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Superbug MRSA ST398 Found in British Cattle

27 December 2012

UK - The Soil Association is calling for the government to investigate British farm animals carrying MRSA (Methicillin-resistant Staphylococcus aureus) and act to stop the overuse of antibiotics in farming.

This follows new research from the University of Cambridge revealing the first cases of MRSA ST398 have been found in UK livestock.

First found in pigs in the Netherlands in 2003, MRSA ST398 has since become epidemic in European and North American pig populations and has spread to poultry and cattle.

It has not been found in British food animals before. However, very little testing has been carried out compared to other EU countries.

The superbug can cause serious and occasionally deadly infections in humans and is becoming a cause of mastitis in cows.

The high level of antibiotic resistance makes the infection difficult to treat, and the Cambridge scientists say their finding is therefore ‘of significance to both veterinary and human health’.

Scientists tested 1,500 samples of bulk milk and found seven cases of MRSA ST398 in milk from five different farms in England, Scotland and Wales.

Although there is no direct threat to human health from consuming milk, because pasteurisation will kill the bacteria, research from other countries has shown farmers, vets and abattoir workers are at increased risk.

In the Netherlands, ST398 now accounts for 39 per cent of human MRSA cases.

Although this study only tested bulk milk, it is thought likely many calves on affected farms will also carry MRSA ST398.

According to recently published Defra research, over three quarters of British dairy farms feed waste milk containing antibiotic residues to calves.

This is milk produced during the withdrawal period, after a cow has been treated with antibiotics, and is legally unfit for human consumption.

The Department of Environment, Food and Rural Affairs (Defra) showed that 21 per cent of waste milk samples contained residues of cefquinome, a modern cephalosporin.

Modern cephalosporins are the antibiotics most suspected of favouring the growth of MRSA ST398. Waste milk can also contain residues of other antibiotics associated with MRSA spread.

If calves are affected, then any meat from these animals may also be contaminated.

The emergence of MRSA ST398 in cattle could also lead to British pigs and poultry becoming affected, if this is not already the case.

Defra has refused to test British poultry becoming affected, if this is not already the case.

The Soil Association said that Defra has refused to test British poultry for MRSA, despite the Soil Association calling for such surveillance since 2007.

Richard Young, Soil Association Policy Adviser said; “This should be a wake-up call for Defra. The European Food Safety Authority recently called on all Member States to carry out regular monitoring of poultry, pigs and dairy cattle for MRSA, but unlike other countries, the UK continues to ignore this request."

"Defra must also urgently deal with the problem of waste milk containing high levels of antibiotic residues being fed to calves. There is strong evidence this has contributed to the spread of other superbugs, like ESBL E. coli, and it is also likely to make the MRSA problem on dairy farms much worse," said Mr Young.

Mr Young added that much stricter controls on modern cephalosporins is required.

These antibiotics are 'critically important' in human medicine as classified by the World Health Organisation, yet they continue to be used routinely on many cattle and pig farms.

A 400 per cent increase in the use of these antibiotics on British farms over the last decade and similar increases abroad have been linked to the growing MRSA problem in livestock.

Recent Dutch research has shown that people living in rural areas of high livestock density are also at increased risk of becoming carriers of MRSA ST398. This found that a doubling of the density of cattle increased the odds of being a carrier by over 75 per cent. Occasional hospital or nursing-home outbreaks of MRSA ST398 have also occurred in the Netherlands, showing that the bacteria can spread from person to person.

Although Cambridge scientists had previously found a different type of MRSA in British cattle, the emergence of MRSA ST398 has potential to spread far more widely in British farm animals, based on what has occurred abroad.

This is partly because the ST398 strain has the ability to acquire much higher levels of antibiotic resistance than most other MRSA strains, and the seven cases found in this study were resistant to between three and five families of antibiotics. Cases abroad have been resistant to up to 11 families of antibiotics.

A small number of cases of MRSA ST398 infections in humans in Scotland have already occurred, and earlier this year it was revealed in the minutes of a Defra meeting that human cases have also occurred in Northern England, but no details were provided.

Although MRSA ST398 can cause serious infections in humans, it is currently considered to be less virulent than ordinary hospital MRSA.

However, scientists have warned that it has a greater ability than most strains for acquiring new virulence genes, which would make it a greater threat to humans, and very recent American research has found the first-ever cases of MRSA ST398 in pigs with the highly virulent PVL (Panton-Valentine leukocidin) gene.

PVL MRSA can sometimes cause necrotising fasciitis, a flesh-eating disease, which can require infected tissue to be cut away.

TheCattleSite News Desk

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