Fowl Pox

Fowl pox is a viral infection that affects chickens and turkeys. It is slow spreading. There are 3 forms of fowl pox: Cutaneous (dry pox), Diphtheritic (wet pox) and Systemic. Fowl pox is world wide, but more prevalent in warm, high humidity areas and areas where there is a high population of mosquitoes as they are a vector for transmission. Outbreaks usually occur in winter and spring as mosquitoes tend to over winter in chicken houses.

Synonyms: chicken pox (not to be confused with chicken pox in humans; the human disease does not affect poultry and vice versa), sore head, avian diphtheria, bird pox.

Species affected: Most poultry—chickens, turkeys, pheasants, quail, ducks, psittacine (Birds of parrot family).

Cutaneous (dry pox)

This is the most common form of fowl pox and presents with proliferative lesions on the skin that develop into thick scabs. When lesions are small they can be difficult to distinguish from fighting/pecking injuries. Can turn into wet pox.

Diphtheritic (wet pox)

Lesions form in the upper GI tract and respiratory tracts. These lesions are caseous (cheese like) that can block the tracts affecting breathing and eating/drinking.

Systemic

Caused by virulent strains. Lesions form on internal organs.

Clinical signs: There are two forms of fowl pox. The dry form is characterized by raised, wart-like lesions on unfeathered areas (head, legs, vent, etc.). The lesions heal in about 2 weeks. If the scab is removed before healing is complete, the surface beneath is raw and bleeding. Unthriftiness and retarded growth are typical symptoms of fowl pox. In laying hens, infection results in a transient decline in egg production (see Table 1). In the wet form there are canker-like lesions in the mouth, pharynx, larynx, and trachea. The wet form may cause respiratory distress by obstructing the upper air passages. Chickens may be affected with either or both forms of fowl pox at one time.

Other symptoms include:

• Lesions on the face, head, wattles, feet and legs
• Nasal discharge
• Decreased egg production
• Weight loss
• Lethargy

Transmission: Fowl pox is transmitted by direct contact between infected and susceptible birds or by mosquitos. Virus-containing scabs also can be sloughed from affected birds and serve as a source of infection. The virus can enter the blood stream through the eye, skin wounds, or respiratory tract. Mosquitos become infected from feeding on birds with fowl pox in their blood stream. There is some evidence that the mosquito remains infective for life. Mosquitos are the primary reservoir and spreaders of fowl pox on poultry ranges. Several species of mosquito can transmit fowl pox. Often mosquitos winter-over in poultry houses so, outbreaks can occur during winter and early spring.

Treatment: No treatment is available, as it is viral and needs to run it’s course, which can take weeks. However, fowl pox is relatively slow-spreading. Thus, it is possible to vaccinate to stop an outbreak. The wing-web vaccination method is used for chickens and the thigh-stick method for turkeys older than 8 weeks. Iodine may be dabbed on dry pox lesions to help speed the healing process up and assist with possible secondary infection. Vaccination may help to lessen symptoms and prevent further spread, but only healthy birds should be vaccinated

Prevention: Fowl pox outbreaks in poultry confined to houses can be controlled by spraying to kill mosquitos. However, if fowl pox is endemic in the area, vaccination is recommended. Do not vaccinate unless the disease becomes a problem on a farm or in the area.

References: http://edis.ifas.ufl.edu/ps044

Merck Vet Manual – Fowlpox in Chickens and Turkeys

Small and Backyard Poultry – FOWL POX IN POULTRY