Papillomas, or warts as they are commonly called, are caused when a papillomavirus infects the outer most cells of the skin. The clinical problems associated with warts are primarily associated with skin. Once the papillomavirus takes over a cell, it causes the cell to undergo cancerous changes resulting in a thickening of the skin and development of a mass.

While many papillomaviruses have a preference for the skin, in humans some papillomaviruses have been known to infect and cause cancerous changes in the mouth, gastrointestinal tract and reproductive tract. The papillomavirus associated with the formation of warts on the skin of birds is considered to be a type of benign tumor.

Papillomas of the skin caused by a papillomavirus should be differentiated from papillomatosis, which is a wart-like lesion that can occur on the surface of the cloaca or along the gastrointestinal tract in psittacine birds. Recent research suggests that papillomatosis is probably caused by a virus.

Papillomaviruses have been identified in a wide variety of animals, humans, many other mammals and birds. The most commonly affected species of birds include finches, waterfowl, cranes, herons and flamingos. Papillomaviruses tend to be highly host-specific and the papillomaviruses that infect companion birds are not known to infect humans or other unrelated species of birds. It is probable that other variants of this virus will be identified in psittacine birds.

Warts in birds are similar in appearance to those in people. The skin lesions associated with papillomavirus appear similar to those caused by some avian poxvirus. Although a virus has yet to be demonstrated, papilloma-like lesions have been diagnosed microscopically in association with proliferative growths originating from skin overlying the toes, uropygial gland, mandible, neck, wing, eyelids and beak commissure from various psittacine species. A herpesvirus has been documented in wart-like growths on the feet of cockatoos and macaws. It is not known if this herpesvirus causes these skin changes or merely replicates in the damaged skin cells.

The factors associated with papillomavirus transmission in birds are unconfirmed. It is probable that birds are exposed through direct contact with an infected bird or through contact with a contaminated surface (perch, enclosure, table, food bowls, etc). Papillomaviruses are considered to be relatively stable when outside of the host. Because the incubation period for papilloma development in birds is unknown, it is usually difficult to determine when, where, and how a bird may have been exposed to a papillomavirus. Cool, moist conditions and freezing will preserve the infectivity of most viruses.