Pox diseases are acute viral diseases that affect many animals, including humans and birds, but not dogs. Some poxviruses also cause zoonoses. Typically, lesions of the skin and mucosae are widespread and progress from macules to papules, vesicles, and pustules before encrusting and healing. Most lesions contain multiple intracytoplasmic inclusions, which represent sites of virus replication in infected cells. In some poxvirus infections, vesiculation is not clinically evident, but microvesicles can be seen on histologic examination and, in some, proliferative lesions are characteristic.

Infection is acquired either by inhalation or through the skin (eg, sheeppox). In certain instances (eg, fowlpox, swinepox), the virus is transmitted mechanically by biting arthropods. Infection may be followed by generalized lesions (eg, sheeppox) or remain localized (eg, pseudocowpox). Strains of poxvirus with reduced virulence are used to immunize against some infections, the classic example being the global eradication of smallpox in humans by immunization with strains of live vaccinia virus.

Poxviruses can be classified according to their physicochemical and biologic properties. Immunologically, the viruses of smallpox, cowpox, monkeypox, etc, are closely related to vaccinia virus and are classified within the genus Orthopox. The avian poxviruses, the myxoma viruses, and some of the other poxviruses (eg, swinepox) are species-specific. The viruses of orf, pseudocowpox, and bovine papular stomatitis are parapoxviruses.

In Europe, localized skin infections, and in some cases fatal generalized disease, have been reported in cheetahs, lions, and domestic cats infected with cowpox virus (see Pox Diseases: Cowpox).

Last full review/revision July 2011 by Paul Gibbs, BVSc, PhD, FRCVS