Summary. -Antigenic and genetic typing of pestiviruses isolated from Indian sheep and goats was carried out. testing of 1777 sheep and 1026 goat blood samples collected between 2004 and 2008 resulted in isolation of twelve pestiviruses, seven from sheep and five from goats. All of them were antigenically typed as bovine viral diarrhea virus 1 (BvDv-1). Both the partial 5ʹ-utr and entire non-structural autoprotease (n pro ) gene of the pestiviruses were amplified by rt-Pcr and sequenced. The phylogenetic analysis confirmed all twelve sheep and goat pestiviruses as BvDv-1 and they were further classified into two subtypes, BvDv-1b (seven) and . This is for the first time that BvDv-1c was detected in sheep and goats. however, no association between the subtype and geographic area of origin was observed. Although closely related, BvDv-1b and BvDv-1c isolates of sheep and goats were placed in a different clade than previously reported Indian BvDv-1b/ BvDv-1c isolates. This study confirmed widespread prevalence of BvDv-1 in Indian sheep and goats that has significance in the epidemiology of bovine viral diarrhea.Keywords: bovine viral diarrhea virus; BvDv-1; goat; n pro ; genetic typing; sheep; 5ʹ-utr e-mail: mishranir@rediffmail.com; phone: +91-755-2759204. Abbreviations: BD = border disease; BDv = BD virus; BvDv = bovine viral diarrhea viruses; BvDv-1,2 = bovine viral diarrhea virus 1 and 2; IPMA = indirect immunoperoxidase monolayer assay; MAb(s) = monoclonal antibody(ies); ncp = non-cytopathic; n pro = non-structural autoprotease; SFtr = sheep fetal thymus cells
Bovine viral diarrhoea virus (BVDV) is an economically important pathogen of cattle and sheep belonging to the genus Pestivirus of the family Flaviviridae. Although the BVDV non-structural N-terminal protease (N(pro)) acts as an interferon antagonist and subverts the host innate immunity, little is known about its immunogenicity. Hence, we expressed a recombinant BVDV N(pro)-His fusion protein (28 kDa) in E. coli and determined the humoral immune response generated by it in rabbits. The antigenicity of the N(pro) protein was confirmed by western blot using anti-BVDV hyperimmune cattle, sheep and goat serum, and anti-N(pro) rabbit serum. When rabbits were immunized with the N(pro) protein, a humoral immune response was evident by 4 weeks and persisted till 10 weeks post immunization as detected by ELISA and western blot. Despite N(pro)-specific antibodies remaining undetectable in 80 serum samples from BVDV-infected sheep and goats, BVDV hyperimmune sera along with some of the field cattle, sheep and goat sera with high BVDV neutralizing antibody titres were found positive for N(pro) antibodies. Our results provide evidence that despite the low immunogenicity of the BVDV N(pro) protein, a humoral immune response is induced in cattle, sheep and goats only with repeated BVDV exposure.
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