3 June 2011

A new strain of the superbug MRSA has been found in British cows. While the superbug is believed to currently affect humans at a low rate, the researchers behind the discovery have said “it does appear that the numbers are rising.” They say their discovery is “potentially of public health importance.”

Methicillin-resistant Staphylococcus aureus (MRSA) is a drug-resistant form of bacteria which can be deadly when it infects wounds. Some have speculated that an overuse of antibiotics could be to blame for creating the resistant bug. Dr Mark Holmes, Senior Lecturer in Preventive Vet Medicine at Cambridge University, who made the discovery, confirmed this as a "credible hypothesis."image expired

Dr Holmes and Dr Laura Garcia-Alvarez discovered the new strain while studying a bacterium known to cause mastitis in cows. Writing in Medical journal The Lancet, the researchers said there is no evidence of a health risk from consuming milk and dairy products as pasteurisation kills all MRSA bacteria. However, Dr Garcia-Alvarez commented that finding the new strain in both in humans and cows was "very worrying".

The Cambridge team stumbled upon the new strain while testing milk from a farm in southwest England in 2007. Further investigation established that it also existed at other dairy farms across the UK. The new strain has also been found in samples of Staphylococcus aureus taken from people in Scotland, England, Ireland, Denmark and Germany; the oldest of these came from a Danish patient in 1975, implying the strain has existed for 35 years.

This is the first time MRSA has been found in livestock in the UK. The scientists who discovered the strain found the MRSA bacteria in 13 of 940 samples taken from 450 dairy herds in England.  Samples taken from screening tests and people treated for MRSA led researchers to estimate levels of infection to be “in the range of one in 100 to one in 500 of total MRSA in the UK and Denmark.”

Farming groups react to study

In light of Alvarez and Holmes’ research, published today in The Lancet, The Soil Association has called for a complete ban on the routine use of antibiotics, which it believes promotes the development of drug-resistant bacteria. It also called for an end to the economic pressure put upon farmers to cut costs in order to maintain low prices; these sentiments echo comments made by the Cambridge team, who spoke of the “tremendous financial pressure” put on farmers by supermarkets.

Helen Browning, Director of the Soil Association, lambasted the system which she claims is jeopardising human health for the sake of profit. Browning said, “In the relentless drive for increased per animal productivity, and under acute price pressure, dairy systems are becoming ever more anti- biotic dependent. We need to get farmers off this treadmill, even if that means milk has to cost a few pennies more. That would be a very small price to pay for maintaining the efficacy of these life-saving drugs.”

The National Farmers' Union has responded to the news by reiterating its adage that veterinary medicines should be used ‘as little as possible, but as much as necessary.’ NFU chief dairy adviser Rob Newberry maintained that the welfare of cows was of "paramount importance" to British dairy farmers.image expired

Newberry told the BBC, "In the interests of human and animal health, and animal welfare, it is important that veterinary medicines are administered as little as possible but as much as necessary. Any antibiotic or veterinary medicine being administered to a food producing animal has strict conditions of use, including milk and meat withdrawal times, and in general, under European law, would only be available under prescription."

However, A Freedom of Information request submitted by the Soil Association to the Veterinary Medicines Directorate (VMD) revealed that the veterinary use of modern cephalosporin anti-biotics has more than quadrupled over the past decade, in spite of pressure from the World Health Organisation (WHO), the European Medicines Agency and the former Chief Medical Officer, Sir Liam Donaldson, to curb their use on farms. Industry pressure successfully saw attempts to ban the direct marketing of veterinary medicines to farmers rejected in January this year.

Government reaction, Cambridge group to conduct further research

Commenting on the Cambridge researchers’ discovery, a spokesperson for the Department of Health said, "From the available evidence, we understand this new form of MRSA is rare in the UK and is not causing infections in humans. However, our expert committee, ARHAI, will be reviewing this issue at their next meeting and will consider potential medical, veterinary and food safety issues."

A Food Standards Agency spokesperson agreed that the study did not provide any direct evidence that humans are currently being infected the new MRSA. He wished to assure consumers that, "The risk of contracting this new strain of MRSA through drinking milk is extremely low because the vast majority of cows' milk is pasteurised and the pasteurisation process destroys all types of MRSA."

With funding from the Medical Research Council, the researchers will undertake prevalence surveys in people and in dairy cattle in the UK, with the aim of determining levels of the new MRSA present in these populations. They will also perform an epidemiological study on farms to identify any factors that may be associated with infection by the new MRSA, to look for further new MRSA strains, and to explore the potential risks of the new strain to farm workers.

In several other European countries, new strains of MRSA have been found in pigs and poultry as well as cattle and have, in the past, infected humans. British pigs appear so far to be free of MRSA, but no testing has been carried out on poultry despite the fact that the UK imports live poultry from countries known to have MRSA in their flocks. The Soil Association has called for the urgent introduction of a comprehensive programme to test farm animals, farm workers, veterinary surgeons, milk, meat and farm waste for MRSA, which it says would bring the UK into line with several of our EU partners.

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