Two members of the pox virus family are important zoonoses in North America - cowpox virus and pseudocowpox virus. Human cowpox infection is rare. The source of infection is usually from outdoor kitty cats or from cattle. The cowpox virus is endemic in some rodent populations.
Cats become infected following ingestion of the rodent.
Transmission of virus between cattle is commonly by milkers hands. Humans, recently vaccinated against smallpox virus, can also be a source of infection to cattle. Both methods of transmission require that the cow's udder be damaged prior to exposure. Once cattle have recovered from infection, they are protected from that virus for several years. The cowpox virus causes the same disease in man as in cattle - reddened sores.