Bovine papillomavirus (BPV), of the Papillomaviridae family, is a group of DNA viruses common in cattle. The virus can cause warts of the skin and alimentary tract and in rare cases cancer. It is also though that equine sarcoid, a skin tumor, is brought on in horses and donkeys by BPV.
BPV is a good model for the study of the papillomavirus molecular biology. Like others in their family BPVs are small non-enveloped viruses with an icosahedral capsid around 50-60 nm in diameter. BPVs have a circular double-stranded DNA genome. Six types of BPV have been characterized and are divided into three subgroups.
BPV 1 and 2, like all members of the papillomavirus class, these viruses only infect keratinocytes; however, they do cause proliferation of both keratinocytes and fibroblasts, causing benign fibropapillomas involving both the epithelium and the underlying dermis. BPV-3 infects the skin, while 4 infects the upper alimentary tract and 6 infects teats and udders. BPV-5 is a mix of the others and can cause both pure papillomas and fibropapillomas.
Around 50% of cattle in the UK are estimated to bear lesions. In younger animals cutaneous warts are most common and usually regress spontaneously due to the animals’ immune response. Infection can last from one month to over a year.
The warts caused by the virus have a cauliflower-like appearance and can vary in size and location. Small warts rarely cause any problems; however larger warts can bleed and potentially lead to secondary infection. For animals that are immunosuppressed papillomatosis in the upper gastrointestinal tract can lead to difficulties in eating and breathing.
Transmission of the virus is common when animals rub on fence posts or halters. The virus is also spread from contaminated tagging equipment. Cancers are common in locations where the grazing land is infected with bracken. Bracken contains several immunosuppressants and mutagens and consumption in large quantities leads to acute poisoning. Symptoms of this are bone marrow depletion and as a cancer cofactor at lower levels of consumption. These tumors form a model for some types of human oesophageal cancer and there is an association between exposure and consumption of bracken and risk of developing oesophageal cancer.