Evaluation of airborne shedding of modified-live porcine reproductive and respiratory syndrome virus from growing pigs

Introduction Porcine reproductive and respiratory syndrome (PRRS) costs the US pork industry $1.8 million per day.1 Swine practitioners have been successful eliminating PRRS virus (PRRSv) from breeding herds by implementing herd closure-homogenization protocols.2 Implementation of these protocols has resulted in a source of PRRSv PCR-negative weaned pigs to be placed in growing facilities. A large proportion of these negative pigs are vaccinated with PRRS modifiedlive virus (MLV) vaccine since they are raised in high pig density areas where transmission of wild-type PRRSv from neighboring farms is a frequent event.3 Vaccination of these populations has shown to improve performance in the face of wild-type virus infections.4,5,6,7 However, some questions arise regarding the potential transmission of PRRS MLV from vaccinated to negative populations. The objectives of this study were to evaluate the magnitude and duration of airborne shedding of PRRS MLV vaccine from growing pigs under commercial conditions and to assess the ability of a basic biosecurity protocol to prevent PRRS MLV to be transmitted from vaccinated to nonvaccinated growing pigs raised in the same facility.