Bacterial skin infections - Pathology


Cutaneous bacterial infections tend to be called pyodermas. They are superficial, deep and are common in dogs, but less common in other species.


Superficial Pyoderma

Superficial pyoderma in a dog (Courtesy of Bristol BioMed Image Archive)
  • Affects epidermis and upper infundibulum of hair follicles
  • No scarring when healed
  • Grossly:
  • Microscopically:
    • Intraepidermal pustular dermatitis
    • Superficial suppurative folliculitis
    • Bacteria commonly not seen


Impetigo

Dermatophilosis

Greasy pig disease

Ovine Fleece Rot

Equine Pastern Folliculitis


Deep pyoderma

Staphylococcal Folliculitis and Furunculosis

Subcutaneous Abscesses


Bacterial Granulomatous Dermatitis

  • Usually due to saprophytes
  • Grossly:
    • Diffuse or nodular lesions
    • May ulcerate and form drainage fistulas
  • Microscopically:
  • Mycobacterial granulomatous or pyogranulomatous lesions
    • Usually caused by Mycobacterium lepraemurium (feline leprosy) or other Mycobacteria
    • Most commonly lesions appear on head, neck and legs
  • Botryomycosis

Bacterial Pododermatitis


Systemic Bacterial Infections

  • Salmonellosis
    • Capillary dilatation and congestion -> cyanosis of external ears and abdoman
    • Thrombosis -> necrosis of extremities
  • Erysipelas in pigs
    • Caused by Erysipelothrix rhusiopathiae
    • Vasculitis, thrombosis, ischaemia -> cutaneous lesions - firm, raises, rhomboidal pink to dark purple areas
  • Clostridium novyi
    • Severe cellulitis, toxaemia and death of young rams during breeding season (due to traumatised heads) - 'big head'
  • Streptococcus equi
    • In horses
    • Immune complex vasculitis -> purpura