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Other Names: Infected Comb
All chickens have a fleshy comb on the top of their head (although it various in size, color, and shape depending on the breed). It is an outgrowth from the dermal and epidermal layers of the skin of the head. The comb is vulnerable to invasion with several fungal pathogens resulting in primary infection. Secondary bacterial infections may also occur, resulting from frostbite, injury or trauma, and fowl pox lesions. Some of the most frequent comb infections reported in chickens include:
Cutaneous mycosis or cutaneous candidiasis: A fungal infection caused by Candida albicans, resulting in crusty white circular patches or lighter diffuse areas on the comb. It may occasionally also involve the wattles, face, ear lobes, and/or neck. Some birds may also have small black scabs within a few lesions, and others may concurrently occur with hyperemia and feather loss in the surrounding areas.
Epidermoid cysts: Epidermoid cysts can occur on the chicken's comb. They appear as several firm, yellow, keratinized masses measuring 4-15 mm in diameter. They may be accompanied by infection with Aspergillus fumigatus and Alternaria spp.
Favus: Favus is the avian term for ringworm. The most common etiologic agent isolated is Microsporum gallinae. Infected birds develop white crusts or plaques on the comb, followed by feather loss starting at the caudal base of the comb and progressing down the neck. Histopathological lesions included hyperkeratosis of the skin epithelium with invasion of the stratum corneum by fungal mycelia, acanthosis, acantholysis, and hydropic degeneration of cells in the stratum spinosum.
Comb necrosis: Infection with Staphylococcus aureus and Pasturella spp resulted in total necrosis of the comb in one flock of hens who concurrently developed leg weakness. Histologically, liquefactive necrosis of epidermal epithelial cells with hyperplasia, vesicle formation in the epidermis, congestion, and hemorrhages with fibrinous thrombi of underlying dermis in the comb were noted. In mature comb lesions, the epidermis showed eosinophilic necrosis (scab formation).