Avian Pox

This fact sheet was updated on 2/7/2021.

Other names: Bird Pox, Fowl Pox, Avian Diphtheria

Cause

Avian pox, caused by a poxvirus, is one of the oldest known infectious disease of birds. There are many different strains of the avian pox virus but most are species specific. However, some strains have the ability to infect birds across different families.

Significance

While avian pox infections in wild birds are often mild and self-limiting, some outbreaks cause high mortality rates. Birds native to isolated islands are particularly susceptible to this disease. In Hawaii, avian pox has negatively impacted many species of native birds. Avian pox can lead to significant losses when many captive birds are housed in close quarters. The virus can also spread between wild and captive birds (see Transmission). 

Species Affected

Most bird species are believed to be susceptible to avian pox. About 230 species of wild and domestic birds have been reported with this disease; turkeys, finches, and doves are the most commonly affected wild bird species in New England. Upland game birds (such as mourning doves and wild turkeys), songbirds, and raptors can experience varying degrees of mortality due to avian pox. Wild waterfowl in North America have recently experienced an apparent increase in infection rate, though infections in these birds are still relatively uncommon. Domestic birds can also become infected with this virus but wild birds are not thought to be a major source of infection for domestic birds. Avian poxviruses are not known to infect humans. 

Distribution

Avian pox is distributed worldwide except Antarctica, the Arctic, and some other remote regions. Infection rates appear to be greater in areas with temperate and warmer climates. The virus has been introduced to several remote islands such as Hawaii, the Galapagos, and the Canary Islands where it spreads rapidly among the native bird populations. Poxvirus outbreaks are common in aviaries, rehabilitation centers, and whenever captive birds are housed closely together. 

Transmission

Biting insects such as mosquitoes, mites, fleas, midges, and flies are most frequently responsible for transmitting avian pox. These insects pick up virus particles when they take a blood meal from an infected bird and then transmit the virus when they do the same with another susceptible bird. Transmission rates are highest when biting insects are abundant. The virus can also be acquired via direct contact with infected birds or contact with contaminated objects such as bird feeders. Avian poxvirus is highly resistant to drying and can remain infectious for months to years in dried scabs and on contaminated surfaces. The virus particles can become aerosolized and infect susceptible birds via inhalation, though this is rare. Birds can become infected by ingesting contaminated food or water. The virus can also enter the body through skin abrasions. Transmission rates are also influenced by bird population density, and higher infection rates occur when bird densities are greatest. 

Clinical Signs

Avian pox develops slowly in affected birds. The most common clinical sign of avian pox is the formation of wart-like growths on the skin, particularly on unfeathered parts of the body such as the legs, feet, eyelids, base of the beak, and the comb and wattles. This is the cutaneous or “dry” form of avian pox. Birds with mild infections may only have a few growths that minimally affect their health status. These lesions can persist from 1 to 4 weeks but in most cases, the bird will survive and the nodules will heal potentially with some scarring. At times, nodules on the eyes can interfere with the bird’s ability to see food or predators and can lead to death. Mortality can also result from secondary bacterial infections that are common with this disease.

In more severe cases, birds may develop yellow-white, cheese-like lesions in their mouths and upper respiratory tract (this is known as the diphtheritic or “wet” form of the disease) which can lead to decreased food intake, difficulty breathing, and death. 

Diagnosis

A presumptive diagnosis can be made based on clinical signs but laboratory tests (microscopic examination, virus isolation, serology, or PCR) must be conducted to confirm diagnosis.

Treatment

There is no known treatment for avian pox in wild birds. In captive birds, a variety of treatments have been used along with supportive cate to treat the pox lesions and prevent secondary infections. These methods will not eliminate the virus, and the disease will run its course with or without treatment.

Management

The main goal of avian pox control efforts is to prevent further disease transmission. Mosquito control and elimination of breeding sites can be an important aspect of poxvirus transmission prevention. Severely infected birds should also be removed. Avian pox is often transmitted when birds congregate at bird feeders. When outbreaks occur, bird feeders, baths, and cages should be decontaminated with a 10% bleach and water solution (9 parts water:1 part bleach). The domestic poultry industry vaccinates against avian pox, but the safety and effectiveness of such vaccines in wild birds is currently unknown and likely not feasible on any large scale. 

Suggested Reading

Images

Wild turkey with avian poxWild turkey with avian pox; photo courtesy of PSU Animal Diagnostic Lab