Fowl favus is a superficial, chronic, sporadic mycotic infection of birds caused mainly by Trichophyton gallinae. Very rarely Trichophyton simii is also involved in the aetiology of favus in fowl. The disease is world-wide in distribution. Human beings sometimes contact the infection from the affected fowl. Though the disease is contagious in nature, the reservoir of infection is not known. It is presumed that infection is introduced into a healthy flock by the purchase of sick bird. Young birds particularly chicks are most likely to be affected.
Symptoms: Initial lesions in the form of minute, pinhead size, white spots develop on the comb. Later scaling occurs which may involve wattles and unfeathered portions of the head. As the disease advances, scaly deposits may become thick and form crusted patches. In severe cases the infection spreads to feathered portion of the body. As a result, feathers are usually pulled out and shed off leaving a patch on the body. Sometimes chicks may show depression, anaemic, weakness and jaundice. The infection is confined to the keratinized tissues and does not invade the deeper organs. The fungus produces mild inflammatory reaction at the site of invasion.
Diagnosis: Clinical diagnosis is made on the basis of typical lesions on the wattles and comb. The scraping from the lesion may be examined for the presence of fungal spores and hyphae after treating with 10 % KOH for 30 min. The isolation of aetiological agent on appropiate media suitable for isolation of fungi from lesions confirms the diagnosis.
Treatment and prevention: affected bird should be sacrificed and disposed either by burning. The bird with mild infection should be isolated and treated regularly to limit the spread of infection. After removing the crust with soap and water, the lesion should be painted with tincture of iodine, 2 % formalin ointment and 5 % phenol solution. The infected poultry sheds should be cleaned and disinfected. As the disease is communicable to human beings, care should be exercised while dealing with sick birds.