Characterization of Bovine papillomavirus 28 (BPV28) and a novel genotype BPV29 associated with vulval papillomas in cattle

Papillomavirus (PV) infections are associated with the development of cutaneous and mucosal tumors in humans and various animal species. In humans, infection of high-risk human PVs (HPVs) causes anogenital cancers, while in animals, anogenital-associated PVs are not well understood. Among animal PVs, Bos taurus PVs (BPVs) have the most diverse genotypes, up to 28 of them. The present study will report two unique BPVs identified in vulval papilloma lesions from two Holstein Friesian cattle by conventional PCR and sequencing. In the first case, BPV28 harboring two L1 open reading frames (ORFs) due to a five-nucleotide deletion was identified. In the second case, histologically diagnosed as papilloma, an unclassified BPV genotype was detected. However, in both cases, the immunohistochemistry against PV antigen was negative. The full genome of the unclassified BPV was amplified by inverse PCR and analyzed by genome-walking sequencing. The L1 nucleotide sequence was most identical to BPV genotype 6 (BPV6), showing 78 % identity, indicating that this novel BPV should be classified as species Xipapillomavirus 1, genotype BPV29. The mRNA expression of three early genes (E1, E2, E10), but not L1, was confirmed in both BPV28- and BPV29-detected papilloma lesions. The present study suggests the involvement of novel types of BPV in vulval papilloma. The alteration of BPV28 pathogenicity due to the frameshift mutation of L1 needs to be elucidated in the future.