Abstract
This study reports the in vivo and in vitro comparison of two pestivirus isolates, one of swine (87/6) and another of sheep origin (137/4). Both showed similar growth characteristics in vitro, and other features in common with most border disease virus (BDV) strains. It was hypothesized that, rather than being a strain of hog cholera virus (HCV), the swine isolate might be a "BDV-like virus" infecting pigs. Both viruses were inoculated into pregnant swine and sheep in order to: a) determine whether or not the swine isolate would infect the offspring in utero and b) to ascertain the congenital transmissibility of BDV to swine. Both viruses were able to cause transplacental infections in the two species. A variety of combinations of virus and antibody status were recorded in the fetuses, including some which revealed the concomitant presence of virus and antibody, suggesting the presence of circulating immune complexes. Pathological findings were compatible with previous reports of border disease in sheep. It was concluded that the swine isolate could not be distinguished from the BDV isolate 137/4 on the basis of their cell culture growth characteristics and ability to in- duce transplacental infections in both sheep and swine, or by the serological responses of infected animals. These findings provided evidence that the isolate 87/6 is a virus more closely related to BDV than to HCV, despite its origin from swine. Next, a fraction of the pestivirus genome coding for 86% of the core gene was prepared from both isolates using reverse transcription polymerase chain reaction. Amplified fragments were subsequently cloned, sequenced and compared with other pestivirus genomes. This provided further support for the hypothesis of the BDV-like nature of the swine isolate. It is suggested that the virus may have crossed the species barrier in nature. The present study shows that transplacental infections in swine with BDV-like viruses can occur.