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Fowl Pox

Other Names: Avian Diphtheria, Bird Pox, Contagious Epithelioma, Poxvirus Infection, Poxvirus Avium, Avian Pox

Fowl pox is a slow-spreading viral disease in chickens characterized by lesions on unfeathered skin and/or the mucous membranes of the mouth, larynx, and trachea. It is caused by avian poxvirus, which exists in several strains, including fowl poxvirus (affecting chickens and turkeys), pigeon poxvirus (affecting pigeons), and canary poxvirus (affecting various wild birds). Each strain is species-specific, meaning chickens cannot contract pigeon poxvirus, and vice versa.

Forms of Fowl Pox

Fowl pox occurs in two forms: the dry (cutaneous) form and the wet (diphtheritic) form.

Dry (cutaneous) form
This is the most common presentation. It causes small, wart-like lesions on unfeathered areas such as the comb, wattles, face, eyelids, legs, and feet. These lesions begin as small yellow bumps that gradually enlarge and darken into rough, brown scabs. Scabs typically persist for 2–4 weeks before falling off, leaving smooth scar tissue.

These scabs contain active virus and are highly infectious. When lesions develop near the eyes, chickens may initially show mild irritation that can progress to swelling, ulceration, and closure of the eyelids due to discharge or crusting. During this stage, birds are more susceptible to secondary infections, so keeping lesions clean is important.

Wet (diphtheritic) form
This more severe form is associated with higher mortality. It causes yellow, cheese-like plaques (canker lesions) to form in the mouth and throat. These lesions may begin as small white nodules that merge into larger patches. When present in the upper digestive or respiratory tract, they can interfere with eating, swallowing, and breathing, leading to reduced feed intake and respiratory distress.

Transmission

Fowl pox is commonly spread by biting insects, especially mosquitoes, as well as by introducing infected birds into the flock. After feeding on an infected bird, mosquitoes can carry and transmit the virus for up to 8 weeks, potentially infecting multiple chickens.

Within a flock, the virus spreads through:

Broken skin or mucous membranes: Often due to pecking or fighting.
Dried scabs: which can remain infectious in the environment for months or even years.

Diagnosis

Diagnosis is based on flock history, clinical signs, and physical examination. Laboratory confirmation can be performed through virus isolation, fluorescent antibody testing, electron microscopy, or testing of scab or lesion samples.

Treatment

Fowl pox is typically self-limiting, meaning it resolves on its own over time. Treatment focuses on supportive care, including maintaining good hygiene and monitoring for complications. Antibiotics may be required if secondary bacterial infections develop.

Clinical Signs

Scab or wart-like lesions on comb, face and wattles

Yellow canker lesions inside mouth

Sneezing

Coughing

Eye discharge

Difficulty swallowing

Diagnosis

History
Clinical signs
Physical exam
Diagnostic tests

Reported Cases

Case 1: Fowl pox in a Chickens Fowl Pox was diagnosed in three Houdan chickens submitted for diagnostic workup to the Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL) in Center, Texas. Upon examination, the birds had either one or both eyes severely swollen, due to a large accumulation of caseous exudate, and moderate numbers of dark brown, 3 mm diameter, raised nodules on the eyelids, cere, and skin adjacent to the beak. The palate had a yellowish diphtheritic plaque. The histopathological examination of eyelids and palate revealed characteristic fowl pox diagnostic lesions, including ballooning degeneration and hyperplasia of epithelial cells associated with eosinophilic intracytoplasmic inclusions. Additionally, Staphylococcus aureus was isolated from the conjunctiva of the affected eyes, which may have been a secondary infection to fowl pox. Ref

Case 2: Diphtheritic Fowl Pox in a Laying chickens Diphtheritic Fowl Pox, commonly called wet pox, was diagnosed in 11-week-old layer-type chickens experiencing increased mortality and respiratory signs. On gross exam, the birds had pinpoint hemorrhages of the conjunctiva and thick yellow diphtheritic plaques on the upper larynx and tracheal mucosa, which in the dead birds completely occluded the lumen. The diagnosis was confirmed by histopathology of trachea and larynx which had typical pox lesions. Interestingly, the birds had been vaccinated in the wing web for Pox and had only the diphtheritic form unaccompanied by skin lesions. Ref

