Circulation of orf viruses containing the NZ7-like vascular endothelial growth factor (VEGF-E) gene type in India

Orf, a poxviral skin infection of small ruminants is caused by orf virus (ORFV) of the genus Parapoxvirus of the Poxviridae family. Vascular endothelial growth factor (VEGF) is an important virulence factor that is responsible for proliferative lesions in parapoxviral infections. VEGF gene shows high intra- and inter-species variability. Two variants of VEGF have been described globally in ORFV, viz. NZ2- and NZ7-like. In the present study, ORFV isolates of different geographic regions of India were analysed on the basis of the VEGF gene. Indian ORFV isolates showed 95.7-100 % nucleotide (nt) and 78.4-99.3 % amino acid (aa) identity with each other, except ORFV-Assam/LK/14 and ORFV-Meghalaya/03 which shared 85.1-88.35 % and 79.1-81.8 % identity, at nt and aa levels, respectively with other Indian ORFV isolates. All Indian ORFVs under the study demonstrated 83.5-99.1 % nt and 80.5-97.9 % aa identity with NZ7-like VEGF as compared to 41.2-44.8 % nt and 30.7-38.4 % aa identity with NZ2-like VEGF on comparison with global ORFV strains. Phylogenetic analysis based on the VEGF gene showed two clusters of ORFV in which the Indian ORFVs clustered with NZ7-like VEGF from global ORFV strains, mostly from China. Despite the considerable variation, VEGF protein from Indian ORFV strains showed conserved VEGF homology domain with eight cysteine residues. Homology modeling of Indian ORFV strains predicted the presence of extended Loop 3 similar to NZ7-like VEGF. Therefore, the present study showed the circulation of ORFV strains with comparatively less variable NZ7-like VEGF in India which implicates its importance in the epidemiology of ORFV infections in the country.