ORF (FARMYARD POX)
The pathology of orf is essentially that which is seen in a milker's nodule. Swollen keratinocytes may become bags of clear cytoplasm (ballooning degeneration), and the ballooned cells rupture is such a fashion as to create a network of cytoplasmic remnants (reticular degeneration). Epidermal necrosis follows these changes. These changes are seen in other viral infections, notably herpetic infections. The dermal inflammatory infiltrates in farmyard pox  sometimes contain eosinophilic leukocytes, which are not characteristic of herpetic infections. Cytoplasmic and, less commonly, intranuclear inclusions are seen in some cases. Pseudoepitheliomatous hyerplasia of slender rete ridges is seen in some cases but not in the one presented here.

This is a biopsy of a large, rapidly growing, weeping, solitary lesion on the dorsum of the hand of a 35 year old female. She gave a history of contact with sheep, and this lesion spontaneously resolved.
 
Scan power view showing massive infiltration of the full thickness of the dermis by inflammatory cells plus epidermal alterations. Epidermal necrosis is seen in the left side of the picture.
Low power view of the epidermis. All of the keratinocytes are enlarged.
A high power view of the epidermis. Tremendous intracytoplasmic edema results in ballooning degeneration.
Another high power view of the epidermis. Early reticular degeneration is present.
A very high power view of the epidermis. An intracytoplasmic inclusion body (IB) is present.
Another very high power view of the epidermis. Other inclusion bodies are seen.
A high power view of the dermis. Lymphocytes, histiocytes, and eosinophilic leukocytes form the inflammatory infiltrates.

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