Prevalence of Salmonella, Toxoplasma, Yersinia, Hepatitis E and Porcine Reproductive and Respiratory Syndrome virus in UK pigs at slaughter

Abstract

In 2006/7 the prevalence of Salmonella in UK slaughter pigs was found to be amongst the highest in Europe. In advance of the anticipated EU-wide National Control Programme for Salmonella in pigs, a UK-wide monitoring programme was set up by Defra and funded in collaboration with key Government and industry partners. The monitoring programme presented a cost-effective opportunity to concurrently collect data on other potentially zoonotic pathogens for which prevalence data is currently limited, including Toxoplasma, Yersinia, Hepatitis E virus (HEV) and Porcine Reproductive and Respiratory Syndrome virus (PRRSv). Antimicrobial resistance testing of Campylobacter coli isolates and testing for ESBL E. coli was also undertaken (details not reported here). This study will meet urgent evidence needs and improve our knowledge regarding potential risks to public health in the pig meat supply chain. Between January and April 2013, 600 slaughter pigs from 14 abattoirs throughout the UK were sampled. Sampling was weighted according to abattoir throughput. Sampling dates and pig carcasses were randomly allocated utilising the abattoir daily throughput as a sampling frame. Samples collected from each pig include a post-stun rectal swab (Salmonella), post-bleed serum samples (Toxoplasma, HEV and PRRSv), the caecum (Salmonella) and tonsils (Yersinia and PRRSv) at the evisceration point, and pre-chill carcase swabs (Salmonella and Yersinia). Salmonella isolation (ISO 6579), serotyping and phage typing, and the isolation of Yersinia, were undertaken at AHVLA. Plasma samples were tested by ELISA for antibodies to Toxoplasma (at the Toxoplasma Reference Unit), HEV (at Public Health England (PHE)) and PRRSv (at AHVLA), and also tested for HEV RNA (at PHE). Tonsil material from PRRSvseropositive pigs was tested by PCR and used for virus sequencing (at AHVLA). Introduction Foodborne diseases are estimated to cost the UK nearly £1.5 billion per year (FSA, 2011). Salmonella is the second most common foodborne zoonosis, with 9,455 laboratory-confirmed cases in the UK in 2011 (EFSA, 2013). Control of Salmonella in the EU has thus far focused predominantly on poultry, with Salmonella National Control Programmes (NCPs) having been implemented in the various chicken and turkey sectors from 2007 (Defra, 2011). The success of the NCPs in poultry has resulted in a progressive reduction in the number of cases in people. However, the proportion of human cases attributed to pork and pork products appears to be rising. In 2006/7, an EU baseline survey was conducted to assess the prevalence of Salmonella in pigs at slaughter (Commission Decision 2006/668). Levels in the UK were above the EU average; 40.4% (259/641) of pigs had evidence of current infection and/ or carcase contamination, with Salmonella isolated from 21.8% of lymph node samples, 15.1% of carcase swabs and 21.9% of caecal samples. A NCP for Salmonella in pigs is expected to commence in 2015 and reduction targets based on the EU mean prevalence are likely to be challenging for the UK pig industry. Since the last survey, efforts continued to reduce the prevalence of Salmonella in pigs. Therefore, a new monitoring programme to reassess the prevalence of infection was proposed. This presented an opportunity to simultaneously gather national-level prevalence data on other organisms to address additional knowledge gaps. In a recent EFSA Opinion on pig meat inspection, Toxoplasma gondii was identified as one of the most significant foodborne public health hazards (EFSA, 2011). There are an estimated 350,000 toxoplasmosis cases in the UK each year, of which 10-20% are symptomatic (ACMSF, 2012). Despite pig meat being considered a high risk food for transmission, a recent report from the Advisory Committee on the Microbiological Safety of Food (ACMSF) noted that there is virtually no data concerning the prevalence in UK livestock (ACMSF, 2012). In the EFSA Opinion, Yersinia was also deemed very important (EFSA, 2011). Yersiniosis was the fourth most frequently reported zoonosis in the EU in 2011 and infections are often acquired from raw or undercooked pig meat (EFSA, 2013). Consequently, EU