Bacterial skin infections - Pathology

From WikiVet English
Jump to navigation Jump to search


WikiPathWikiPath Banner.png
()Map INTEGUMENTARY SYSTEM (Map)
SKIN INFECTIOUS



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
    • Granulomatous dermatitis caused by nonfilamentous bacteria
    • Usually Staphylococcus aureus
    • Small, yellow granules are formed - sulfur granules
      • Central bacteria surrounded by homogeneous eosinophilic material
  • Filamentous bacteria can also cause granulomas

Bacterial pododermatitis

  • Digital infections in ruminants
  • Contagious footrot
    • Usually caused by Bacteroides nodosus together with Fusobacterium necrophorum
    • Moisture and trauma allow B. nodosus to enter -> aids bacterial penetration of epidermis -> F. necrophorum invades -> necrosis and inflammation
    • Grossly:
      • Early lesions - red, moist, swollen, eroded interdigital skin
      • Spreads to epidermal matrix of hoof -> separation of horn + malodorous exudate
      • Regeneration attempted as germinal epithelium is not destroyed
      • Chronic infections -> long , misshapen hoof
    • Benign footrot (scald)- only interdigital ski affected, slight separation of heel horn
      • Mostly the type occuring in cattle
  • Necrobacillosis of the foot
    • Usually caused by Fusobacterium necrophorum with other bacteria
    • In sheep:
      • Ovine interdigital dermatitis
        • Acute necrotising dermatitis similar to benign footrot
      • Foot abscesses
        • Bulbular or lamellar
        • Mostly in wet conditions and in heavy sheep
    • In cattle:
      • Interdigital dermatitis and cellulitis
      • Caused by F. necrophorum and Bacteroides melaninogenicus
      • Predisposed by trauma
      • Grossly:
        • Fissures, necrotic swollen edges in interdigital spaces
        • Inflammation may spread to joint spaces

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