Regeneration and characterization of a recombinant bovine viral diarrhea virus and determination of its efficacy to cross the bovine placenta.

The capacity of different bovine viral diarrhea virus (BVDV) strains to cause transplacental infection is variable. BVDV strain SD-1 was isolated from a persistently infected heifer. Its genome represents the only reported nucleotide sequence of a noncytopathic viral isolate determined without cell culture passage in the laboratory. Thus, SD-1 might possess biological advantages over other NCP BVDV strains to be used as a model virus for investigation of viral transplacental transmission. To evaluate if a molecularly generated BVDV SD-1 is capable of crossing the bovine placenta efficiently, a full-length cDNA clone of SD-1 was constructed using RT-PCR amplification and standard molecular techniques. In vitro transcripts synthesized from the cDNA template directed the generation of infectious virus in MDBK cells with a transfection efficiency as high as 4.7 x 10(5) FFU/mug RNA. The recovered virus termed ASD1 harbored five silent point mutations engineered as genetic markers and was similar to wild type (wt) SD-1 in viral growth kinetics. As evaluated in the pregnant heifers, ASD1 was capable of crossing the bovine placenta efficiently, suggesting that NCP BVDV SD-1 is a suitable viral backbone for investigation of the role of viral genetic element(s) in viral transplacental transmission by allowing for evaluation of newly created viral mutants.