Submitted to: Journal of Veterinary Diagnostic Investigation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/30/1995
Publication Date: N/A
Interpretive Summary: Porcine reproductive and respiratory syndrome (PRRS) is a virus-induced disease that causes significant financial loss for the United States swine industry. To reduce the financial impact of the disease, its spread must be minimized and this depends largely on a quick and accurate diagnosis. In general, the best way to make a diagnosis of any virus-induced disease is to isolate the causative virus from the infected animal. However, in the case of PRRS, the virus is sometimes difficult to isolate because it is very unstable and is quickly destroyed, especially if the infected pig dies before samples can be collected for testing. We have therefore looked at an alternative method of diagnosis for cases of reproductive failure associated with PRRS virus infection. Namely, we have looked for lesions, i.e. changes in body tissues, that may be unique for this disease and that persist even when the virus can no longer be identified. Our results suggest that such lesions may be present in the umbilical cord of affected fetuses and newborn pigs. We believe that the presence of these umbilical lesions are highly suggestive of PRRS virus infection.
Technical Abstract: Diagnosis of porcine reproductive and respiratory syndrome (PRRS) virus- induced reproductive failure in swine is difficult because of the rapid inactivation of virus in fetuses that have died prior to abortion or farrowing. In this report, we describe gross and microscopic lesions of diagnostic value found in fetuses transplacentally infected with PRRS virus (PRRSV) during late gestation. Seven sows free of PRRSV-specific antibody and one sow (#8) that had been previously infected with PRRSV were oronasally exposed to a PRRSV inoculum at or about 90 days of gestation (DG). One control sow (#9) was oronasally exposed to a sham inoculum at 90 DG. Sows were euthanized 21 days-post-exposure and fetuses were tested for virus. Transplacental infection and umbilical cord lesions were found in litters 1 through 7; however, no infection or lesions were found in litters 8 and 9. The gross lesions in the umbilical cords ranged from segmental hemorrhagic areas 1 to 2 cm in length to a full length involvement of the cord which was grossly distended with frank hemorrhage. All live fetuses that had gross lesions in their umbilical cord were viremic and a necrotizing arteritis with periarterial hemorrhage was found in each cord by histopathological examination. This was the most consistent microscopic lesion in fetuses infected with PRRSV. Sows 1 through 7 had endometritis and myometritis of varying degrees suggesting PRRSV may induce these lesions as well. This study indicates careful gross and microscopic examination of the umbilical cord may aid in the diagnosis of PRRSV-induced reproductive failure.