital cow milk’, and perhaps some other veterinary practices, may well have greatly facilitated its spread.

Let’s also be grateful that we don’t cull humans when they too go Mycoplasma positive. Some of the readers of this article will themselves in all likelihood be Mycoplasma positive, although highly unlikely to be the bovis species of Mycoplasma.

There are at least 125 Mycoplasma species and at least 15 of these have humans as the primary host. They cause a range of human diseases and pass directly between humans without need for other animals as intermediary hosts.

If this all sounds real scary, then just remember that humans, cattle and Mycoplasmas have all been in this world for a long time. Mycoplasmas do cause health problems but most of the time they stay below the radar and we all get along just fine.

As for the specifics of Mycoplasma bovis transferring to humans, that is highly unlikely. It does not particularly like humans, and in any case it is totally destroyed by milk pasteurisation and cooking of meat. There are hundreds of other diseases that are a great deal more important for humans.


*Keith Woodford was Professor of Farm Management and Agribusiness at Lincoln University for 15 years through to 2015. He is now Principal Consultant at AgriFood Systems Ltd.   His articles are archived at http://keithwoodford.wordpress.com. You can contact him directly here.

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21 Comments

Fascinating series of articles Keith. 'Unlikely' seems to pop up quite a lot. Are MPI giving any calculations or do they just make a judgement call based on what evidence they have gathered to date?

Hamish,
One of the problems with MPI is that PR massagers have huge difficulty in dealing with uncertainties. Bureaucrats and leaders in general believe they look weak if they talk in any terms other than certainty. In that regard I give the Minister credit for being upfront in saying that eradication may or may not work. In that context, it is important that admitting defeat is a politically acceptable outcome, because that may well be necessary. We need to make sure that eradication off-ramps remain firmly in place.
One of the issues with Mycoplasma,bovis is that all of the ways that it got here are supposed to be essentially low probability, yet one of them happened. One of the key assumptions of MPI currently is that the disease only got here just over two years ago. They have been unwilling to countenance that it might have been here a lot longer, despite mounting evidence for that. Telling more of that story, including the new emerging evidence, will be my next post on Mycoplasma. And the longer it has been here, the more difficult it will be to eradicate.
Keith W

I have been finding these articles quite interesting.

It is clear M-Bovis is here to stay, so anything we do for eradication seems to now be money down the drain.

Best to spend the money on adequate management going forwards. Rather than in 10 years when the eradication has failed.

Good article, Keith. It's clear that we have ourselves an adaptable little organism here: able to transmogrify according to its environment yet not a host-killer. Your comment upthread is spot-on: large organisations and especially their PR arms are congenitally unable to handle uncertainty, error bars, or the usual caveats that real science always places around its results.

The way forward is to allow a political soft landing for the notion that containment/eradication is futile, and maintenance/management at a safe level is all we have. With every other dairy country except Norway dealing with exactly the same issue, at least there is good experience to draw on.

But the absolutist 'Ex-Ter-Min-Ate' chant issuing from the MPI-leks has to be scuttled first.

Waymad,
I agree that we do have to engineer a political soft landing. That is real challenging given that we tried to fly the plane while it was still in the early stages of construction. The Government is now searching for the parachutes.But from a political perspective, they don't want to call 'jump' without a consensus. They need to be able to say that we did our best given the cards we were dealt. The industry and political focus now is on the ACE. (The C and the E are for 'covering event'. You can work out what the A stands for.)
KeithW

I heard something about this from a Fonterra employee with a lifestyle block down the line. I'd just done a drive the weekend before through the backblocks from Port Waikato to Huntly, and the number of wild goats at the roadside beside dairy herds.. well, if MPB can be transmitted from goats to cows and vice versa, there is no chance of containing it.

Oddly enough, biodiversity is less of a problem than monoculture-to-the-horizon, when transmission is the problem :)

At least it will be over quickly and comprehensively

"...it is totally destroyed by cooking."

Should precautions be highlighted then in the precooking preparation of the meal if MPB meat is entering the food chain? Hands, dog food scraps, meatboards, benches etc otherwise by the sound of it uncooked meat can just be another source of re-infection.

Mmmm, well done rib eye steak.

Smalltown,
The risks are trivial compared to other zoonoses (pronounced' zoo-no-sees') which are diseases that pass from animals to humans. There are many hundreds of these diseases. Accordingly, anyone who drinks raw milk or uncooked milk is a big risk taker. Even owning a pet such as a cat involves risk of disease transfer. But most would say it is best not to get too paranoid about these things - we would all go crazy if we did. Risk assessment is always tricky and it is challenging to keep the risk relativities in perspective. Mycoplasma bovis is way down the list.
KeithW

The dairy industry bought into the forestry industry here in the south waikato, central plateau region. Trees were cut down and cowsheds built. There are pigs aplenty. What was once the backblocks is now highly industrialised dairy farming. But the wild pigs still have lots of gullys and bush reservoirs to hide.
This is now a Beef farming problem. The dairy beef industry is huge in New Zealand. Dairy cross hereford and angus calves are a mainstay of the beef industry.
The feral goats pigs and deer are everywhere. Dairy beef calves have been moved everywhere. Eradication of a tiny bacteria that can infect all and sundry is a silly dream.

