Bovine papillomavirus
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 Bovine papillomavirus type 1 (3D reconstruction)
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Bovine papillomavirus (BPV) is a group of DNA viruses of the family Papillomaviridae that are highly prevalent in cattle, causing warts (papillomas and fibropapillomas) of the skin and alimentary tract, and more rarely cancers of the alimentary tract and urinary bladder.
BPV provides an excellent model for studying papillomavirus molecular biology, and also allows the dissection of the processes by which this group of viruses can cause cancer.
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[edit] Structure and genetic organisation
Like other papillomaviruses, BPVs are small non-enveloped viruses showing icosahedral symmetry. All BPVs have a circular double-stranded DNA genome. The genetic organisation of those BPVs which have been sequenced is broadly similar to other papillomaviruses. The open reading frames (ORFs) are all located on one strand, and are divided into early and late regions. The early region encodes nonstructural proteins E1 to E8. E5 (and the similar E8), E6, E7 are all oncoproteins. The late region encodes structural proteins L1 and L2. There is also a non-coding long control region (LCR).
[edit] Types
Six types of BPV have been identified, BPV-1 to BPV-6, which are divided into two broad subgroups, A and B.
Subgroup A viruses, including types 1, 2 and 5, have a genome of around 7.9 kb. BPV-1 and 2 are classified into Deltapapillomavirus, along with similar papillomaviruses of ungulates (eg deer papillomavirus, European elk papillomavirus, ovine papillomavirus 1,2); BPV-5 is classified into Epsilonpapillomavirus. Like all members of the papillomavirus class, these viruses infect only keratinocytes (epithelial cells); however, unlike other papillomaviruses, they cause proliferation of both keratinocytes and fibroblasts, causing benign fibropapillomas involving both the epithelium and the underlying dermis. The specificity of the types differs:
- BPV-1 infects paragenital areas
- BPV-2 infects skin, alimentary canal and urinary bladder
- BPV-5 infects teats and udders
Subgroup B viruses, including types 3, 4 and 6, have a smaller genome of around 7.3 kb. Thay are classifed as Xipapillomavirus. They infect keratinocytes (epithelial cells), causing pure papillomas involving only the epithelium. The specificity of the types differs:
- BPV-3 infects skin
- BPV-4 infects the upper alimentary tract
- BPV-6 infects teats and udders
[edit] Pathology
BPV is highly prevalent, with around 50% of cattle being estimated to bear lesions in the UK.[1] Cutaneous warts are most common in younger animals (under 2 years) and usually spontaneously regress due to the animal's immune response without significant scarring. The duration of infection is very variable (from one month to over a year) and recurrence is possible.[2]
Warts caused by subgroup B viruses have a cauliflower-like appearance and can attain the size of a fist; most common on the head, neck and shoulders, they may also occur in other locations.[2] Cutaneous fibropapillomas caused by subgroup A viruses have a nodular appearance.[2] Although unsightly, most skin warts rarely cause problems except in show animals. However, large warts may bleed, potentially leading to secondary infections, and florid warts of the teat can cause mastitis and interfere with suckling and milking. Fibropapillomas can be troublesome when present in the genital area, causing pain and interfering with calving.[2]
Warts contain large amounts of infectious virus which is relatively stable. Transmission between animals is common via, for example, fence posts or halters. Warts on the teats of lactating cows are readily transmitted to calves via abrasions. Contaminated tattooing or tagging equipment is another common source of infection.
[edit] Association with cancer
BPV-4 causes squamous cell carcinomas of the alimentary tract and BPV-2 cancers of the urinary bladder, in both cases in animals that have fed on bracken (Pteridium aquilinum). Bracken contains several immunosuppressants and mutagens and acts as a cofactor.[3]
BPV-1 and BPV-2 can also induce sarcomas and fibrosarcomas in other mammals, including horses (equine sarcoid)[4] and, experimentally, rabbits, hamsters and mice[5] (and reviewed in[6]).
[edit] Vaccines
Vaccines against BPV-2 and BPV-4 have been developed in the laboratory of M. Saveria Campo.[1]
[edit] References
- ^ a b Campo MS (1995) Infection by bovine papillomavirus and prospects for vaccination. Trends Microbiol. 3: 92-97
- ^ a b c d Merck Veterinary Manual
- ^ Jarrett WF, McNeil PE, Grimshaw WT et al. High incidence area of cattle cancer with a possible interaction between an environmental carcinogen and a papilloma virus. Nature (1978) 274:215-217
- ^ Chambers G, Ellsmore VA, O'Brien PM et al. Association of bovine papillomavirus with the equine sarcoid. J Gen Virol (2003) 84:1055-1062
- ^ Boiron, M, Levy, JP, Thomas, M, Friedmann, JC and Bernard, J. (1964) "Some properties of bovine papilloma virus." Nature 201:423. PMID 14110027
- ^ Shah KV, Howley PM. 'Papillomaviruses' in Fields Virology (3rd edn) (Fields BN, Knipe DM, Howley PM, et al., eds), Lippincott-Raven Publishers, Philadelphia, 1996
