Dermatophilus congolensis

• 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
  • Disease most prevalent in young animals
  • Damage to the skin predisposes to infection; blood-sucking insects also thought to be involved in transmission
  • Lesions after heavy rainfall predominantly affect dorsum of farm animals
  • Papules, serous, exudative matting of hair, raised crusty scabs
  • Scab formation more prominent in sheep and cattle than in horses
  • Lesions may resolve within weeks if dry weather, or may progress
• Treatment:
  • Parenteral antibiotics e.g oxytetracycline, pr penicillin-streptomycin combinations