Superbug MRSA ST398 found in British cattle

21 December 2012

The Soil Association is calling for the government to investigate British farm animals carrying MRSA and act to stop the overuse of antibiotics in farming. 

This follows new research from the University of Cambridge [1] 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 [2] 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 [3].

The superbug can cause serious and occasionally deadly infections in humans and is becoming a cause of mastitis in cows [4][5]. The high level of antibiotic resistance makes this 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% of human MRSA cases. [6]

Although this study only tested bulk milk, it is 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 [7]. This is milk produced during the withdrawal period, after a cow has been treated with antibiotics, and is legally unfit for human consumption. Defra showed that 21% of waste milk samples contained residues of cefquinome, a modern cephalosporin [8]. 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 for MRSA, despite the Soil Association calling for such surveillance since 2007 [9].

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. We are lucky independent researchers identified this problem at an early stage. We are calling for comprehensive surveillance to be established before it gets out of hand.

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. We are keen to work with the industry to address this challenge and call for a ban on feeding calves waste milk from cows that have recently received antibiotics, unless the milk can be treated to destroy antibiotic residues and kill resistant bacteria while ensuring the resulting milk is still sufficiently wholesome to be fed to calves.

We also need much stricter controls on the use of the modern cephalosporins. These antibiotics are classified by the World Health Organisation as critically important in human medicine, yet they continue to be used routinely on many cattle and pig farms. There has been a 400% increase in the use of these antibiotics on British farms over the last decade and similar increases have occurred abroad. Many scientists believe this to be the main reason for 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% [10]. 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 [11], 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 [12].

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 [13].

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 [14], 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 [15]. PVL MRSA can sometimes cause necrotising fasciitis, a flesh-eating disease which can require infected tissue to be cut away.

ENDS

For press enquiries contact the Soil Association press office:
Natasha Collins-Daniel, Press Office Manager – 0117 914 2448 / 07827 925380
Ncollins-daniel@soilassociation.org

Notes to editors
[1] Paterson et al., 2012. First detection of livestock-associated meticillin-resistant Staphylococcus aureus CC398 in bulk tank milk in the United Kingdom, January to July 2012, Eurosurveillance,17, http://eurosurveillance.org/ViewArticle.aspx?ArticleId=20337
[2] MRSA ST398 has been found at the abattoir in 61% of Spanish pigs, in 60% of Germany pigs and 39% of Dutch pigs. See:
http://www.ncbi.nlm.nih.gov/pubmed/22251394
http://www.ncbi.nlm.nih.gov/pubmed?term=st398%20germany%20abattoir
http://www.ncbi.nlm.nih.gov/pubmed/17367960
[3] In 2009, Defra carried out an MRSA survey of pig farms as part of mandatory EU surveillance. No MRSA was found, however the method used involved testing dust samples rather than samples taken directly from the pigs, which would have provided more sensitive testing. In 2008, Defra scientists carried out an MRSA survey of 940 milk samples from cows with mastitis which initially did not find any positive cases. However, when new tests were developed it was subsequently shown that a dozen cases were a new type of MRSA (not ST398). Defra has never carried out any MRSA survey of poultry, despite knowing that live poultry are imported from European countries like Belgium and the Netherlands which have MRSA ST398 in their poultry flocks.
[4] Lozano et al., 2011. Empyema caused by MRSA ST398 with Atypical Resistance Profile, Spain, Emerging Infectious Diseases, 17: 138-40, http://wwwnc.cdc.gov/eid/article/17/1/pdfs/10-0307.pdf
[5] Tavakol et al., 2012. Bovine-associated MRSA ST398 in the Netherlands, ActaVeterinaria Scandinavia, 54: 28, http://www.actavetscand.com/content/pdf/1751-0147-54-28.pdf
[6] Nethmap Maran, 2012. http://www.uu.nl/SiteCollectionImages/Fac_DGK/Nieuwsplaatjes/Nieuws/2012/NethmapMaran_Web.pdf
[7] Brunton et al., 2012. A survey of antimicrobial usage on dairy farms and waste milk feeding practices in England and Wales, Veterinary Record, 171: 296, http://www.ncbi.nlm.nih.gov/pubmed/22903925
[8] Horton et al., 2012. Concentrations and remediation of cephalosporin residues in waste milk from dairy farms in England and Wales, http://registration.akm.ch/einsicht.php?XNABSTRACT_ID=142425&XNSPR%20ACHE_ID=2&XNKONGRESS_ID=161&XNMASKEN_ID=900
[9] Nunan and Young, 2007. MRSA in farm animals and meat, http://www.soilassociation.org/LinkClick.aspx?fileticket=%2BmWBoFr348s%3D&tabid=385
[10] Feingold et al., 2012. Livestock Density as Risk Factor for Livestock-associated Methicillin-Resistant Staphylococcus aureus, the Netherlands, Emerging Infectious Diseases, 18: 1841-9, http://wwwnc.cdc.gov/eid/article/18/11/pdfs/11-1850.pdf
[11] Garcia-Alvarez et al., 2011. Meticillin-resistant Staphylococcus aureus with a novel mecA homologue emerging in human and bovine populations in the UK and Denmark: a descriptive study, Lancet Infectious Diseases, 11: 595-603, www.thelancet.com/journals/laninf/article/PIIS1473-3099(11)70126-8/abstract
[12] Jamrozy et al., 2012. Comparative Genotypic and Phenotypic Characterisation of Methicillin-Resistant Staphylococcus aureus ST398 Isolated from Animals and Humans, PloS One, 7, http://www.plosone.org/article/fetchObjectAttachment.action?uri=info%3Adoi%2F10.1371%2Fjournal.pone.0040458&representation=PDF
[13] Defra Antimicrobial Resistance Coordination Group (DARC), 2012. Report of meeting held on 1 February 2012, http://www.vmd.defra.gov.uk/pdf/darc_mrsa_MinsFeb12.pdf
[14] Schijffelen et al., 2010. Whole genome analysis of a livestock-associated methicillin-resistant Staphylococcus aureus ST398 isolate from a case of human endocarditis, BMC Genomics, 11: 376-85, http://www.biomedcentral.com/content/pdf/1471-2164-11-376.pdf
[15] Osadebe et al., 2012. Prevalence and Characteristics of Staphylococcus aureus in Connecticut Swine and Swine Farmers, Zoonoses and Public Health, http://www.ncbi.nlm.nih.gov/pubmed/22883566