Porcine Reproductive & Respiratory Syndrome (PRRS)

Porcine reproductive and respiratory syndrome (PRRS) was first reported in the USA in 1987. Since then, outbreaks of PRRS and successful isolation of the virus have been confirmed throughout North America, Asia, South America, Africa, and Europe. The etiologic agent of porcine reproductive and respiratory syndrome is a virus in the group Arteriviridae. The virus is enveloped and ranges in size from 45 to 80 mm. Inactivation is possible after treatment with ether or chloroform; however, the virus is very stable under freezing conditions, retaining its infectivity for 4 months at -70°C (-94°F). As the temperature rises, infectivity is reduced (15–20 minutes at 56°C [132.8°F]). After infection of a naive herd, exposure of all members of the breeding population is inconsistent, leading to development of naive, exposed, and persistently infected subpopulations of sows. This situation is exacerbated over time through the addition of improperly acclimated replacement gilts and leads to shedding of the virus from carrier animals to those that have not been previously exposed. The primary vector for transmission of the virus is the infected pig and contaminated semen. Controlled studies have indicated that infected swine may be long-term carriers, with adults able to shed PRRS virus for up to 86 days after infection, and weaned pigs able to harbor virus for 157 days. Experimentally infected boars can shed virus in the semen up to 93 days after infection.