Outbreaks of porcine reproductive failure: Report on a collaborative field investigation

Abstract

During the latter half of 1996, a series of abortion outbreaks occurred, primarily in southeast Iowa, with a clinical picture similar to Porcine Reproductive and Respiratory Syndrome (PRRS) in a naïve herd. After initial foreign animal disease investigations proved negative, a collaborative case-control study was designed. Its objectives were to describe these cases of intense reproductive failure; attempt isolation of viral agent(s), particularly postulated variant strains of PRRS virus; and identify potentialmanagement risk factors. Eligible case herds were those experiencing a current outbreak of abortion and submitting samples to one of the seven participating diagnostic laboratories. Control herds were randomly selected by the investigating veterinary medical officer from a list generated by the referring practitioner. For both case and control herds, sow blood samples and fetal tissues were collected for PRRSV serologyand multiple virus isolations, and management data were statistically analyzed to identify potential risk factors. Seventeen case and 34 control herds were enrolled between June 25, 1997 and November 10, 1998. The PRRS virus was isolated from seven cases and one control operation.Sow sera were PRRS positive on 87% of case premises and 55.7% of control premises. These results suggest that the swine abortion outbreaks beginning in 1996 were more likely due to PRRS virus than to an emerging disease. The US pork industry is vulnerable to emerging diseases, and needs to develop rapid capabilities for recognizing new infections and novel pathogens and strategies for detecting and controlling emerging diseases.