Papomaviridae
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Introduction
Papillomaviruses infect keratinized cells, giving rise to sarcoids, warts, and papillomas.
Morphology
- Medium-sized, icosahedral, non-enveloped dsDNA viruses
Virulence and Pathogenesis
- Target actively-dividing cells
- Warts: genes expressed are associated with transformation (hyperplasia and delayed maturation)
- Virus is shed as cells exfoliate
- Oral papillomas in young animals often resolve spontaneously
Epidemiology
- Resistant viruses: can persist in environment for months
- Restricted to stratified squamous and mucosal epithelia with slow growth
- Usually species specific
Types and Subtypes
Virus by Species
Canine Papillomavirus
- Occur in oropharynx of puppies aged 4-6 weeks
- Usually resolve spontaneously
Bovine Papillomaviruses
- 2 groups:
- Fibropapillomas: viral DNA sequences, but no virus found
- Epithelial Papillomas: virus found
- Calves most commonly affected
- Usually resolves spontaneously
- Can undergo malignant transformation to alimentary carcinomas
- Usually concurrent with grazing bracken (co-carcinogen) and ingesting quercetin (immunosuppressant)
- Can cause squamous cell carcinoma of the eye in Hereford cattle, where UV light acts as the co-carcinogen
Equine Papillomaviruses
- Occurs in horses aged 1-3 years
- Muzzle, oral cavity
- Spread by direct contact
- Virus persists giving life long immunity and antibody-detection
- Usually resolves spontaneously but can be treated by laser or cryo-freezing
Equine Sarcoids
- Most common untreatable tumor
- Locally aggressive tumor of integument
- Associated with Arabs and Thoroughbreds
- Thought to be associated with bovine papillomaviruses
- Virus entry through skin abrasions
- Flies may act as mechanical vectors