Diagnostic investigation of chronic porcine reproductive and respiratory syndrome virus in a breeding herd of pigs

Forty-five sows and 15 boars were selected at random from a breeding herd k nown to be chronically infected with porcine reproductive and respiratory s yndrome virus (PRRSV) and lymphoid, immune-privileged, and non-lymphoid/non -immune-privileged tissues were tested for the presence of the virus by PCR , virus isolation, and immunohistochemistry. The virus was isolated from th e lateral retropharyngeal lymph node of one sow; the isolate was nucleic ac id sequenced and determined to be of field origin, and it was inoculated in to two PRRSV-naive pregnant sows (A and B) at 95 days of gestation. They we re necropsied 14 days later and samples of maternal and fetal tissue and bl ood samples were collected. Sow A had 10 fresh, six partially autolysed, an d two mummified fetuses, and sow B had six fresh and viable fetuses. Viral nucleic acid was detected by PCR in tissue pools from each sow and also fro m pooled fetal tissues, and the virus was isolated from fetal pools from so w A.