Case 3: Pox and Otitis externa in a Backyard chickens Avian poxvirus caused severe otitis externa and media in a backyard flock hen with possible secondary bacterial infection. Ref

Case 4: Avian pox and flea infestation in a Rooster A mixed breed rooster from a backyard flock of 13 chickens, was received at the California Veterinary Diagnostic Laboratory System-Turlock Branch for postmortem examination. The bird presented with thickened, featherless, scab-encrusted skin around the head region. Numerous sticktight fleas were found attached to the encrusted skin. Microscopic evaluation of the skin revealed a lymphoplasmacytic reaction in the dermis with visible embedded flea mouthparts. Also noted histologically in this region were epidermal hyperplasia and ballooned epidermal cells containing intracytoplasmic inclusions indicative of fowl poxvirus. Ref

Case 5: Avian Pox with secondary infection in a Eagle A juvenile golden eagle was presented with proliferative epithelial lesions, consistent with avian poxvirus infection, around the eyes, on commissures of the beak, and on both feet. Despite treatment, the eagle declined clinically, and, 15 days after presentation, the eagle began seizuring and was euthanized because of a poor prognosis. On postmortem examination, avian poxvirus infection was confirmed in the nodular skin lesions, and Candida albicans was cultured from the skin, lungs, and brain. Breaks in the skin barrier from poxvirus infection likely led to secondary infection with C albicans. Systemic vascular dissemination of C albicans to the brain resulted in thrombosis, hemorrhage, local hypoxia, and the clinically observed seizures. The combination of the breach in the primary immune system, immunosuppression, and a prolonged course of antibiotics were contributory factors to the opportunistic fungal infection in the eagle. Ref

Case 6: Fowlpox with amyloidosis in a Chickens Cutaneous fowlpox occurring in vaccinated layer hens was investigated pathologically and microbiologically. Anorexia, decrease of egg production, increased mortality, yellow scabs on faces, and alopecia of feathered skins with yellow scabs were observed in affected hens. Histologically, proliferative and necrotic dermatitis with eosinophilic ring-shaped cytoplasmic inclusions (Bollinger bodies) and clumps of gram-positive cocci (Staphylococcus hyicus) were noted in the affected birds. Fowlpox lesions were primarily observed in the feathered skins. Proliferation of feather follicle epidermal cells, with cytoplasmic inclusions and degeneration of the feather, and bacterial clumps in the feather follicles were noted in the affected skins. Ultrastructurally, characteristic fowlpox viral particles were observed in the cytoplasmic inclusions of hyperplastic epidermal cells. Amyloid deposition was observed in the Disse space of the liver, splenic sinus, and lamina propria of the bronchiolar, bronchial, and tracheal areas. Amyloidosis could be one factor inducing the fowlpox infection in vaccinated chickens. Ref

Treatment

Name	Summary
Supportive care	Isolate the bird from the flock and place in a safe, comfortable, warm location (your own chicken "intensive care unit") with easy access to water and food. Limit stress.
When to call your veterinarian	If you suspect infection or if pox lesions are located near the eyes, inside the mouth, or affecting breathing.
Keep clean and dry	Apply silver nitrate, iodine, or 1-2% saline solution directly to the lesion. Once scabs have formed, they should not be physically removed. Using a hot or cold compress soaked in baby shampoo may be beneficial to press up against scabs to help them soften.
In cases involving the eyes	Early lesions should be flushed with dilute antiseptic or 1-2% saline solution.
Antibiotics	May be necessary to control secondary bacterial infections.
Vitamin A	Given as an adjunctive therapy to aid in healing.

Support

Prevention

Reduce mosquito populations by eliminating standing water and using traps or netting
Consider mosquito-repelling plants or approved insecticides near coops
Quarantine new birds before introducing them to the flock
Vaccination is also effective. Chickens are typically vaccinated using the wing-web method at 12–16 weeks of age, ideally 1–2 months before egg production or mosquito season. Annual vaccination may be recommended in high-risk areas.