Viral skin infections - Pathology

Lesion development:
- Due to viral invasion of epithelium
- Vascular injury -> ischaemic necrosis
- Stimulation of host DNA -> hyperplastic nodules
Cutaneous lesions:
- Macule -> papule -> vesicle -> umbilicated pustule -> crust -> scar

Contagious ecthyma (Courtesy of Bristol BioMed Image Archive)

Also called contagious pustular dermatitis, orf, sore mouth
Caused by a parapox virus
Affects mainly young sheep, less commonly cattle, humans, dogs
Starts in abrasions around mouth commisures and spreads to lips, oral mucosa, eyelids and feet
May also transfer to teats of the mother of an affected lamb
Lesions typical of poxvirus but very brief vesicle stage
Most obvious is the proliferative pustular stage

Cutaneous lesions may develop with nondermatotropic viruses:
- Infectious bovine rhinotracheitis (bovine herpes virus - 1)
- Equine coital exanthema (equine herpes virus - 3)
- Feline herpes virus -1 (rarely)
Dermatotropic viruses:
- Bovine herpes virus - 2 = Bovine herpes mammillitis virus
  - May cause generalised disease - pseudolumpy skin
  - Localised disease - bovine herpes mammillitis
    - Mostly in lactating cows
    - Skin trauma is essential for virus invasion
    - Decreased milk production and secondary bacterial mastitis
    - Lesion occur on teats, udder, sometimes perineum, on muzzle of suckling calves
- Bovine herpes virus - 4 = Bovine herpes mammary pustular dermatitis
  - Similar to localised BHV-2 but milder disease