ANALYSIS – A question mark still hangs over whether the strain of ‘super bug’ MRSA that was found recently in supermarket pork products is of UK origin or imported.
Tests conducted by the University of Cambridge identified LA-MRSA CC398 in supermarket sausages and minced pork labelled as being produced in the UK.
MRSA was first found in UK last year in a piglet. It has been shown to be “widely distributed” across the UK from isolates in pigs, horses, dairy cattle and poultry.
And while this is “emphatically not” the first signs of a public health crisis, it demonstrates how vital tackling antimicrobial resistance is on all fronts.
This is the reaction of Dr Desmond Walsh, Head of Immunity and Infections at the Medical Research Council, who wrote in an article: “It shows just how widespread antibiotic-resistant bacteria such as MRSA are, and it makes us aware of a route of transmission from farms to the wider population.
“If MRSA is infecting pigs on British farms, it could be transmitted to the wider populations via farm workers, slaughterhouses and butchers etc.”
"The public should not be overly worried by this as sensible food precautions and good hygiene should prevent its spread."
Dr Mark Holmes, University of Cambridge
Report authors from the Department of Veterinary Medicine remain tentative about whether the MRSA strain is from the UK and not imported. This is despite the food items labelled as being of UK farm origin.
The study, undertaken on behalf of the Alliance to Save Our Antibiotics, admits that cross-contamination “might have occurred” between non-UK imported meat and UK sourced product, with phylogenetic studies being required to “examine the possibility”.
Is This is a First?
LA-MRSA was first found in UK pigs in July 2014 in one piglet in Northern Ireland. In December 2014 two piglets in East Anglia were identified with LA-MRSA.
In conjunction with the British Veterinary Association, the NPA said there is no evidence that LA-MRSA on food can colonise or infect humans. Proper cooking (heating above 71 degrees celcius) and kitchen hygiene, therefore, reduces transmission risk.
What Have They Found?
MRSA is commonly associated with hospital ‘super-bug’ but Livestock Associated Methicillin-Resistant Staphylococcus Aureus CC398 (LA-MRSA: CC398) is different to the hospital strain - it has a different genotype.
The term MRSA is given to any strain of the bacteria Staphylococcus Aureus that has developed resistance to beta-lactam antibiotics.
This process does not make them more virulent but it does mean infections are harder to treat.
LA-MRSA: CC398 is a zoonosis, meaning the disease can spread between animals and humans, and is endemic in Denmark, where 29 per cent of European pig production takes place. Spain and the Netherlands also had high prevalence in the European Food Safety Authority baseline survey on MRSA in 2009.
Latest Danish Veterinary and Food Administration figures show that over 60 per cent of herds now carry the bug, which represents a meteoric rise from zero per cent in breeding stock and of 3.5 per cent in production herds since 2008.
After being the first country to recognise the problem of MRSA in 2005, the Netherlands had a prevalence of 12.8 per cent (breeding) and 17.9 per cent (production) in herds in 2009.
MRSA Prevalence in Production Units in 2008
Image courtesy of EFSA
How Can LA-MRSA Get On Food?
Various strains of MRSA have been isolated from pigs showing no signs of infection. Mucous membranes harbour the bacteria, along with skin, faeces and the rectum, as well as internal organs such as lymph nodes and lungs.
In the environment, resistant strains of Staphylococcus Aureus have been isolated from air, dust, doors and equipment.
Healthy animals and people can carry MRSA in their nostrilsand scientists have found pigs can harbour MRSA with no effect on body weight.
What Are Pork Imports Currently Like?
The UK pig industry produces around 60 per cent of the pork consumed in the UK, with 40 per cent of it being imported - 99.5 per cent of this imported product comes from the EU. Currently, this largely comes from Denmark, Germany, the Netherlands, Belgium, Poland and Ireland.
The UK's top six suppliers for all pig meat are: Denmark by quite a way, then Germany and Netherlands, with Ireland, Belgium, France and Spain providing a similar amount, according to Agriculture and Horticulture Development Board (AHDB) figures for 2014.
The AHDB published total consumption as being 25.5 per cent fresh/frozen imports, 19.1 per cent bacon imports and 15.8 per cent processed imports for last year.
