Orf virus is a member of the Poxviridae family. It produces disease mainly among sheep, goats, and musk oxen, but can occasionally be transmitted to humans. Farmers and veterinarians are among the most likely to be exposed to the virus.
The orf lesion is approximately 1.5 cm in diameter, and is usually a solitary lesion located on the dorsal aspect of the finger. Regional lymphadenopathy, lymphangitis, and fever are common symptoms.
The disease passes through several distinct stages. 1) The lesion begins as a red, solid, elevated papule. 2) Next, it enlarges into a nodule with a red center, white middle ring, and red periphery (the target stage). 3) In the acute stage, a red weeping surface is present. 4) In the regenerative stage, a thin, dry crust develops, through which black dots may be seen covering the surface of the nodule. 5) In the next stage, small papillomas, or tiny growths, cover the surface. 6) Finally, during the regressive phase, a thick crust develops over the surface of the lesion, papillomas decrease in size, and the lesion flattens out.
Differential Diagnosis: The orf lesion can be distinguished from cutaneous anthrax in the following manner.
*Lesion is found primarily on the dorsal fingers of farmers and veterinarians
*Patient has had contact with sheep, goats, and musk oxen
*Lesion is associated with crusts and scabbing
* Ulcer and eschar are surrounded by characteristic non-pitting edema
* Lesion is not limited to fingers
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