Detection of bovine papillomavirus type 1 genomes and viral gene expression in equine inflammatory skin conditions.

Papillomaviruses are normally strictly species-specific and even under experimental conditions do not usually infect any other host than the natural host. The only documented reports of natural papillomavirus cross-species infection are of BPV-1/BPV-2, which can infect horses and induce equine sarcoids. BPV DNA has not been detected in non-sarcoid equine tumours or equine papillomas, but its presence has been reported in some cases of equine dermatitis. In the present study, we show that equine inflammatory skin conditions harbour episomal circular double stranded BPV-1 genomes, with copy numbers ranging from 0.2 to 155 copies/cell. BPV-1 E1, E2 and E5 genes were expressed in these inflammatory skin lesions, indicating active infection. We conclude that some cases of equine dermatitis are associated with the presence of circular, episomally maintained BPV-1 genomes that express viral transcripts.