Papomaviridae

VIRUSES

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

Virus by Species

Canine Papillomavirus

• Occur in oropharynx of puppies aged 4-6 weeks
• Usually resolve spontaneously

Bovine Papillomaviruses

• 2 groups:

1. Fibropapillomas: viral DNA sequences, but no virus found
2. 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