Orf is a farmyard pox, a type of zoonosis. A pale halo forms around a red centre. It may persist for several weeks before crusting and then either resolves or leaves a granuloma. It can occur in humans who handle infected animals or contaminated objects. One-third of cases may develop erythema multiforme.
One Health perspective
thumb|right|300px|A sheep with signs of orf virus (contagious [[ecthyma). Monitoring livestock is a key part of the One Health approach to preventing zoonotic spread.]]
Orf is a classic One Health challenge involving interactions among the environment, livestock, and humans. The virus is highly resistant to physical factors; it can survive in dry soil or on farm equipment for several months to years, even after infected animals have been removed. This environmental persistence creates a reservoir for future outbreaks. Because the virus is zoonotic, protecting animal health through vaccination and biosecurity directly protects the health of the farming community and the local economy.
Humans
Orf is a zoonotic disease, meaning humans can contract this disorder through direct contact with infected sheep and goats or with fomites carrying the orf virus. It causes a purulent-appearing papule locally and generally no systemic symptoms. Infected locations can include the finger, hand, arm, face and even the penis (caused by infection either from contact with the hand during urination or from bestiality). Consequently, it is important to observe good personal hygiene and to wear gloves when treating infected animals.
Other animals
Orf is primarily a disease of sheep and goats although it has been reported as a natural disease in humans, steenbok and alpacas, chamois and tahrs, reindeer, musk oxen, dogs, cats, mountain goats, bighorn sheep, dall sheep, and red squirrels. Occasionally the infection can be extensive and persistent if the animal does not produce an immune response. The vaccine can cause minor cases of orf when used in humans.
In sheep and goats, the lesions mostly appear on or near the hairline and elsewhere on the lips and muzzle. In some cases the lesions appear on and in the nostrils, around the eyes, on the thigh, coronet, vulva, udder, and axilla. In rare cases, mostly involving young lambs, lesions are found on the tongue, gums, roof of the mouth and the esophagus. It has also been reported a number of times to cause lesions in the rumen. In one case it was shown that a severe form of orf virus caused an outbreak involving the gastrointestinal tract, lungs, heart, as well as the buccal cavity, cheeks, tongue and lips. Another severe case was reported pharyngitis, genital lesions and infection of the hooves which led to lameness and, in some cases, sloughing of the hoof.