Dermatophilosis

Description

A group of diseases affecting the epidermis caused by dermatophilus congolensis . Causes a range of conditions in large animals including rain scald in horses and strawberry foot rot in sheep. Lesions typically involve exudative dermatitis with scab formation.

Signalment

Can be seen in animals of all ages but most commonly occurs in young animals who are chronically exposed to moisture.

History and Clinical signs

Lesions commonly occur followng heavy rainfall and commonly affectsthe dorsum of animals. Any previous trauma or damage to the skin can predispose to infection. Blood-sucking insects are also thought to be involved in transmission.

Equine dermatophilosis Three clinical syndromes have been documented: rain scald, Mud fever and grease heel.

• • 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