Molecular characterization of ovine pestiviruses

Forty-two ovine pestivirus isolates, collected over a period of 18 years, were compared by phylogenetic analysis. The viruses were mostly field isolates from Britain; two others originated from Sweden and two from New Zealand. RT-PCR products were obtained from two genomic regions, one within the 5'-noncoding (5'-NC) region, and the other encompassing parts of the p20 (Npro) and C coding regions. Direct sequencing of the 5'-NC PCR products, followed by computer-assisted phylogenetic analysis, divided the ovine pestiviruses into three main genotypes. The results demonstrated that sheep may naturally be infected not only with border disease virus (BDV), but also with bovine viral diarrhoea virus (BVDV) types I and II. The BDV isolates segregated into two principal subtypes represented by the Moredun strain from Scotland and the 137/4 strain from England. The BVDV-I group was composed of three clusters, two of them represented by BVDV reference strains NADL and Osloss, respectively, and the third by ovine isolates D1120/1 and D1432/P. The grouping of ovine pestiviruses, based on comparative nucleotide sequence analysis of the 5'-NC region, was confirmed by comparative analysis of the p20 (Npro) and C coding regions, performed both at the nucleotide and at the amino acid level. The presence of three genotypes in sheep, including BVDV-I and BVDV-II, indicates the inadequacy of the current hostspecies-based nomenclature and classification of pestiviruses.