Favus :

• Also known as Avian Ringworm.
• Favus is chronic skin disease that affects poultry and mammals.
• Favus has a worldwide distribution but it’s occurrence has been sporadic .
• Disease is contagious and is transmissible in humans.

Etiology :

              Microsporum gallinae ( previously , Trichophyton gallinae )

• Incidence has been reported in chickens, turkey , duck , quail and conary .
• gallinae may be more common in backyard and game chicken flocks .
• Live in damp/ humid places .

Transmission :

• They are transmitted to chickens through direct or indirect contact with skin of other infected birds, animals, insects, people , soil or fomites ( equipment , object , clothes )

Pathogenesis :

 Hyphae ( Microsporum gallinae )

             ⬇

Stratum corneum ( comb, wattle, shanks )

             ⬇

Hyperplasia and hyperkeratosis

             ⬇ 

Infection – confined to epidermis

             ⬇

Minimal inflammatory reaction

             ⬇

Dry, white and scaly ( regress , static and progress )

             ⬇

Feathered areas ( depression around follicles )

 [Favus cups ]

Signs :

• White , powdery spots and wrinkled crusts and scab on comb and wattles
• Feather l;oss
• Honeycomb skin
• Thick crusty skin around head
• Loss of condition

Fig : Microsporum gallinae -positive cock showing white scaling on the comb.

Postmortem lesions :

• Hyperkeratosis of skin epithelium with invasion of stratum corneum by fungal mycelia
• Acanthosis ( brown-to-black, poorly defined, velvety hyperpigmentation of the skin)
• Acantholysis ( is the loss of intercellular connections, such as desmosomes, resulting in loss of cohesion between keratinocytes)
• Hydropic degeneration of cells in stratum spinosum

Microscopic lesions :

• The underlying deris was infiltrated by mononuclear cells and contained lymphoid foci.

Diagnosis :

• History
• Clinical signs
• Physical exams
• Cytology – skin scrapes

Fig : Acanthosis