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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 of chickens characterized by lesions on the unfeathered skin areas and/or mucous membranes of the oral cavity, larynx, or trachea. The disease is caused by the avian poxvirus which is classified as at least three different strains or types, including fowl poxvirus (FPV) that affects chickens and turkeys, pigeon poxvirus (PPV) that occurs in pigeons, and canary poxvirus (CPV) that affects different species of wild birds. Each virus strain can only cause disease within certain species of birds. For example, chickens are not affected by infection with pigeon pox virus, and vice versa.

Forms of Fowl Pox


There are two different forms of fowl pox that can occur in chickens--classified as a dry (cutaneous) form and wet (diphtheritic) form.
Cutaneous or "dry" pox form
The cutaneous or "dry" pox form is the most common. Typical pox lesions are small, wart-like growths on the skin of unfeathered areas (face, comb, wattles, eyelids, legs, and feet). These initially appear as small, yellow eruptions which gradually increase in size. Pox lesions will also change color as they grow larger, and turn into dark brown, roughened, dry scabs. The scabs will usually last about 2 to 4 weeks, afterwhich they will loosen and drop off on their own, leaving smooth scar tissue underneath. These dry scabs contain the poxvirus and are highly infectious to other flock members.

In cases where pox lesions develop near the chicken's eyes, clinical signs may initially present as mild redness and irritation and quickly progress to swelling of the eyelid and the development of ulcerative lesions along the edges of the eyelid. The eyelids often become sealed shut with caseous discharge or with dry crusting scabs which fall off within two weeks. While lesions start to develop, affected chickens are at an increased risk of secondary infection. To minimize risk of infection, efforts should be made to help keep pox lesions clean.

Diphtheritic (wet pox) form
The diphtheritic form of fowl pox is associated with higher mortality in birds. It causes plaques (also referred to as yellow canker lesions) to develop within the oropharynx (inner mouth and throat) of birds. These may start out as tiny white nodules which merge together to form raised-yellow white cheesy patches. If lesions are located in the upper digestive and respiratory tract, it may cause chickens to reduce their feed intake and have difficulty swallowing. Other respiratory signs may also be apparent, depending on the severity which can range from mild to severe.
fowl pox disease timeline

How Fowl Pox is Transmitted


Fowl pox is transmitted to flocks through biting arthropods (primarily mosquitoes) and introduction of a new bird into the flock who is latently infected with the virus. Once a mosquito feeds on an infected bird, it is able to keep the virus in it's salivary glands for up to 8 weeks. When mosquitoes bite another chicken, they are capable of transmitting the poxvirus to them. In fact, one mosquito can infect several chickens after feeding on a single bird infected with the virus.

Once one flock member is infected, the chicken is capable of transmitting the virus to other flock members by:
  • Through scratches or broken skin and mucous membranes: It is often associated with flock members pecking, fighting, or scratching at one another.
  • Dried pox scabs: The dried scabs that fall off of the chickens during the course of the disease can also serve as a source of infection in chicken flocks. The virus can survive in the dried scabs for months or even years.

Fowl Pox Treatment in Chickens


Generally, fowl pox is self-limiting and treatment is primarily supportive care. Antibiotics may be needed if secondary infection develops.

Clinical Signs

Eye discharge
Scab or wart-like lesions on comb, face and wattles
Yellow canker lesions in mouth
Sneezing
Coughing

Diagnosis

  • History
  • Clinical signs
  • Physical exam
  • Poxvirus - Virus isolation, fluorescent antibody, electron microscopy, agar gel immunodiffusion of scab with underlying epithelium, upper respiratory tract, or nodular lesions

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

NameSummary
Supportive careIsolate 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. Call your veterinarian if you suspect infection or if pox lesions are located near the eyes, inside the mouth, or affecting breathing.
For dry poxIt is important to keep pox scabs clean and dry. Apply silver nitrate, iodine, or 1-2% saline solution directly to the lesion to help keep clean.

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 eyesEarly lesions should be flushed with dilute antiseptic or 1-2% saline solution.
AntibioticsMay be necessary to control secondary bacterial infections.
Vitamin AGiven as an adjunctive therapy to aid in healing, 2000 U/kg PO, IMSpeer, 2016

Support

Prevention

  • Minimize risk of mosquitoes by eliminating stagnant water sources, incorporating mosquito traps near chicken coops, utilize mosquito proof netting, and/or apply insecticidal spray (specifically made to deter mosquitoes).
  • Keep mosquito repelling plants near chicken coops.
  • Vaccination - Using wing-web stick method, vaccinate chicks at at 12-16 weeks of age, 1-2 months before egg production with fowlbox attenuated live vaccine. Vaccinate annually 1-2 months before mosquito season. Chicks can be vaccinated at hatching with attenuated Avian poxvirus of tissue culture origin but this will not produce lasting immunity. If transmission is unlikely in the interim, initial vaccination could be postponed until after 4 weeks of age when a better and lasting immune response can be expected.

Prognosis

The diphtheritic form of fowlpox can cause up to 60% mortality in unvaccinated chickens

Scientific References

Good Overviews

Risk Factors

  • Exposure to mosquitoes, biting midges, and mites.
  • Introducing a new bird into the flock without following proper quarantine procedures.
  • Standing water sources

Case Stories

Seasonality

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