An investigation into the efficacy of washing trucks following the transportation of pigs--a salmonella perspective.

Washing of trucks before leaving the abattoir is mandatory in the Republic of Ireland; however, little is known about the efficacy of the cleaning methods in use on trucks following the transportation of live pigs in Ireland. A National Salmonella Control Programme is in place in the Republic of Ireland, which requires the categorization of all pigs according to their Salmonella status. Herds in categories 1, 2, and 3 have a serological prevalence of infection with Salmonella serotypes of <or=10%, >10% to <or=50%, and >50% to <or=100%, respectively. Healthy pigs can carry Salmonella serotypes in their intestine, and the stress of transport may induce these carriers to shed the bacterium at a higher rate. Salmonella-contaminated trucks may infect other farms, abattoirs, and other animals if the trucks are not cleaned between trips. The main objective of this study was to determine the efficacy of washing trucks transporting pigs from category 1 and category 3 herds. In total, six category 3 and three category 1 herds were followed to three separate abattoirs. Salmonella organisms in samples collected from farm pens and from trucks preload, postload, and after washing were quantified and compared using serotyping, phage typing, and pulsed-field gel electrophoresis (PFGE). Enterobacteriaceae counts were also evaluated to indicate the level of contamination of the environment with enteric bacteria. Results suggest that although trucks are visually clean after cold-water power hosing, such washing is not effective at reducing levels of Enterobacteriaceae regardless of category. Of the 108 samples taken from trucks transporting category 3 herds, 6% were positive for Salmonella spp. preload, 17% postload, and 18% after washing. In contrast, of the 54 samples taken from trucks transporting the three category 1 herds, 11% were positive for Salmonella spp. preload, 11% postload, and 6% after washing. Salmonella isolates from the trucks postload and after washing were indistinguishable, based on PFGE patterns, from salmonellae isolated on farm, indicating the probable shedding by carrier pigs during transit. These results demonstrate the need for better cleaning of trucks after each load, particularly when transporting pigs from high-risk herds.