Parapoxviruses (PPVs) are zoonotic viruses that have been known for centuries to cause contagious pustular skin infections in sheep, goats, and cattle worldwide. These viruses also infect other animals, such as red deer, seals, camels, reindeer, and domestic cats. In the genus Parapoxvirus, 5 species are currently recognized: Orf virus (ORFV), bovine papular stomatitis virus (BPSV), pseudocowpox virus (PCPV), parapoxvirus of red deer in New Zealand (PVNZ), and squirrel parapoxvirus (SPPV), as well as the tentative species of the genus: auzdyk disease virus, chamois contagious ecthyma virus and sealpox virus. All recognized PPV species except PVNZ have been identified in humans. Manifestations of human PPV infections ("farmyard pox") are typically seen on the hands of persons who had contact with infected ruminants. The horse as an origin for zoonoses is not uncommon: as many as 58% of emerging zoonotic pathogens infect ungulates. Horses have a possible role as reservoir or vector of an emerging zoonotic poxvirus.
Orf or contagious ecthyma is a zoonotic viral infection caused by the orf virus. This infectious pustular dermatitis primarily affects sheep, goats and wild ruminants worldwide. Orf is characterized by proliferative skin lesions of the lips, muzzle, ears, eyelids, and found around the mouth and nostrils of lambs. The disease also results in genital, udder and foot lesions. Additional lesions are observed in the oral mucosa in severe forms of disease. The transmission within a herd is carried out through direct contact between animals during confrontation or suckling. The whole herd may be infected, while the mortality is usually less than 1%. Humans (farmers, butchers, sheep and goats shearers and veterinarians) can also be infected by direct contact with sick animals.2
Parapoxviruses cause dermal diseases in semi-domesticated reindeer. Several outbreaks of orf virus infection have been reported in Norway. Seven of the infected animals died, due to massive oral cauliflower-like lesions and secondary bacterial infections. This suggests that the orf virus crosses the host species barrier from sheep and goat to semi-domesticated reindeer. The outcome of parapoxvirus infections in reindeer seems to be dependent on many environmental factors in addition to the exposure to the virus. Certain types of stress is believed to play a key role, and such stress factors may be lack of food, as well as handling, corralling and transport of animals.6
Symptoms of bovine infection with bovine papular stomatitis virus (BPSV) can involve painful erosive papules or vesicles on the muzzle, lips and teats. The exception to this is that BPSV infection in young bovines is sometimes manifest with distinctive "horseshoe-shaped" papular lesions in the mouth, which can occur with or without inflammation of the gingiva.3
Pseudocowpox virus (PCPV) is very similar to the papular stomatitis virus. It infects cattle throughout the world and has zoonotic potential. The virus causes contagious ecthyma in sheep goats and dairy cattle. Lesions occur on the teats and ventral udder and are characterized by reddish, sensitive nodules, and circular raised areas that heal under thick crust. This feature helps to differentiate pseudocowpox virus from the cowpox virus. While cowpox virus is extremely rare in the United States, pseudocowpox is common in dairy cattle and is spread by milking equipment and milking hands. Leasons usually heal within 2-3 weeks, but may become chronic for unknown reasons.4
The Parapoxvirus of Red Deer in New Zealand (PVNZ) has only been reported in New Zealand. Genetically, PVNZ is closely related to BPSV and is responsible for a contagious pustular dermatitis in farmed red deer. Most PPVs are transmissible to humans, and these infections share clinical manifestations and exposure risks with other, potentially life-threatening zoonoses. The transmission of PPVs from deer to humans already has been reported; for these reasons, it cannot be ruled out that PVNZ could be transmitted to humans as a consequence of wildlife activities and manipulation of carcasses.5
Recently, a new zoonotic parapoxvirus from a skin lesion in a horse has been isolated. Clinical signs of the disease include severe dermatitis, fever, scrotal swelling, hard, nodular skin lesions and enlarged lymph nodes. Affected horses become apathetic and lose weight despite a good appetite.1