Evaluation of the presence of porcine reproductive and respiratory syndrome virus in pig meat and experimental transmission following oral exposure.

A study was performed to evaluate the presence of porcine reproductive and respiratory syndrome virus (PRRSV) in pig meat collected at slaughterhouses and its potential transmission to pigs via pig meat. A total of 1039 blood samples were collected from pigs upon their arrival at the abattoir. The following day, meat samples (n = 1027) were collected from the carcasses of these same pigs. Samples originated from 2 Canadian slaughterhouses, 1 situated in the province of Quebec and the other situated in the province of Manitoba. Serum samples were tested for antibodies to PRRSV and both serum and meat samples were also tested for PRRSV nucleic acid by polymerase chain reaction (PCR). Seropositivity to PRRSV for all serum samples was 74.3%. Furthermore 45 (4.3%) of the total serum samples and 19 (1.9%) of the 1027 meat samples were positive for PRRSV by PCR. Sequence analysis of open reading frame (ORF) 5 performed on 15 of the 19 PRRSV strains identified in pig meat indicated that 9 were field strains and 6 were vaccine-like (98% to 99.7% nucleotide homology with the Ingelvac RespPRRS/Repro vaccine). One of these 6 strains presented an intermediate 2-6-2 restriction fragment length polymorphism (RFLP) cut pattern and the others showed the characteristic 2-5-2 RFLP pattern of the vaccine strain. All strains sequenced were determined to be North American strains. In only 1 of the 19 PRRSV-positive meat samples could PRRSV be isolated. To test the potential infectivity of meat samples containing residual PRRSV, 11 of the PCR-positive meat samples (weighing 1.05 to 1.8 kg) were each used in feeding experiments of 2 PRRSV antibody-negative specific pathogen-free pigs of 9 wk of age. Samples were cut into several pieces and fed to each pair of pigs on 2 consecutive days. Each pig pair was housed in a separate cubicle and serum samples were collected at -7, 0, 7, 14, and 20 to 21 days post exposure. Seven pig pairs were found to be infected by PRRSV following ingestion of meat samples, including meat samples containing vaccine-like virus, as judged by the demonstration of PRRSV antibodies and/or PRRSV nucleic acid in the serum. In summary, the present study indicated that low residual quantities of PRRSV may be found in a small percentage of pig meat collected at slaugtherhouses. Furthermore, when this meat was fed raw to pigs in the experimental setting designed, pigs could be infected by PRRSV.