Are you up worrying at 4.00 am or just starting work?
Bull beef finishers are worried round here, could be the end of an industry that started in the late 60's and really got going in the 90's. Supplying low fat bull beef because we had a quota into the USA and they had surplus fat.
Now the USA doesn't really need us, who wants to eat a 2 year old bull? Either way it's the main stay of a lot of farmers and this could radically change the industry.

Worry Aj, who me? Sleep can be a bit elusive as you get long in the tooth. I do have concerns for bull beef. There does seem to be less requirement from the US, yet all of a sudden we are producing more. I am actually feeling a little over the whole farming thing. Kates comment below is on the button.

To pretend there is no difference between a corporate type farm and an intergenerational family farm, bugs me.

Yeah perhaps I was being a bit blasé about the whole thing. Kate certainly has a point. And so does Casual Observer. From my perspective most weeks I am sending stock off to their deaths. They are young of course. Noone wants an mutton chop any more. So a cull wouldnt exactly be just another day...but not far off. But in saying that, I dont look at their faces anymore when they are heading for the truck. It makes me feel like shit. Thats why I agreed with Kate, on certain days you have to turn your brain and emotion off.

Belle, it was always a problem with me, every thing I farmed died, I hated shipping off lambs, 2yr bulls not so bad, ewes and cows very hard. It's what makes you a great farmer.

Let’s also be grateful that we don’t cull humans when they too go Mycoplasma positive.

A deliberately emotive comment. And there are a lot of these going around.

There was something on the news last night about how difficult culling is because farmers love their animals .

Our language around this is as if these cows are pets, owned for companionship and that if the infected animals were not culled, then they would live out their lives grazing happily in the sun until old age got them.

And when their time was up, we'd 'put them to sleep', have them cremated, and bury them in the back paddock with a headstone reminding us of their lifelong devotion and companionship.

I think we have to keep reminding ourselves that these animals are economic units which will be culled as soon as they cease to be economic. And when they do fail to produce, they get loaded on a truck and sent to the works.

So if I take this example and turn it into an analogy with humans, I would write:

Let’s also be grateful that we don’t cull humans when they too become economically unproductive..

My point being, drawing this type of analogy is just plain silly. There is nothing inhumane, or morally wrong about the initiative to attempt to eradicate the disease as is implied by these human analogy type of comment.

It all comes down to perceptions Kate. What you see as an emotive comment, I see as black humour. For some farming families their cows or some of them, are the equivalent of pets. Calves that are reared for Pet Day at primary school, or just cows like our 'No 75' who was around when our kids were young - she was always at the back when going to and from the shed, was very quiet, loved you to stroke her face and our kids, as toddlers, would love to ride on her back. To the kids she was 'special'. When she was no longer productive she got to live out her life until she had to be put down. They were as upset that she had died as they were when the dog died. You haven't walked in m bovis affected farmers shoes, Kate, so don't judge them. Yes there are farms where cows are simply a unit of production - but for many owner operators/smaller farmers and their families to have to destroy a perfectly healthy cow that they have come to love like a pet, can be an emotional journey.

I'm guessing that your uneconomic 'No 75', who was literally put to pasture to live out to a natural age-related death, was the exception in your herd/operation however.

She became a pet, but not all your animals became pets, did they?

Sure, you got to know each animal by their odd looks/quirks/habits and behaviours - and yeah, you liked the company of these animals, but can you say you loved them?

I'm not judging m bovis affected farmers at all. All I'm saying is that we are using the word "love" in a very odd, and disingenuous way. When every one of my pet dogs have died, I cried and I hurt that they were gone, but I always went out and got another pet dog - a replacement.

When people we love die, they are generally never replaced in our minds or our hearts.

What I'm saying is farmers don't love their production units, anymore than I loved my dogs - both are replaceable. Sure, there is distraught - big distraught - and massive work to be done to get back up the genetics/temperament that you might have bred over the years, I really, really get that.

But it isn't like losing a loved one. That's all I'm saying.

I'd liken losing your herd to being made redundant from a job. Or losing an entire crop of produce. You pick yourself up and start again, or you go in another direction in life. This type of thing happens to people in society both on and off the farm.

Agree to disagree on this one Kate. Oxford definition of 'love' is An intense feeling of deep affection. https://en.oxforddictionaries.com/definition/love
As to No75 being replaceable - no she wasn't - not in the hearts of the kids. Different people have different capabilities for love. Love is a feeling and as such is an emotion. Emotions are not always rational in the eyes of others, but that doesn't mean they aren't real to the person feeling the emotion. As also a crop grower, I would have nothing like the feeling of loss of a herd of cows I had spent decades building genetically, if I lost a years production of our cherries - or even the trees themselves. However there may be other orchardists/growers who would disagree with that - I respect that their feelings may be different to mine. I will not judge them on it.