Evaluation of the persistence of porcine reproductive and respiratory syndrome virus in pig carcases

Laboratoire d'Hygiene Veterinaire et Alimentaire, Agriculture Canada, St-Hyacinthe, Quebec, Canada.

The presence of porcine reproductive and respiratory syndrome (PRRS) virus in pig meat was assessed in samples collected from experimentally infected pigs and from the carcases of pigs from infected herds at an abattoir. In the experimental study, pigs approximately six months old were inoculated with two isolates of PRRS virus and tissue samples were collected seven and 14 days after inoculation. At seven days, PRRS virus was recovered from lungs, tonsils, lymph nodes and muscle tissues, and viral antigens were detected by immunogold silver staining (IGSS) in formalin-fixed lungs, tonsils and scattered cells in muscle tissues. Neither PRRS virus nor antigens were detected in muscle tissue samples collected 14 days after inoculation. In the abattoir pigs, attempts were made to isolate PRRS virus from a total of 44 samples of muscle tissue, collected as pools, from the carcases of 44 pigs originating from seropositive herds. No PRRS virus could be isolated on porcine alveolar macrophages from these 44 muscle tissue samples and no PRRS virus antigens could be detected by IGSS in the formalin-fixed tissue samples. Although the results of experimental infections indicated that PRRS virus may be recovered from muscle tissues early after infection with the virus, the presence of PRRS virus in muscle tissues from carcases of slaughter pigs previously exposed to the PRRS virus could not be demonstrated.