Three novel canine papillomaviruses support taxonomic clade formation.

More than 100 human papillomaviruses (HPVs) have been identified and had their whole genomes sequenced. Most of these HPVs can be classified into three distinct genera, the alpha-, beta- and gamma-papillomaviruses (PVs). Of note, only one or a small number of PVs have been identified for each individual animal species. However, four canine PVs (CPVs) (COPV, CPV2, CPV3 and CPV4) have been described and their entire genomic sequences have been published. Based on their sequence similarities, they belong to three distinct clades. In the present study, circular viral DNA was amplified from three dogs showing signs of pigmented plaques, endophytic papilloma or in situ squamous cell carcinoma. Analysis of the DNA sequences suggested that these are three novel viruses (CPV5, CPV6 and CPV7) whose genomes comprise all the conserved sequence elements of known PVs. The genomes of these seven CPVs were compared in order properly classify them. Interestingly, phylogenetic analyses, as well as pairwise sequence alignments of the putative amino acid sequences, revealed that CPV5 grouped well with CPV3 and CPV4, whereas CPV7 grouped with CPV2 but neither group fitted with other classified PVs. However, CPV6 grouped with COPV, a lambda-PV. Based on this evidence, allocation of CPVs into three distinct clades could therefore be supported. Thus, similar to HPVs, it might be that the known and currently unknown CPVs are related and form just a few clades or genera.