The Condition

Favus is a chronic skin condition that afflicts poultry and mammals, including humans. It is normally caused by the dermatophytic fungus Trichophyton megninii. The fungi Microsporum gypseum and T. simii have also been identified with some cases of favus. It is not considered a particularly important disease of intensive poultry, although it may be a problem in some free-range and backyard flocks.

The first symptoms include the development of lesions on non-feathered skin, such as the lower leg, comb and wattle. Some loss of feathers and skin scales may occur although there are normally no significant signs.

The condition arises through the invasion by the T. megninii of the corpus lutuem of the skin. Lesions first develop on the comb and then the fungus may spread to produce white spots, giving the appearance of sprinkled flour. As the disease spreads concentrically, the white spots begin to scale off to give an appearance of a wrinkled crust. Although birds can recover from this, the fungus may spread to the feathered regions. When this happens, the feathers may fall out in patches and thickened, crusty skin develops around the feather follicles. These may develop as depressions and are often referred to as "favus cups".

Severe cases may result in the development of nodules and yellow caseous deposits in the respiratory tract.

Young birds with well-developed wattles are most likely to be affected.

Diagnosis of favus is by histological identification of hyphae or spores in skin lesions and feather follicles and by culturing the fungus on Sabouraud dextrose agar or selective dermatophyte media.