Rarely, cutaneous dissemination and even death may occur. Cowpox is caused by the cowpox or catpox virus, a member of the orthopoxvirus family, which also includes smallpox and vaccinia. The virus is thought to be acquired by direct contact with an infected animal, most often a cat in the case of humans, with lesions occurring where the virus gains access through broken skin. Infection generally remains localized at the initial site of inoculation, though lymphatic spread in a sporotrichoid pattern and generalized skin infection have been reported. The majority of cases have been reported in Great Britain, with a small number from Germany, Belgium, France, Sweden and Norway.
Most cases occur in the late summer and fall.
The host immune response is usually sufficient to control the viral infection and the only sequelae are scars at the site of the pox lesions. The only reported death associated with cowpox was in an atopic patient who was receiving systemic steroids for asthma at the time of his infection. After developing widespread cutaneous lesions, he died from pulmonary embolism. Autopsy failed to demonstrate viropathic effect in any internal organs, so it is unclear what role cowpox may have played in his death. No racial predilection has been reported.