Papular proliferative pathology
- Parapox virus
- Very similar disease to orf but seen in cattle and generally milder condition.
- Must be differentiated from Foot and Mouth Disease and Mucosal Disease.
- Sporadic, in cattle, less than 1 year old.
- Develop papules on the muzzle, external nares and in the oral cavity; the oesophagus and forestomachs may also be affected.
- Usually heals spontaneously.
Pathogenesis
- The early lesions are round areas of intense congestion up to 1.5 cm in diameter.
- The centre becomes necrotic and slightly depressed.
- Slow peripheral extension of this lesion gives a classical ring zone formation with concentric rings of
- yellow (necrosis),
- grey (epithelial hyperplasia)
- red (congestion).
Histology
- There are focal areas of hydropic degeneration in the stratum spinosum
- Large eosinophilic intracytoplasmic inclusion
- Epidermis is markedly thickened.
- The superficial layers of the epithelium become necrotic and slough.
- Vesicle formation is not a feature of this disease.