Molecular characterization of bovine viral diarrhea virus type 2 isolate originating from a native Indian sheep (Ovies aries)

The wide spread prevalence of bovine viral diarrhea virus type 1 (BVDV-1) in cattle and recent identification of BVDV-2 in goats in India warranted pestivirus surveillance in sheep. Nested reverse transcription-polymerase chain reaction (RT-PCR) was used to detect BVDV-2 in one of 1561 blood samples collected randomly from 78 sheep flocks in 11 states of India. Antigenic characterization of the isolated pestivirus using polyclonal and monoclonal antibodies typed the isolate as BVDV-2. When analyzed at genetic level in Npro (N-terminal autoprotease) and entire gene region coding structural proteins, namely capsid (C) protein and envelope proteins Erns (ribonuclease secreted), E1 and E2 genomic organization was the same for all pestiviruses, the nucleic acid and amino acid sequences showed highest similarity with those of BVDV-2. When compared with BVDV-2 isolate 890, the sequence homology was 83.7% for C, 84.6% for Erns and E1, and 81.5% for E2. The cleavage site C/Erns was found totally conserved while Npro/C was conserved only from C-terminus of Npro, Erns/E1 site was conserved only from C-terminus of Erns and E1/E2 site was conserved only from C-terminus of E1. Phylogenetic analysis of nucleotide sequences in 5′ untranslated regions (UTR), Npro, E2, NS3 and NS5B regions placed the sheep isolate in a separate clade within BVDV-2 subtype b. This was supported by the presence of unique mutations in the structural protein coding regions beside NS3 and NS5B. To our knowledge this is the first report on the sequence analysis of the entire structural gene coding region of a BVDV-2b isolate. This is also the first occurrence of BVDV-2 subtype b in sheep, providing the evidence that this subtype can also occur in species other than cattle.