pox disease, any of a complex of viral diseases in humans and other animals, marked chiefly by eruptions of the skin and mucous membranes. Pox diseases occur worldwide and are caused by viruses in multiple different genera; examples include Avipoxvirus, Leporipoxvirus, Orthopoxvirus, and Parapoxvirus. Examples of pox diseases include sheep pox, horse pox, fowl pox, cowpox, goat pox, and swine pox. Transmission occurs in different ways, depending on the virus. Some pox viruses are spread by direct contact, whereas others may be transmitted via inhalation of infectious particles or by biting insects. Cowpox (vaccinia) and pseudocowpox (paravaccinia), for example, which are localized on the udder and teats of cows, are transmissible to humans by skin contact. Some pox diseases also are more severe than others. Swine pox, for example, is prevalent but rarely fatal. Sheep pox is the most severe pox disease of domestic animals; both sheep pox and goat pox are often fatal.