Identification and whole-genome characterization of a novel equine papillomavirus

Papillomaviruses (PVs) are small, non-enveloped viruses with double-stranded circular DNA genomes that infect a wide range of hosts, including mammals, birds, reptiles, and fish. While human papillomaviruses are extensively studied, recent advancements in high-throughput sequencing techniques have increased the detection and genetic characterization of PVs from various animal species. Here, we describe the identification and whole-genome characterization of a divergent equine papillomavirus (EcPV) detected through a viral metagenomic investigation of a horse in Denmark exhibiting neurological signs. Using Nanopore sequencing and Sanger sequencing, we assembled a complete viral genome of 7767 nucleotides. Phylogenetic analysis, based on concatenated E1, E2, L2, and L1 gene sequences, showed that the identified virus clustered within the same clade as EcPV3 (genus Dyoiotapapillomavirus) and EcPV6 (genus Dyorhopapillomavirus) but was situated on a distinct separate branch. Comparative genome analysis revealed approximately 52% nucleotide sequence similarity to EcPV3 and EcPV6, which share 66% similarity with each other. The L1 gene, commonly used for papillomavirus classification, exhibited a sequence identity to EcPV3 (58.4%) and EcPV6 (60.0%). The other viral genes displayed a 39-62% identity to the respective genes from EcPV3 and 6 further supporting the divergence of this newly identified PV. The combination of the phylogenetic analysis and the genetic divergence suggests that this newly identified papillomavirus may constitute a novel species or genus within the Papillomaviridae family. Our findings expand the known diversity of equine papillomaviruses and contribute valuable insights into their evolutionary relationships.