All Cooped Up: Fowlpox
Reading Time: 5 minutes
What is it? A viral infection affecting mainly chickens and turkeys but can affect other avian species.
Causative Agent: Viruses in the family Poxviridae.
Incubation period: 4-10 days.
Disease duration: 2-4 weeks.
Mortality: Low in the cutaneous form (dry pox), higher in the diphtheritic form (wet pox). If not controlled and treated appropriately the mortality rate rises.
Signs: Wart-like lesions on combs, wattles, eyelids, or feet, eyelid swelling, weight loss, decreased intake of food and water, and a reduction in egg production. Birds with the diphtheritic form will have lesions in the throat and respiratory tract.
Diagnosis: Through a veterinarian or laboratory.
Treatment: There is no treatment; fowlpox usually resolves on its own or results in death. Vaccinations can prevent the spread of and the initial outbreak of the disease.
Fowlpox is an old viral poultry disease that frequently affects backyard flocks. It is found worldwide and was first described as early as the 17th century. It is most commonly seen in chickens and turkeys, but almost every bird species can become infected including wild birds and indoor birds like canaries.
This disease is caused by avian pox viruses from the genetic family Poxviridae. There are several different strains of the virus that have been identified, which are named after the primary bird infected. There are two forms of this disease. The cutaneous form is the less deadly type and is colloquially referred to as “dry pox.” The diphtheritic form is a more serious infection affecting the upper respiratory and GI tract, also known as “wet pox.”
The cutaneous form is fairly recognizable with signature, wart-like lesions covering any non-feathered parts of a bird. Most commonly lesions will appear first on the comb, wattles, and around the eyes of chickens, and on the skin of the head on turkeys. Fresh lesions appear as yellow spots or blisters, which in turn scab over to form darker, wart-like growths. The lesions will change color and grow larger as the disease progresses, and additional lesions may begin to appear on the legs and feet, or any area on the body without feather covering.
Some cases of fowlpox have noted scabs forming on the eyelids of infected birds. In these cases, the eye can swell shut, causing partial or complete blindness for the duration of the disease. Should this happen, the bird will need to be isolated and given water and food separately to prevent starvation or dehydration. In the instance of a breakout, monitor birds daily for visual acuity.
Other clinical findings in infected birds are more generalized and related to average signs and symptoms of sickness. Egg production will drop in production birds. The bird will lose weight and have a reduced appetite for food and water. Young birds will exhibit poor growth. Birds of all ages may have a depressed appearance and become less active than normal.
The dry form scabs usually stay on the bird for two to four weeks before softening and dropping off. During this time, infected birds are highly contagious toward non-infected birds, and efforts should be made to control the spread of the disease. Any area the birds are staying in will need to be meticulously cleaned because the scab casings will have the fowlpox virus in them. Once the disease resolves itself, any surviving birds who contracted it will be naturally inoculated from future outbreaks of the same strain although another strain may still infect the birds. In rare cases, the dry form will continue to worsen without treatment and will not resolve on its own.
The diphtheritic form is far more deadly and is also known as “fowl diphtheria.” Where the cutaneous form exclusively affects the exterior of the bird, the diphtheritic form causes lesions internally on the mucous membranes of the mouth, throat, or trachea. The lesions start as small white nodules and quickly turn into large patches of caseous, yellow growths.
Growths in the bird’s mouth or throat interfere with food and water intake and may hasten dehydration and malnutrition. If the trachea is affected, the respiratory status of the bird may become compromised. Birds having this form will also appear depressed, weak, show a reduction in egg production, and exhibit loss of appetite. Generally, birds with wet form will not survive the infection without intensive treatment.
Flocks and individual birds alike can become infected with both forms of fowlpox at the same time. Having both forms at once is a larger attack on the bird’s immune system and subsequently, the death rate rises. Although a single bird may clear the disease in two to four weeks, it may take months for an entire flock to work through the infection because members will become infected at different times. Once a bird is infected once, they will not become infected again even if it stays with the flock.
Fowlpox is transmitted primarily through mosquitos. When a mosquito bites an infected bird, it can carry the disease for up to eight weeks. In that time, it can infect any bird it bites that has not been inoculated. It only takes one bird to become infected for the disease to spread through the entire flock.
An infected bird can give the disease to its flock members through open skin or mucous membranes in situations like picking or fighting. Owners can mechanically spread the disease as well, so take care when handling infected birds. The virus is shed from the infected bird when it starts dropping scabs as it heals. Birds of any age can contract the disease at any time of year. During mosquito season, follow basic control measures such as dumping standing water, adding plants that repel mosquitos to the landscaping, and reporting any dead wild birds to your local mosquito control group.
The cutaneous form can be identified at home with the help of an experienced poultry owner. Sometimes fighting wounds can be mistaken for fowlpox. The diphtheritic form will need a veterinarian’s diagnosis because the lesions are identical to a number of other serious poultry diseases. A sample will need to be taken and identified in a lab. This is incredibly important, because if it is a different disease then a different course of action will be needed.
Once a flock has contracted fowlpox, supportive therapy is most helpful. There aren’t any medications that help with the disease but monitoring the birds to make sure they’re eating and drinking enough, protecting from drafts, and basic maintenance will help them fight the infection themselves. If less than 20% of the flock is showing signs of the disease, vaccinate the healthy birds to help control transmission.
Great news! Unlike many diseases, fowlpox vaccines are actually available to backyard flock owners. There are several different vaccinations available over the counter. Follow the directions on the package for the route of administration depending on the age of the bird. Generally, chickens are vaccinated via the wing-stick method and turkeys get the vaccine brushed onto the surface skin of their thigh.
In high-risk areas with a large mosquito population, chickens and turkeys should be vaccinated in the first few weeks of life with an attenuated vaccine, and again in 12-16 weeks as a preventative measure. Due to possibly mishandling the vaccine and possibly giving the flock the disease, vaccines should only be administered by a veterinarian.
Check birds a week after vaccination for swelling and scab formation at the site. These signs are good and indicate successful inoculation. Do not vaccinate birds who already show signs of the disease. Once your flock has had an outbreak of fowlpox, they are carriers for life.
All Cooped Up is a collaboration between medical professional Lacey Hughett and poultry specialist at the University of Pennsylvania, Dr. Sherrill Davison. Every All Cooped Up publication has been vetted by Dr. Davison.
Originally published in the June/July 2020 issue of Backyard Poultry and regularly vetted for accuracy.