CSU ext
Sore mouth, (contagious ecthyma, orf) is a parapoxvirus related to the viruses causing pseudocowpox (milkers nodule) and papular stomatitis of cattle.
Sore mouth is mainly a disease of sheep and goats and is a zoonotic disease.
How is it transmitted?  By direct contact with sores on sheep and goats and from indirect contact with infected scabs that contaminate the environment, stalls, halters etc.   People are rarely a source of infection for other people. Soremouth vaccine for animals is available, and should be used very carefully to avoid accidentally injecting the person doing the vaccinating as this will produce disease.

goat orf lesion
Sore mouth lesion on a goat

What are the signs in animals? Early in the infection sores appear as blisters and then become crusty scabs. The lesions are typically found on the lips, muzzle, and in the mouth but lambs and kids may get similar sores/scabs on the lower legs and the teats, especially when ewes or does are nursing infected lambs or kids. Young animals may have difficulty nursing/feeding and may require bottle or tube feeding. Nursing ewes may abandon their lambs due to painful teats.  Particular breeds (e.g. Boer goats) may be especially susceptible and have severe infections.  Animals typically recover completely from sore mouth infections within a month.
Lesion on the lips can resemble those of FMD, and therfore must be differenciated from FMD by a veterinarian.

sore mouth
Sore mouth lesion on a lamb
What are the symptoms in humans? People can develop painful sores on their hands. Lesions can persist for up to 2 months before healing.
orf lesion on a human
Orf lesion on a human
More information at Merck Vet Manual:
http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/71000.htm&word=Sore%2cmouth