Cowpox is a disease of the skin caused by a virus (Cowpox virus) that is related to the Vaccinia virus. The ailment manifests itself in the form of red blisters and is transmitted by touch from cows to humans. The virus that causes cowpox was used to perform the first successful vaccination against another disease. The disease vaccinated against was the deadly smallpox, which is caused by the related Variola virus. Therefore the word "vaccination" has the Latin root vaca meaning cow.

In 1798 the rural English physician Edward Jenner made a curious observation. His patients who had contracted and recovered from cowpox, a disease similar to but much milder than smallpox, seemed to be immune not only to further cases of cowpox, but also to smallpox. By scratching the fluid from cowpox lesions into the skin of healthy individuals, he was able to immunize those people against smallpox.

The Cowpox (Catpox) virus is found in Europe and mainly in the UK. Human cases are very rare and most often contracted from domestic cats. The virus is not commonly found in cows; the reservoir hosts for the virus are woodland rodents particularly voles. It is from these rodents that domestic cats contract the virus. Symptoms of infection with cowpox virus in humans are localized, pustular lesions generally found on the hands and limited to the site of introduction. The incubation period is 9-10 days. The virus is prevalent in late summer and autumn.

Note

This site: http://www.stanford.edu/group/virus/pox/history.html states that the vaccinia virus is not the same as cowpox.