The Orthopoxvirus (OPV) genus of the Poxviridae family contains several human pathogens, including Vaccinia virus (VACV), which have been implicating in outbreaks of a zoonotic disease called Bovine Vaccinia in Brazil. So far, no approved treatment exists for OPV infections, but ST-246 and Cidofovir (CDV) are now in clinical development. Therefore, the objective of this work was to evaluate the susceptibility of five strains of Brazilian VACV (Br-VACV) to ST-246 and Cidofovir. The susceptibility of these strains to both drugs was evaluated by plaque reduction assay, extracellular virus's quantification in the presence of ST-246 and one-step growth curve in cells treated with CDV. Besides that, the ORFs F13L and E9L were sequenced for searching of polymorphisms associated with drug resistance. The effective concentration of 50% (EC₅₀) from both drugs varies significantly for different strains (from 0.0054 to 0.051 μM for ST-246 and from 27.14 to 61.23 μM for CDV). ST-246 strongly inhibits the production of extracellular virus for all isolates in concentrations as low as 0.1 μM and it was observed a relevant decrease of progeny production for all Br-VACV after CDV treatment. Sequencing of the F13L and E9L ORFs showed that Br-VACV do not present the polymorphism(s) associated with resistance to ST-246 and CDV. Taken together, our results showed that ST-246 and CDV are effective against diverse, wild VACV strains and that the susceptibility of Br-VACV to these drugs mirrored the phylogenetic split of these isolates into two groups. Thus, both ST-246 and CDV are of great interest as compounds to treat individuals during Bovine Vaccinia outbreaks in Brazil.

痘病毒科的正痘病毒(OPV) 属包含几种人类病原体，包括牛痘病毒（VACV），这一直牵涉在巴西爆发一种称为牛痘苗的人畜共患病。迄今为止，尚无针对 OPV 感染的获批治疗方法，但 ST-246 和西多福韦 (CDV) 目前正处于临床开发阶段。因此，这项工作的目的是评估五种巴西 VACV (Br-VACV) 对 ST-246 和西多福韦的敏感性。这些菌株对两种药物的敏感性通过噬菌斑减少试验、在 ST-246 存在下的细胞外病毒定量和用 CDV 处理的细胞中的一步生长曲线来评估。除此之外，对ORF F13L和E9L进行测序以寻找与耐药性相关的多态性。有效浓度50%（EC ₅₀) 对于不同菌株，两种药物的差异显着（ST-246 为 0.0054 至 0.051 μM，CDV 为 27.14 至 61.23 μM）。ST-246 强烈抑制浓度低至 0.1 μM 的所有分离株的细胞外病毒的产生，并且观察到 CDV 处理后所有 Br-VACV 的后代产生相关减少。F13L 和 E9L ORF 的测序表明 Br-VACV 不存在与对 ST-246 和 CDV 抗性相关的多态性。总之，我们的结果表明，ST-246 和 CDV 对多种野生 VACV 毒株有效，并且 Br-VACV 对这些药物的敏感性反映了这些分离株的系统发育分裂为两组。因此，ST-246 和 CDV 作为在巴西牛痘苗爆发期间治疗个体的化合物引起了极大的兴趣。