Fowl pox is a viral disease characterized by skin lesions (changes). Although there is another form of the disease, in which changes appear in the mouth and upper respiratory tract, this form of the disease is also usually associated with skin changes in some birds. The disease was once widely prevalent, but with the arrival of vaccination its incidence is greatly reduced. However, still in some areas it continues to be of considerable economic importance.
Cause
A virus - called avipoxvirus. Fowl pox virus infects birds of both sexes, of all ages and breeds.
Spread
I. Spread of the virus from one bird to another by direct contact is the main method of spread. Most
of the spread is the result of birds picking, fighting, or scratching one another. Some break in the skin is required for the virus to enter the cells, grow, and cause disease.
2. Infection also occurs by mechanical spread of virus to the injured skin. Individuals handling birds at the time of vaccination may carry the virus on their hands and clothes, and may unknowingly deposit the virus in the eyes of susceptible birds.
3. Mosquitoes are known to transmit the disease and produce eye infection. Mosquitoes can infect a number of birds after a single feeding on a bird infected with fowl pox virus.
4. In a contaminated environment, presence of virus in the air from feathers and dried scabs containing fowl pox virus, may cause skin and respiratory tract infection. The virus can survive in dried scabs for months or even years.
5. Bad sanitary and hygienic conditions help in the spread of the disease.
Symptoms
Fowl pox can occur at any age. There are two forms of the disease: (I) skin or cutaneous form (dry pox), and diphtheritic form (wet form).
In the skin form, lesions (changes) appear on the unfeathered skin of the head, neck, comb, wattles, eyelids, legs, and feet. The lesions on the head, combs, and wattles are usually wart-like (nodular) in appearance, and yellow to dark brown in colour .
In the diphtheritic form (wet form), small white nodules are observed in upper respiratory and digestive tracts. These nodules merge together to form raised-yellow white cheesy patches. Most lesions are found in the mouth, but may also be present in the larynx, trachea, and oesophagus. These lesions cause difficulty in breathing. Recently it has been found that most cases of diphtheritic fowl pox are characterized by the formation of massive yellow cheesy necrotic masses in the larynx and adjacent trachea . The bird in such cases dies suddenly from asphyxiation (lack of oxygen). Lesions in the nares (nose) give rise to nasal discharge, while those on the conjunctiva to eye discharge.
Fowl pox usually causes weakness and poor weight gain. In layers, egg production is temporarily stopped.
Mortality is low (I to 2%) when skin lesions are present, but may be as high as 50% with the diphtheritic form , but is usually low.
Diagnosis
Wart-like lesions of the head particularly of the comb and around the eyes, or yellow cheesy lesions in the
larynx and adjacent trachea on postmortem, are diagnostic of fowl pox.
Treatment
There is no satisfactory treatment.
Control
I. Fowl pox can be prevented by vaccination . Therefore, preventive vaccination using a live vaccine is the most successful control method. Even when an outbreak of fowl pox has been diagnosed, it is advisable to vaccinate the flock immediately to stop further spread of infection.
2. Precautions should be taken to minimize the spread of the vaccine virus, both on the birds and in
the environment. Being a live virus, it is capable of spreading the disease and therefore must be handled carefully.
3. Carcasses of dead or affected birds should be buried or burnt. After removal of the birds the house
should be thoroughly disinfected, although the virus remains in the infected scabs and is difficult to clear from certain premises.
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