Dermatophilosis

Description

A group of diseases caused by Dermatophilus species.Causes a range of conditions in large animals includin rain scald in horses and strawberry foot rot in sheep.

Clinical signs

• Caused by Dermatophilus congolensis
  • 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

Dermatophilosis in a cow (Courtesy of Bristol BioMed Image Archive)

• Caused by Dermatophilus congolensis
• Affects cattle, horses, sheep mainly
• More common in wet and warm weather
• Transmotted from animal to animal
• Lesions tend to form on dorsal back and extremities
• Associated with skin trauma, prolonged wetting or parasites
  • -> penetration of zoospores
• Bacteria proliferate in outer sheath of hair follicles and superficial epidermis
• Gram-positive, filamentous branching organisms, subdivided longitudinally and transversly
• Causing:
  • Acute inflammatory response -> neutrophil migration through dermis and epidermis -> formation of microabscesses
  • Further penetration of bacteria is thus prevented
  • Regenerated epidermis is invaded again by remaining organisms
  • Repeated reinfection -> multilaminated pustular crusts
• Grossly:
  • Papules, pustules, crusts may coalesce and mat the coat
• Microscopically:
  • Hyperplastic superficial perivascular dermatitis
  • Multilaminated crusts, alternating keratin and inflammatory cell layers