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, smallpox, which is caused by the related Variola virus. Therefore the word "vaccination" has the Latin root vaca meaning cow.
