Control of Salmonella infection in pigs at the farm level in Great Britain

Salmonella is an important zoonotic pathogen and 10,000 cases of human salmonellosis are reported annually in the UK. The most commonly implicated serovars are S. Enteritidis and S. Typhimurium. Since a quarter of British pigs carry Salmonella in their gut at slaughter, there is an urgent requirement for improved control strategies that could benefit human health. A literature review showed that hygiene, biosecurity and feed exposures were important risk factors for Salmonella infection in pigs, which originates from environmental contamination or introducing infected pigs into the herd. The aim of this research was to design and test an intervention to control Salmonella in pigs. The following objectives were achieved: 1. An evaluation of tests for Salmonella in pigs: isolation by culture and the meat juice (MJ) ELISA, to inform test selection for the intervention study. 2. A national farm-level survey to estimate the variation in Salmonella prevalence between farms and to investigate risk factors associated with infection. 3. An analysis of a merged MJ ELISA dataset with a quality assurance dataset to provide additional information on risk factors. 4. A randomised controlled trial of an enhanced hygiene and biosecurity protocol intended to control Salmonella infection in finisher pigs. The intervention was tested on 48 farms. The primary outcome was the pen incidence rate of Salmonella infection, measured by culture of pooled pen floor faecal samples. No important change in incidence between intervention and comparison groups was seen. Analysis by reported behaviour showed that improved attention to between-batch cleaning and disinfection was beneficial. The prevalence of infected pens shortly after re-stocking had an overwhelming effect on incidence whilst improved hygiene during production had relatively little effect. Therefore, enhanced hygiene and biosecurity may yield benefits in Salmonella control, but these may be overwhelmed by the introduction of infection at re-stocking or through residual environmental contamination.