- Filamentous, branching actinomycete
- Aerobic
- Produces motile zoospores
- No growth on Sabouraud dextrose agar
- Dermatophilosis most prevalent in tropical and subtropical regions
- Organisms found in scabs and in foci in skin of carrier animals
- Dormant zoospores become activated when moisture and temperature levels are favourable
- Zoospores may survive 3 years in scabs
- Pathogenicity:
- Does not usually invade healthy skin
- Entrance after trauma or persistent wetting
- Activated zoospores produce germ tubes which develop into filaments which invade the epidermis
- Invasion causes an accute inflammatory response with many neutrophils
- Microabscesses are formed in the skin
- Raised crusts develop in the affected regions
- Pathology
- Diagnosis:
- Giemsa-stained smears from scabs reveal branching filaments containing zoospores
- Immunofluorescence
- Scab material can be cultured on blood agar at 37 degrees centigrade, 2.5-10% carbon dioxide for 5 days
- Zoospores can be cultured
- After incubation, colonies are yellow and haemolytic (after 48 hours); they later become rough and yellow, and gain a mucoid appearance
- No growth on Sabouraud dectrose agar
- Clinical infections:
- Infection usually confined to epidermis
- Dermatophilosis