Orf

"Orf" is name given to a skin condition in humans caused by the same parapoxvirus that causes "contagious ecthyma" or "contagious pustular dermatitis" in sheep and goats.

Orf in humans:

• Chronic (weeks to months), poorly healing exudative papules, develop most commonly on the hands and arms.
  • The virus is acquired by direct contact with exudates from sheep or goats with clinical lesions. In fact, in a recent study, 23% of people in the U.K. employed or living on a sheep farm had had orf at some point in their lifetimes.

Contagious ecthyma in sheep and goats:

• exudative, crusty lesions on the lips and surrounding skin, legs, vulva and/or udder
  • The lesions are very painful and debilitating. When present around the mouth, affected animals may not be able to eat.

Milkers' nodules

Milkers' nodules are caused by infection of people with either cowpox virus (an orthopoxvirus) or pseudocowpox virus (a parapoxvirus). These are relatively benign lesions that occur most commonly on the hands or arms of people. The viruses are most commonly contracted by contact with cattle with cowpox or pseudocowpox teat lesions. (However: note that, despite the name, the primary reservoir for cowpox virus is actually rodents.)

• Following an incubation period of several days, the lesions begin as an erythematous papule, possibly with associated vesicles. These progress over a period of weeks to form reddish-blue to brown firm nodules.
• In some cases there may also be suppuration and scabbing.
• The lesions eventually heal without a scar, but this may take as long as 6 weeks, and the lesions may be quite painful.
  • click here to see photos of a pseudocowpox virus teat lesion on a cow

References:

Moriello, K. A. and J. Cooley. 2001. Difficult dermatologic diagnosis. J.A.V.M.A. 218:19-20. (Contagious pustular dermatitis)

Paiba, G.A. et al. 1999. Orf (contagious pustular dermatitis) in farmworkers: prevalence and risk factors in three areas of England. Vet. Rec. 145:7-11.

Pelkonen, P.M. et al. Cowpox with severe generalized eruption, Finland. Emerg. Infect. Dis. 9:1458-1461.