Avian Poxvirus (APV), a large DNA virus, belongs to the Poxviridae family and  classified in the genus Avipoxvirus. This virus is distributed worldwide with the potential to infect and cause disease in poultry, pet, and wild birds. There are 10 recognized avipoxvirus species, with the exact number ever changing with the continued identification of new isolates from a variety of avian species.  To date, more than 230 species in 23 orders of birds are affected by avipoxvirus. Migration, habitat change, and species introductions play a vital role in the spread of pox, with potentially damaging effects in raptors, especially in small and endangered populations, particularly island species. 

There are three distinct forms of APV infections. The cutaneous form affects the unfeathered portions of the bird’s skin. Dry crusted proliferative wart like lesions may occur on the legs, feet, around the beak, nares, and eyes. The diphtheritic form results in fibrino-necrotic and proliferative lesions involving the digestive and upper-respiratory tract. This form is also known as wet pox and in general has a higher mortality rate than the cutaneous form. The systemic form often results in death and is characterized by lethargy, depression, cyanosis, anorexia, and wart like lesions of the skin. Raptors are usually affected by the cutaneous form and in most situations APV is self-limiting, requiring 2-4 weeks to heal. Scars can be visible following recovery and healing of the skin lesions.  Raptor mortality is often low, however pox lesions affecting the feet or beak and compromising the raptor’s ability to hunt, or complications of secondary bacterial and fungal infections can compromise the health of the raptor and result in death (fig 1).  Field studies comparing active infections (visual lesions) with an infection history (IgY antibodies) suggests that exposure to avipoxvirus is not a rare occurrence and that many raptors can mount an effective immune response preventing visible pathological changes. Raptors with APV infections most commonly present in the late summer and fall depending on the geographical location. Adult raptors may have a higher resistant to infections versus the passage or first year raptor.

APV is very resistant to environmental degradation and can survive for years in a dry environment. Transmission commonly occurs through a break in the skin, often the result of biting insects such as mosquitos and arthropods. Direct contact with an infected bird, or contaminated objects, ingestion of contaminated food or water and aerosols from infected birds is also a means of transmission.   Concerns for this highly transmissible virus and its immunosuppressive effects on a threatened or endangered species becomes worrisome as in the case of infected Turkey Vultures (Cathartes aura) feeding at the same sights as the California Condor (Gymnogyps californianus) and the Andean Condor (Vultur gryphus), where interspecies transmission may occur.  APV may be confirmed by visual lesions present but definitive diagnosis is identification through cytology and histology of the large intracytoplasmic, lipophilic inclusion bodies (Bollinger bodies) found in the epithelial cells of the integument, respiratory tract, and oral cavity (fig. 2).