Mortality Threats to Birds - Avian pox (Poxvirus avium)


mosquito by USDA

A variety of birds worldwide play host to several strains of the avian pox virus, including gamebirds, poultry, songbirds, seabirds, and parrots. The virus was introduced in Hawaii in the 1800’s with the importation of domestic fowl. It was identified in an Apapane from Hawaii in 1902, and had been identified in domestic chickens in Honolulu the year before. However, it was not until the 1980’s that it was found in the Hawaiian Crow or Alala. Transmission is through direct contact with infected birds, ingestion of food and water contaminated by sick birds or carcases, or contact with contaminated surfaces such as birdfeeders. The virus enters through abraded skin. Insects, especially mosquitoes, act as mechanical vectors.


There are two forms of avian pox, cutaneous pox and diphtheric or “wet” pox. In the more common cutaneous form, wartlike growths occur around the eyes, beak, or unfeathered skin such as legs and feet. This leads to difficulty seeing, breathing, feeding or perching. Wet pox causes growths to form in the mouth, throat, trachea, and lungs, resulting in difficulty breathing or swallowing. Birds with either type appear weak and emaciated.

Birds Affected

Avian pox can be a significant factor in bird mortality, especially in endemic Hawaiian bird populations, as well as upland game birds, songbirds, and raptors. In Hawai'i, the Apapane, Omao, ‘Elepaio, Hawaiian Amakihi and the I’iwi are especially susceptible.


Disease control is site-specific. Birdfeeders and birdbaths need to be decontaminated with a solution of 10% bleach and water. In some situations, removing infected birds can be important to decreasing the amount of virus available to vectors and non-infected bird populations. Mosquito control of the larval stage is most effective.