General Veterinary Pathology

GANGRENE

Definition

• Gangrene is a necrotic area invaded by saprophytic organisms leading to putrefaction.

Types of gangrene

• There are three types of gangrene
  • Dry gangrene
  • Moist gangrene
  • Gas gangrene

Dry gangrene

Dry gangrene represents an area of coagulation necrosis resulting from infarction followed by mummification. The extremities of the body like tail, ears, legs and udder are affected.

• Causes
• Toxins (phytotoxins and ergotoxins): The toxins cause marked peripheral arteriolar vasoconstriction and damage to capillaries leading to thrombosis and infarction.
• Fescue poisoning
• Cold (Frost bite): Direct freezing and ice crystal formation leading to cellular damage, vascular damage and ischaemic necrosis.
• Gross pathology
• Affected part is dry (dehydration due to exposure to environment), shrivel (dehydration) and brown to black (due to formation of iron sulphide: iron from haemoglobin degradation, sulphide from putrefaction), proliferation of bacteria due to unfavourable environment, temperature and moisture.
• However, at the junction of living and dead tissue, there is a line of demarcation due to active inflammatory reaction.

Dry gangrene

Moist gangrene

• Causes: Intestine desplacements: Intususception, volvulus, incarceration
• Gross pathology
• The affected parts are soft, moist and reddish brown to black, foul smelling or putrid odour due to hydrogen sulphide, ammonia and mercaptanes. The environment is conducive for rapid growth of bacteria. There is no line of demarcation between live and dead tissue.

Moist gangrene - Intussusception

• Histopathology
• Initial coagulation necrosis with a few bacterial multiplications. Later liquified due to rapid proliferation of bacteria and infiltrating neutrophils.

Gas gangrene

Anaerobic bacterial proliferation producing toxin and damaging the tissues. Examples: Clostridium perfringens, Clostridium septicum introduced by penetrating wounds. The clostridia proliferate in necrotic tissue under anaerobic environment and produce toxins which cause tissue damage. The Clostridia chauvoei spreads haematogenously from the intestine and lodges in muscle which requires some injury and necrosis for the spores to germinate and bacteria to proliferate.

• Gross pathology
• Affected parts are dark red to black, contain gas bubbles, serosanguineous exudates and foul smelling.
• Histopathology
• Coagulative necrosis of muscle, bacteria, serosanguineous exudates and gas bubbles are seen