Transmission of porcine reproductive and respiratory syndrome virus from persistently infected sows to contact controls

The objective of this study was to determine if porcine reproductive and re spiratory syndrome virus (PRRSV) could persist in non-pregnant sows and if persistently infected sows could transmit virus to naive contact controls. Twelve PRRSV-naive, non-pregnant sows (index sows) were infected with a fie ld isolate of PRRSV and housed in individual isolation rooms for 42 to 56 d ays postinfection. Following this period, 1 naive contact sow was placed in each room divided by a gate allowing nose-to-nose contact with a single in dex sow. Index sows were not viremic at the time of contact sow entry. Viru s nucleic acid was detected by polymerase chain reaction, and infectious vi rus was detected by virus isolation in sera from 3 of the 12 contact sows a t 49, 56, and 86 days postinfection. All 3 infected contacts developed PRRS V antibodies. Virus nucleic acid was detected in tissues of all of the 12 i ndex sows at 72 or 86 days postinfection. Nucleic acid sequencing indicated that representative samples from index and infected contacts were homologo us (> 99%) to the PRRSV used to infect index sows at the onset of the study . This study demonstrates that PRRSV can persist in sows and that persisten tly infected sows can transmit virus to naive contact animals.