Porcine reproductive and respiratory syndrome outbreak in a confinement swine operation

Abstract

Sows at an established, mid-Western, 1,250 sow farrow to finish, confinement swine operation had a sudden onset of abortions and were lethargic and off-feed on July 1, 2010. The disease, Porcine Reproductive and Respiratory Syndrome (PRRS), was suspected based on the sudden onset of clinical signs consistent with infection in a naive herd. Before the outbreak, regular serological monitoring of the sow herd for PRRSV every three months yielded negative results. On examination, clinical findings: in the sows, included abortions with mummies, stillbirths and weak piglets, lethargy and off-feed; in the piglets and nursey pigs, pneumonia and generalized lymphadenopathy. ELISA for serum antibody and PCR for serum antigen detection were used for diagnosis of PRRSV infection. At the onset of clinical signs, ELISA testing results were negative but PCR assays were positive, which confirmed an acute outbreak because the pigs were positive for viral antigens but seronegative for PRRSV antibodies. To control the outbreak, all piglets were moved off site as soon as they were weaned. During the first month, there was a 50% mortality rate in the nursery pigs and a 30% abortion rate among the gilts and sows. For gilts and sows that remained at the original location, autogenous killed vaccine was prepared and given intramuscularly and intranasally. To evaluate the progess of the herd outbreak, piglets at the off-site location were monitored by PCR assay for the presence of virus in serum, which eventually became negative by September. Seronegative gilts were also put into the original herd, which was used as a tool to monitor for persistence of the virus. By September, abortion rates were about back to the pre-outbreak levels, and the piglets remained healthy at birth. In retrospect, a PRRSV risk assessment conducted every 2 years before the outbreak concluded that the farm was at risk of a PRRSV outbreak because of certain gaps in biosecurity. This included a lack of routine cleaning and disinfection of trucks that were used for transporting pigs to market and outside farms. However, no changes were instituted at that time. It is possible that a change in protocol would have prevented this outbreak.