On July 22, 2017, New Zealand’s Ministry of Primary Industries (MPI) confirmed the first detection of Mycoplasma bovis (M. bovis) in New Zealand in a dairy herd in South Canterbury, a region on New Zealand’s South Island.
Routine surveillance helped identify the first positive M. bovis case, which raised significant concern. However, when the fourth farm – which was unrelated to the first three cases from associated farms – tested positive, it was clear the incident was not a random or contained disease.
It was bigger, with the potential to get significantly larger if it couldn’t be brought under control quickly. The New Zealand government chose to set up a national M. bovis surveillance program to determine the risk to their dairy industry.
New Zealand dairy farmers wanted eradication
“Pressure came from dairy farmers because they didn’t want to lose the premium value of their primary industry,” says Alison Digney, product manager with Thermo Fisher Scientific, based in Australia. “Dairy is a key industry in New Zealand, and its global image is contingent on its reputation as the cleanest producer in the world.”
Currently, the New Zealand government is in the process of assessing the extent of disease spread using bulk milk testing and animal traceability. Since then, an additional 24 properties have been identified with M. bovis-infected cows, with the majority located on South Island. All 28 infected properties will be depopulated, and surveillance will continue until all new lactating cows have been screened.
From the start of the program through April 2018, MPI estimates the operational costs of the program at $25.6 million (NZ$35 million) and compensation liabilities at $44 million (NZ$60 million). The New Zealand government has approved $62 million (NZ$85 million), and industry associations have committed $8.2 million (NZ$11.2 million) in response funding.
“The decision taken to depopulate infected farms will reduce disease pressure and put us in the best position to move to long-term management,” Digney says. “New Zealand wants to maintain its image as a global leader in the dairy industry.”
New Zealand M. bovis surveillance strategy
New Zealand’s MPI launched a very progressive surveillance and testing approach to try to map where M. bovis is located in an effort to determine how to manage it while also looking for clues about how it arrived in New Zealand herds.
Real-time polymerase chain reaction (PCR) diagnostic tests are being used to screen bulk milk from every dairy herd in New Zealand, which means every lactating cow is being screened within 10 days. If a positive bulk milk sample is identified, the individual cows in that herd are tested. Then the entire process will be repeated in six months for a dairy’s new lactating animals.
PCR testing was chosen because it allows bulk milk testing with lab results available very quickly. The ability to test pooled samples from different animals with PCR becomes a great value when testing a large number of samples. By detecting the bacterial DNA in the sample, PCR gives information about currently infected animals.
Beyond testing, biosecurity measures restricting the movement of goods and animals have been placed not only on infected farms but farms that are high-risk as well. MPI continues to hold public and farmer meetings to keep people informed about the situation and how to protect their farms. In addition, culling cows that have tested positive has started.
Why take mycoplasma infections so seriously?
There is no treatment available when mycoplasma mastitis hits a herd, so if early diagnosis of an outbreak is possible, immediate separation of clinical cases into hospital pens is recommended to see if animals improve. However, there is a lack of strong scientific evidence demonstrating mycoplasma clears completely from the animal’s system.
Regardless of the country where outbreaks occur, lack of M. bovis detection is part of the problem.
“Despite what we have seen in the diagnostic lab over the years, I don’t believe mycoplasma has been consistently reported, mainly because of the difficulties in diagnosis,” says Dr. Robin Nicholas, a mycoplasma consultant. “It’s not been an easy pathogen to culture.
Unfortunately, in diagnostic labs around the world, there haven’t been many people involved in the diagnosis and search for mycoplasma who have understood how to handle and culture it. Now there are new tools that make it easier to test, and we have increased the awareness of mycoplasma.”
Mycoplasmas differ from other mastitis pathogens because they lack a cell wall. Without a target, like a cell wall, some antibiotics are ineffective against mycoplasmas.
“In the research I’ve been part of, we’re actually seeing resistance to most of the antibiotics which are commonly used in the field for bacterial diseases,” Nicholas says. “Mycoplasmas have high mutation rates and, despite their small size, they contain sophisticated mechanisms which are able to combat the immune system and even antibiotics.
A few years ago, we also discovered mycoplasmas can grow in a biofilm, which are adherent cells covered in a carbohydrate matrix. In this form, they are more resistant to both antibiotics and the host immune system – and even things like heat, biocides and desiccation.”
“We believe the biofilm is the natural state of mycoplasmas in the host where they may be more virulent, and this makes them extremely difficult to treat, let alone destroy,” Nicholas says.
New research is now underway to better understand the role biofilm plays in mycoplasma mastitis, where it may block ducts in the udder.
Mycoplasma is also different in how it can attack the animal’s body. There are typically two scenarios – one for cows and one for young calves.
“In cows, the mycoplasma is introduced into the udder, causing mastitis, and then it moves into the bloodstream and may shift to the joints, where it can cause significant damage and pain,” he says. “The disease enters the calf’s lungs, causing pneumonia, and can end up causing swollen joints because the mycoplasma is transmitted through the bloodstream.”
Mycoplasma infections are typically triggered by stress factors, like calving, transport or even weather changes and, once initiated, this enables the spread to other animals in the herd.
“What we’ve seen with mycoplasmas around the world is: When mycoplasma is introduced to a naïve herd, this can initiate an explosive outbreak in the herd,” he says. “Naïve animals will go down very, very quickly, while carriers only show mild clinical signs.”
How did M. bovis arrive in New Zealand?
The manner in which M. bovis entered New Zealand’s dairy herd is still under investigation. No animals have been imported for at least three years, according to news articles based on MPI comments.
For New Zealand, the original source of the initial infection is still unknown; however, investigations point to illegally imported treatment materials that were administered to dairy cattle, according to news reports. 
PHOTO: No treatment is available when mycoplasma mastitis hits a herd, so if early diagnosis is possible, immediate separation of clinical cases is recommended to see if animals improve. Photo provided by Sarah Mikesell.
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Ivan Leyva-Baca
- Product Application Specialist
- Thermo Fisher Scientific