Germany, Denmark and the Netherlands are all major sources of pork meat for the UK market and their herds all had higher MRSA prevalence than the EU average and the UK (14 per cent) in 2009, according to the European Food Safety Authority.
In 2009, breeding pig herd MRSA prevalence was over 40 per cent in Germany, the Netherlands and Belgium.
What Are Pig Imports Currently Like?
Live pig imports last year totalled 213,000 head in 2014. Of this, 108,000 were over 50 kilos and ready for slaughter, 105,000 were under 50 kilos and 120 were breeding animals. This is around four per cent of overall UK pig numbers, calculated at 4.8 million head in the June census.
"The Alliance to Save our Antibiotics have been warning for years that UK pig farms could develop MRSA, as they have done across Europe, and that government should be testing routinely for this."
Recently the UK has imported:
- 340,000 pigs in 2013
- 685,000 pigs in 2012
Since 2012, live pigs have been brought into the UK from Belgium, Denmark, France, Germany, the Republic of Ireland and Sweden. Outside of the EU, the UK has bought pigs from Canada and the US.
Importing pigs and pork is considered a biosecurity risk for disease in general. For this reason the National Pig Association has introduced a scheme to monitor MRSA. There are two parts to this:
- Working with pig breeding companies and the industry, the NPA has demanded “proper testing of stock before departure from the source country”. Quarantining follows of four to six weeks.
- Pig farm veterinarians send samples to the Animal Plant Health Agency for testing when pigs look unwell on farms.
These standards are voluntary because MRSA is not a notifiable disease. However, Red Tractor assurance – which covers 92 per cent of UK pork - includes the NPA import protocol and requires veterinarians to send samples into APHA.
The Soil Association has called for antibiotic usage to be minimised on farms and on the government to routinely test for MRSA.
The Guardian’s Study
An investigation by the Daily newspaper The Guardian found pork products sold in Sainsbury’s, Asda, Tesco and the Co-operative to have MRSA CC398. Nine packets – eight Danish and one Irish – were infected with CC398, of a sample of 100 packets of pork chops, bacon and gammon.
Outlining the University of Cambridge’s finding, The Guardian said: “None of the British pork tested by the Guardian was infected with CC398, but a similar study carried out by the Alliance to Save Antibiotics, a campaign group which includes the Soil Association, did identify the superbug in pork from British farms.”
The Guardian said the findings “confirm” the British pork supply chain has CC 398 from British farms.
What is the Risk Onfarm?
Most cases of MRSA are associated with farmers and stockmen. How the patient reacts varies from cases to cases, although generally, the reaction is a skin infection manifesting itself in a rash.
The bugs are very good at living up the noses of pigs but not so well adapted to man. Down the food supply chain, abattoir workers and people in food processing are also at risk, meaning precautions like covering cuts and regular hand-washing are advised.
Some people have developed blood poisoning and it has affected babies through umbilical cord infections.
As for the antibiotics themselves, obligatory withdrawal periods, often of 28 days, are placed on antimicrobial products for food animals.
This means an animal does not receive antibiotics for a predetermined time before the date of slaughter. For this reason meat and milk should not contain antibiotic traces.
An Antibiotic Free Label for Meat
With consumers aware of the dangers of antibiotic resistant bacteria, a label denoting meat produced in systems free from antibiotics could demand a premium price.
This could also follow a tightening of legislation around the use of antimicrobial drugs, spearheaded by the World Health Organisation.
An article in The Guardian said: “What health campaigners want is for retailers and suppliers to demonstrate plans to phase out routine prophylactic use of antibiotics, including a ban on the mass use of medication in feed.
“However, they pointedly criticise the recent attention given to antibiotic-free labels on food.”
A blanket approach to banning antimicrobials in a livestock production system could compromise animal welfare, as well as splitting meat products into a two-tier market – those with antibiotics, and those without.
Sick animals may go untreated because of a reluctance to lose the label. There is also the possible issue of heightened biosecurity measures restricting barn enrichment.
EU law states pigs must be able to access manipulable items to work the snout in foraging activities, which, in a high biosecurity system, poses a disease threat, along with anything else coming in from the outside.
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Top image via Shutterstock