Molecular epidemiologic investigation of the role of gilts in the introduction and transmission of Salmonella in swine production systems.

摘要

Objective: To investigate whether purchased gilts introduce new Salmonella genotypes into a swine production system and acquire Salmonella infection from resident pigs. Materials and methods: One multi-site and one single-site swine production system from Illinois were recruited on prior evidence of a high prevalence of Salmonella infection. Cohorts of 102 and 120 incoming gilts on the multi-site and single-site farms, respectively, were sampled longitudinally for five to eight visits until the gilts were introduced into the breeding herd. On each visit, fecal and floor samples were obtained from cohort gilts and an approximately equal number of resident pigs in the same or adjacent room or building. All samples were cultured to detect Salmonella. The 123 Salmonella isolates were genotyped using repetitive sequence polymerase chain reaction with REP, BOX, and ERIC primers. Cluster analysis classified the isolates by degree of genetic relatedness. The 45 isolates from the multi-site farm were serotyped. Results: For both farms, the most closely genetically related Salmonella isolates were obtained from the same room on the same visit. For the multi-site farm, there was no evidence of transmission between gilts and resident pigs. For the single-site farm, there was evidence of transmission between gilts and resident pigs in the breeding barns. However, conclusive evidence that incoming gilts introduce new Salmonella genotypes into a swine production system was lacking. Serotyping information supported conclusions drawn from genotyping data. Implications: Spatial separation of purchased gilts from other pigs by all-in, all-out pig flow reduces Salmonella transmission in swine production systems.