Viral and squamous papillomas in captive polar bears (Ursus maritimus)

Papillomas, many of which are virally induced, are common proliferative cutaneous and mucocutaneous lesions in multiple species, exhibiting characteristic histologic cytopathic changes that distinguish them from nonviral squamous papillomas. A single case report of a novel papillomavirus, Ursus maritimus papillomavirus-type 1, in a polar bear has been reported without investigation into any association between this virus and papilloma formation. We identified papillomas in 3 polar bears. All 3 cases had pedunculated masses consistent with papillomas (i.e., proliferative epithelium forming papillary projections on a fibrovascular stalk); case 1 also exhibited koilocytosis (cytopathic change), consistent with a viral papilloma. Polymerase chain reaction (PCR) using primers that can amplify a diversity of papillomaviruses followed by amplicon sequencing yielded a novel papillomavirus sequence in case 1, which shared <70% nucleotide identity to any known papillomavirus type, indicative of a putatively novel papillomavirus. In situ hybridization (ISH) of case 1 demonstrated viral nucleic acid within proliferative cells and not within the adjacent normal skin, suggesting the virus was the causative agent of this papilloma. The squamous papillomas in cases 2 and 3 were negative for papillomavirus by both PCR and ISH. These findings support our hypothesis that cytopathic effect is associated with the presence of papillomavirus in polar bears, while the lack of histologic cytopathic change may predict nonviral pathogenesis. Further sequencing of the putatively novel viral genome will benefit research and conservation efforts of polar bears.