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Study of Salmonella, Toxoplasma, Hepatitis E Virus, Yersinia, Porcine Reproductive and Respiratory Syndrome Virus, Antimicrobial resistance in Campylobacter coli and Extended Spectrum Beta Lactamase E. coli in UK Pigs at Slaughter

13 March 2014

There was a consistently lower prevalence of bacteria (Salmonella and Yersinia) found on the pig carcass than carriage of the same microorganisms in the animal. This shows the effectiveness of the dressing procedures in the abattoir to limit the contamination of pig carcasses and thereby control the risk of exposure of consumers to potentially harmful microorganisms.

Salmonella

Salmonella is the second most commonly reported cause of food poisoning, behind Campylobacter, in the UK. In 2009, 108,614 human cases of salmonellosis were reported in the EU. Under-ascertainment of infectious intestinal disease is well recognised, hence the true population burden of infections is likely to be far greater.

There has been a reduction in the number of reported human cases of Salmonella over the past five years, which is in part due to the successful implementation of Salmonella national control plans in the poultry sector. However, given the reduction in risk from poultry meat and eggs, the role of pork and pork products and the relative number of human cases of salmonellosis attributed to such products may rise, even though the actual numbers may change little.

  • A total of 619 caeca, 624 carcass swabs and 625 rectal swabs, from 626 pigs, were tested for Salmonella.
  • After accounting for clustering of pigs within farms, the prevalence of Salmonella in the caecal samples was 30.5 per cent (95% CI 26.5-34.6) and the prevalence in the carcass swab samples was 9.6 per cent (95% CI 7.3-11.9).

Toxoplasma

The intra-cellular protozoan, Toxoplasma gondii, is widely prevalent in humans, warm-blooded animals and birds throughout the world. An estimated 350,000 people become infected with Toxoplasma each year in the UK, of which 10 to 20 per cent are symptomatic. Although the clinical signs are usually mild, infection can be associated with serious sequelae including eye disease and disability. People who are immunocompromised and pregnant women newly infected with Toxoplasma are particularly vulnerable; in the latter, miscarriage, stillbirth and deformities of the child can occur.

Tissue cysts are highly infectious for humans and other animals and, in addition to direct transmission from cat faeces or material from aborting sheep, undercooked meat has been identified as an important source of human infection.

  • A total of 620 plasma samples, from 620 pigs, were tested for Toxoplasma.
  • After accounting for clustering of pigs within farms, the seroprevalence of Toxoplasma was 7.4 per cent (95% CI 5.3-9.5)

Hepatitis E Virus

The hepatitis E virus (HEV) is one of the five viruses in humans which principally cause hepatitis (an inflammation of the liver). The clinical illness in humans is called hepatitis E.

Until recently, hepatitis E has been considered in the UK as an exotic infection only acquired by travel to those areas of the world where HEV is endemic. It is now recognised that the majority of cases of hepatitis E occur in people who have not travelled outside the UK, these are by definition indigenous to the UK. In developed countries, including the UK, it is now widely accepted that the virus in humans represents a zoonosis acquired through the consumption of undercooked or raw meat and also perhaps consumption of shellfish.

A total of 640 plasma samples, from 640 pigs, were tested for Hepatitis E virus.

  • After accounting for clustering of pigs within farms, the seroprevalence of Hepatitis E virus was 92.8 per cent (95% CI 90.7-95.0).
  • The prevalence of current infection, defined by the presence of detectable plasma HEV RNA, adjusting for clustering of pigs within farms, was 5.8 per cent (95% CI 3.9-7.6).

Yersinia spp.

Yersiniosis caused by the bacterium Yersinia enterocolitica is a zoonotic gastrointestinal disease. Infection with Y. enterocolitica can cause fever, abdominal pain and diarrhoea. Chronic illness and reactive arthritis have also been reported as sequelae of Y. enterocolitica infection.

The number of confirmed human cases of Y. enterocolitica and other Yersinia spp. in the UK has declined in recent years with 55 confirmed cases in 2012. The number of cases in the UK are low compared to other European countries due to the low consumption of raw pork in the UK. Pigs are considered to be the primary reservoir of human pathogenic Y. enterocolitica strains, mainly because of the high prevalence of such strains in pigs and the high genetic similarity between human and porcine isolates.

