Mycoplasma bovis eradication assessed as still feasible but with major caveats

The Mycoplasma bovis Technical Advisory Group (TAG), in its latest report released today (30 October 2019), has made a judgement that eradication of the disease remains feasible. As such, the national eradication program will undoubtedly continue.

However, within its report the TAG adds major caveats as to whether or not ‘biological freedom’ from the organism will indeed be achieved. The caveats are “that the number of undetected infected herds is not large, infection has not established and spread within the non-dairy sector, and that the rate of transmission to new herds is reduced via continued shortening in the intervals from infection to application of movement controls”.

The report also acknowledges that bulk-milk testing has been finding infections outside the prior tracing network. This highlights concern that tracing networks are incomplete, and the consequent uncertainty that exists around the number of undetected infected herds.

The bare facts of the situation are that in the 27 months leading up to 25 October 2019 there have been 201 farm properties declared infected. These properties have now either had their herds slaughtered or are in the process thereof.

This number now exceeds the projected number of 192 herds needing to be slaughtered over a ten-year period, as estimated back in May 2018 when Government approved the eradication campaign.

As of 25 October 2019, there are another 297 properties under notice of direction (NOD) which prevents sale of stock except with a special permit to slaughter.

Historically, the ratio of NOD farms that are subsequently confirmed positive has been around 15 percent, with 201 so far confirmed positive and 1154 released from restrictions having been deemed to be free of the organism.

However, the criteria for NOD has changed somewhat over time so some caution is appropriate as to how many of the current NODs will be confirmed positive. MPI’s current map of NOD farms on their website says that ’70 – 80% return negative’. If this is correct, then conversely somewhere between 20% and 30% can be expected to be confirmed positive. This does seem high. It would mean 60 to 90 of these current NOD properties will go positive over coming months and require herd slaughter.

In addition, there are another 337 farms under active surveillance with blood testing. Only a small number of these are expected to be confirmed positive.

Of course, these numbers are not the end of the line. Each week there are new farms that enter the pipeline and either become surveillance farms or become NOD.

As an example, I am currently communicating with two farmers with close to 3000 dairy animals that are transitioning from NOD to confirmed positive. The source is unknown so the fan of infections from these farms and the timeframe thereof is also unknown.

The other big unknown is the extent to which it may have got into the New Zealand beef herd. We know that it has been found on more than 100 beef farms but the vast majority of these have been dairy beef.

MPI is currently taking monthly bulk milk samples from all dairy farms and testing with a bulk-milk ELISA for antibodies. This is an initial screening test which does not prove presence of the organism, but it does identify farms that then need to be blood tested.

Bulk-milk ELISA testing is a relatively new weapon in the MPI armoury that has come into play in the last 15 months.

It is the bulk-milk ELISA testing, together with early results of their latest modelling, that gives MPI some confidence that it is now catching up with the spread of the disease within the dairy herds. However, the TAG says it needs to see more evidence for this.

A key point in the TAG report is the need to get further information on beef herds. Unfortunately, the bulk milk test is no use for beef herds because there is no bulk milk to test. It is therefore crucial to any success of the program that the beef breeding herds are not currently infected.

A quick check back for the last four months suggests that there are still lots of herds going positive. There have been 25 new farms declared infected in those 17 weeks. There have been eight new infected herds in the last four weeks.

There have also been increasing levels of infection detected in the North Island, with 51 North Island farms in total having been declared infected. Northland with 19 infected farms and Waikato with 10 have become the North Island hotspots.

Despite the TAG considering that eradication remains feasible, their caveats are major. A key problem is the lack of a screening test for both beef cattle and young dairy cattle. This makes it very hard to know where to go searching for the needles in the haystack.

Perhaps the most remarkable feature of Mycoplasma bovis is the small number of farms with clinical cases. I still know of only two farms where cows have become sick, including the original identified case back in July 2017. Most of the time Mycoplasma bovis stays a silent sleeper.

Although present in all countries except Norway, I find very few overseas farmers know anything about Mycoplasms bovis. Typically, it only shows its presence when there are other stress conditions present.

Compensation is now proceeding more smoothly than previously but some people are still getting badly stuck in the system. MPI statistics include partial payments of invoices, and there are lots of farmers struggling with cash flow.

There are also lots of tragic stories out there with family breakdowns, loss of farms and worse. Most people want to keep those things private and so it stays below the public radar. Despite being away from the glare of publicity, these issues are very real and, in some cases, all-consuming for those who are affected.

The TAG remains of the view, based on genetic modelling, that the organism arrived here no earlier than December 2015. My own investigations of the transmission pathways indicate this is only possible if there were multiple strikes from a single source of semen.

This possibility is acknowledged by the TAG, that it could have arrived on three or four farms. It means that MPI’s notion of a single index farm is likely to be false.

No-one is any closer to the specifics of identifying how the disease got here.

The TAG members are largely located outside New Zealand and I am advised that this year they have communicated electronically rather than in person. This current report has been under development for more than four months.

The Government relies heavily on the TAG in relation to ongoing strategy. Given that the TAG is recommending that its next meeting should be in the second quarter of calendar 2020, then unless something fundamental changes, the program will now remain in place for at least the best part of another year.

About Keith Woodford

Keith Woodford is an independent consultant, based in New Zealand, who works internationally on agri-food systems and rural development projects. He holds honorary positions as Professor of Agri-Food Systems at Lincoln University, New Zealand, and as Senior Research Fellow at the Contemporary China Research Centre at Victoria University, Wellington.
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