GROSS AND MICROSCOPIC LESIONS IN PORCINE FETUSES INFECTED WITH PORCINE REPRODUCTIVE AND RESPIRATORY SYNDROME VIRUS

Diagnosis of porcine reproductive and respiratory syndrome virus (PRRS V)-induced reproductive failure in swine is difficult because of the r apid inactivation of virus in fetuses that have died prior to abortion or farrowing. In this report, we describe gross and microscopic lesio ns of diagnostic value found in fetuses transplacentally infected with PRRSV during late gestation. Seven sows free of PRRSV-specific antibo dy and 1 sow (#8) that had been previously infected with PRRSV were or onasally exposed to a PRRSV inoculum at or about 90 days of gestation (DG). One control sow (#9) was oronasally exposed to a sham inoculum a t 90 DG. Sows were euthanized 21 days postexposure, and fetuses were t ested for virus. Transplacental infection was detected in litters 1-7, and gross lesions of the umbilical cord were observed in some fetuses in 6 of the 7 litters. No transplacental infection or fetal lesions w ere found in litters 8 and 9. The gross lesions in the umbilical cords ranged from segmental hemorrhagic areas 1-2 cm in length to a full le ngth involvement of the cord, which was grossly distended with frank h emorrhage. All live fetuses that had gross lesions in the umbilical co rd were viremic, and histopathologic examination revealed a necrotizin g umbilical arteritis with periarterial hemorrhage. This was the most consistent microscopic lesion in fetuses infected with PRRSV. Sows 1-7 had endometritis and myometritis of various degrees, suggesting PRRSV also may induce these lesions. Careful gross and microscopic examinat ion of the umbilical cord may aid in the diagnosis of PRRSV-induced re productive failure.