  • A total of 624 carcass swabs and 620 tonsil samples, from 624 pigs, were tested for the presence of Yersinia.
  • After accounting for clustering of pigs within farms, the prevalence of Yersinia was 32.9 per cent (95% CI 28.8-37.0) for tonsil samples, and the prevalence in the carcass swab samples was 1.9 per cent (95% CI 0.8-3.0).

Porcine Reproductive and Respiratory Syndrome Virus

Porcine reproductive and respiratory syndrome virus (PRRSv) was first confirmed in the UK in 1991 and is now considered endemic. In 2003/2004, a cross-sectional study of 103 British pigs found  that 35 herds (34.0 per cent ) were seronegative, 41 (39.8 per cent) were seropositive and 27 (26.2 per cent) were vaccinated.

A more recent study by Velasova et al. (2012) estimated that there was active PRRSv circulation on 35.1 per cent of farms.

PRRSv is not zoonotic. However, the economic impact of this disease to pig farming is significant with direct and indirect costs associated with production losses, increased mortality, treatment, and disruption to breeding programmes.

  • A total of 621 plasma samples, from 621 pigs, were tested for antibodies to PRRSv.
  • After accounting for clustering of pigs within farms the seroprevalence was 58.3 per cent (95% CI 53.1-63.4).
  • A total of 372 tonsil samples were tested for PRRS viral RNA.
  • After accounting for clustering of pigs within farms, the prevalence of PRRSv RNA-positive tonsils in these 372 samples was 8.3 per cent (95% CI 5.5-11.2).

Antimicrobial Resistance in Campylobacter coli

Campylobacter is a key area for public health targeting. The number of confirmed cases of human campylobacteriosis in the EU has shown a statistically significant increasing trend between 2008  and 2011.

Campylobacter jejuni and Campylobacter coli are the most common species to cause human infections, with approximately seven per cent of human infections caused by the latter in England and Wales. To date, studies indicate that the majority of infections are due to poultry, poultry handling or poultry products.

Directive 2003/99/EC, requires EU Member States to provide comparable monitoring data on the occurrence of antimicrobial resistance in zoonotic bacteria. The results of the antimicrobial resistance monitoring are assessed and reported in the annual EU Summary Report on Antimicrobial Resistance (available on the EFSA web site).

This study provided an opportunity to obtain C. coli isolates for AMR testing and reporting to the EU so as to comply with the harmonised requirements.

The method used was not the same as performed in previous studies.

  • Overall, 153 C. coli isolates were tested for their in vitro susceptibility to seven antimicrobials.
  • The greatest levels of resistance were observed against tetracyclines (77.8 per cent) and streptomycin (66.0 per cent). There was also a moderate level of resistance against erythromycin (27.5 per cent), nalidixic acid (17.0 per cent) and ciprofloxacin (12.4 per cent). No resistance was observed against either chloramphenicol or gentamicin.

Extended Spectrum Beta Lactamase (ESBL) E. coli

The monitoring and reporting of AMR data from Escherichia coli within the EU is encouraged but voluntary.

The emergence of E. coli with resistance to extended spectrum β-lactam antibiotics (ESBLs) has been reported in farm animals both in the UK and other countries such as Belgium, China, France and The Netherlands. Farm animals can harbour different types of ESBL, carried by various bacteria including E. coli, although the CTX-M types are currently usually the most prevalent ESBL gene type.

CTX enzymes confer resistance to beta-lactam antibiotics such as amoxicillin, but also to beta-lactam antibiotics that are 3rd and 4th generation cephalosporins, such as cefotaxime, ceftazidime and cefquinome. As cephalosporin antibiotics are important front-line antibiotics for use in humans, development or resistance in animals to these antibiotics is of concern.

  • A total of 637 caecal samples, from 637 pigs, were tested for ESBL E. coli.
  • After accounting for clustering within farms the overall prevalence of ESBL E. coli was 23.4 per cent (95% CI 19.2-27.6).

March 2014

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