Risk factors associated with introduction of wild-type porcine reproductive and respiratory syndrome (PRRS) virus into growing pigs in the Midwestern U.S.

Porcine reproductive and respiratory syndrome virus (PRRSV) infections in growing pigs are common and costly. We evaluated risk factors related to production practices and herd characteristics associated to wild-type PRRSV (WT-PRRSV) introduction into 63 wean-to-finish (WTF) herds through the implementation of surveys, active recording of activities and monthly oral fluid sampling during the growing phase. Herds were located in the Midwest region of the USA and observed prospectively. Logistic regression analysis of risk factors indicated that WTF herds that outsourced trucks for mortality removal (OR 7.08, p = 0.03) and herds with external maintenance crews (OR 7.14, p = 0.03) had higher risk of WT-PRRSV infections. These findings highlight the importance of mechanical transmission of PRRSV and the need to develop stricter biosecurity protocols in growing pigs. Overall, this study describes most common production management practices and characteristics of WTF sites, and potential risk factors that if addressed, can help improve biosecurity, control and elimination of PRRSV in growing pigs.