Pathogenesis in lambs and sequence analysis of putative virulence genes of Brazilian orf virus isolates

•We analysed the pathogenesis of four Brazilian orf virus isolates in lambs.•Sequences of three putative virulence genes were analyzed.•The amino acid identity among the isolates and reference strain was varied.•The identity of genes VEGF e IL-10v with other sequences was somehow correlated with the virulence in vivo.

The parapoxvirus orf virus (ORFV) is the agent of contagious ecthyma, an ubiquitous mucocutaneous disease of sheep and goats that may present variable clinical presentations. We herein studied the pathogenesis of ORFV infection in lambs and analyzed three putative virulence genes of four Brazilian ORFV isolates. Lambs inoculated in the labial commissures with each ORFV isolate (n = 4, viral titer 105.6 TCID50/ml) developed classical orf lesions, characterized by a progressive course of erythema/macules, vesicles, pustules and proliferative scabs. Lesions lasted an average of 22.9 days (18-26) and virus shedding was detected for approximately 24.6 days (18-30). Two isolates (SV269/11 and SV820/10) produced more severe, long-lasting lesions resulting in highest clinical scores. Lambs inoculated with isolate SV581/11 developed lesions markedly milder (lower clinical scores [p < 0.05]) and more limited than the other groups. Virus shedding by SV581/11 group, however, lasted similarly or even longer than the other groups. Sequence analysis of three virulence genes (VEGF, VIR and IL-10v) revealed amino acid deletions and mutations in VEGF and IL-10v genes of SV581/11 and SV252/11, the isolate(s) producing milder lesions. Additionally, the VEGF gene of isolate SV581/11 presented the lowest amino acid identity with the other isolates and with ORFV standard strain OV-IA82. Thus, these results demonstrate that ORFV isolates may display differential virulence in lambs and these differences might be associated with genetic changes in putative virulence genes.