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New mastitis threat going undiagnosed - we take a look at the symptoms and treatments

A new type of udder infection could be going widely undiagnosed on-farm and could be to blame for recurrent mastitis cases, as Aly Balsom finds out.

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New mastitis threat going undiagnosed

Hampshire vet, Dave Coombes is calling for increased vigilance and greater understanding of the signs of Mycoplasma wenyonii, which could be the underlying cause of recurrent and persistent udder changes on many UK farms.


Mr Coombes believes some farmers and vets could be misdiagnosing swollen quarters which fail to respond to treatment or reoccur as E.coli or Strep mastitis, when in fact they may be caused by wenyonii.


Up until about four years ago, there was no reliable test for wenyonii, which meant it was rarely identified. However, since the development of a PCR test, Mr Coombes of Cedar Farm Vets has seen a marked increase in incidence.


He says: “Once the test was developed, I identified wenyonii in 22 animals on eight farms within a 12-month period. That suggests it was going undiagnosed before this and I suspect that will be a situation which is mirrored nationwide. In total, the practice has seen about 40-50 confirmed cases over the last four years."

What is Mycoplasma wenyonii?

Mycoplasma wenyonii causes an infection of the lymph system in the udder and subsequently reduces milk expression. That, in turn, leads to raised somatic cell counts and clots in the milk.


It is not a mastitis pathogen itself, but it causes udder infection. That then presents with mastitis-like symptoms. Wenyonii is a different type of Mycoplasma to the more commonly recognised Mycoplasma bovis and presents differently.

How is it spread?

Wenyonii is a contagious pathogen with a vector, so the main route of spread is thought to be via needles or flies.

What are the signs of infection?

The infection usually starts with significant oedema on one quarter and can occur at any point in lactation. Occasionally more than one quarter can be involved.


The swelling is different to that caused by trauma or E.coli, as wenyonii will result in a spongy ’pitting type oedema’ around the quarter which will form a ‘pit’ or dent when pressed with a finger. This dent will then take about five-10 seconds to disappear.


Within 24-48 hours of this oedema being identified, clots will usually then appear in the milk. Early on in the infection, this milk will usually culture sterile. Later on, secondary bacterial pathogens such as Strep may be identified as a result of poor milk out due to the oedema.


When farmers treat with antibiotics and anti-inflammatories, the clots may disappear, but the problem tends to reoccur two to seven days after the treatment course has finished.

What are the treatment options?

Mr Coombes has seen the best response to treatment on his own 40-cow herd and across his client’s farms by using a combined approach of macrolide antibiotics, anti-inflammatories and oxytocin.


Often the use of oxytocin and anti-inflammatories (both non-steroidal and steroidal) have got rid of the swelling within 24 hours, but it has then reoccured. Consequently, Mr Coombes believes antibiotics are necessary. Any treatment choice should be made in discussion with the farm vet.

Are there any long-term effects?

Where inflammation of the quarter has persisted for some time, Mr Coombes has noted more swelling in the lymph nodes in the pelvis on the same side as the affected quarter.


He says: “These cows rarely get in-calf. Affected cows are found to have lymph node swelling in the pelvis, so it is possible inflammatory changes are occurring in the uterine tract, although this has not been confirmed."


This means wenyonii could be the underlying cause of culls for fertility, as well as raised somatic cell counts.


In addition, Mr Coombes has also witnessed high temperatures and respiratory disease in some cases – similar to Mycoplasma bovis – in two herds.


“I have seen cows with respiratory problems, but also very inflamed joints in all four legs. When I have aspirated the purulent joint fluid (pus) it has been found to be 100 per cent sterile. I have then identified wenyonii (from PCR blood tests),” adds Mr Coombes.

How do you prevent it?

Once wenyonii has been identified on-farm, stopping the spread is vital. Mr Coombes emphasises the importance of a ’one needle, one cow policy’.


This is particularly important if a needle has been used to deliver oxytocin to a wenyonii infected cow and is then used to aid milk let-down in a healthy, fresh calved cow as this could be a key route of infection.


Mr Coombes adds: “Really good fly control is also important. Spot on treatments are likely to be the most effective and should be used regularly through the season.”


Overall, he believes increased research into wenyonii is essential, along with greater vigilance on-farm.


“Do not assume a swollen quarter is an E.coli mastitis. Check it thoroughly and if it has got pitting oedema and no clots, it is likely to be Mycoplasma wenyonii,” he says.

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