Viral skin disease

Question 1

What properties of the skin help prevent infection by viruses?

Answer 1

• dense layer of keratin (physical barrier)
• low pH, presence of fatty acids (hostile environment)
• innate and adaptive immunity

Question 2

What are the disadvantages of skin if the viruses can overcome the barrier?

Answer 2

• rapidly dividing cells
• lots of blood vessels and lymphatics
• nerves

Question 3

How do viruses overcome the barrier?

Answer 3

• trauma/ abrasions (e.g. poxviruses)
• arthropods
  
  • as mechanical vectors (e.g. equine infectious anaemia)
  • or true arboviruses (e.g. Bluetongue virus)
• animal bites (rabies)
• iatrogenic (e.g. eartags)

Question 4

Describe the mechanism in which a virus (e.g. FMDV) shows clinical signs in the skin

Answer 4

• skin: invasion, multiplication
• regional lymph node, multiplication
• blood stream: primary viremia
• spleen and liver: multiplication, necrosis
• blood stream: secondary viremia
• skin: focal infection, multiplication

Question 5

How is rabies spread?

Answer 5

• spread through neurons, moves from peripheral NS to CNS

Question 6

What is this?

Answer 6

Question 7

What are the properties of papillomaviruses?

Answer 7

• small
• non enveloped
• not easily disinfected by organic detergents
• survives low pH and high temps
• ds DNA - genome is infectious

Question 8

How does the papillomavirus form a wart?

Answer 8

• needs actively dividing cells in basal squamous epithelial layer
• leads to virus induced hyperplasia
• virus shed with keratinocytes

Question 9

What is a wart?

Answer 9

• benign neoplasms that usually regress spontaneously

Question 10

How do some specific papillomaviruses progress to malignancy?

Answer 10

• virus genome is integrated into the host DNA
• thus the host cell is transformed (malignant transformation)
• site of integration is random
• viral oncogenes (E6 and E7) remain intact, and interact with cellular proteins such as tumour suppressor gene p53

Question 11

Give examples of papillomaviruses that progress to malignancy

Answer 11

• bovine papillomavirus 4
• bovine papillomavirus 7

Question 12

What species are warts most common in?

Answer 12

• cattle

Question 13

How are warts normally transmitted in cattle?

Answer 13

• by fomites e.g. headcollars

Question 14

How many types of wart are recognised in cattle?

Answer 14

• 10

Question 15

How do the warts form in cattle?

Answer 15

• hyperplasia and hyperkeratinisation 4-6 wks after exposure
• raised plaques
• proliferating epidermis
• pedunculated masses
• usually regress spontaneously 1-6 months
• in combo with Bracken fern, they can cause carcinoma in alimentary and urinary tracts (enzootic haematuria)

Question 16

What is the most common skin tumour in horses and at what age is it most common?

Answer 16

• sarcoids
• most common in horses under 4

Question 17

Where are sarcoids mostly found and why are they a problem?

Answer 17

• head, ventral abdomen, limbs
• locally aggressive but not malignant

Question 18

What virus are sarcoids associated with?

Answer 18

• bovine papillomavirus types 1/2
• BUT - unaffected horses can also have BPV DNA in the skin

Question 19

What papillomas are mostly found in young dogs? When do they regress?

Answer 19

• oral papillomas in young dogs
• regress - 8 weeks
• progressio to squamous cell carcinoma rarely

Question 20

What diagnostic techniques can be used?

Answer 20

• PCR - used to detect papillomavirus DNA and determine what virus is involved
• immunohistochemistry (presence of virus in lesion)
• histopathology

Question 21

What are some treatment options for warts?

Answer 21

• autogenous vaccination
• surgical debulking
• sarcoids:
  
  • surgery, radiation, topical drugs
  • immunotherapy (BCG, anti-BPV vaccines)

Question 22

What disease causes mortality in young captive psittacine birds?

Answer 22

• budgerigar fledging disease
• associated with French molt