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.

Usually due to saprophytes
Grossly:
- Diffuse or nodular lesions
- May ulcerate and form drainage fistulas
Microscopically:
- Macrophages +/- multinucleated giant cells
- Caseous necrosis and neutrophils
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

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