Gangrene is the invasion and decay of necrotic tissue by bacteria. It most commonly affects the lungs, intestines, mammary glands, and extremities. There are two main types - dry gangrene occurs when circulation is cut off in extremities, resulting in mummified tissue. Moist gangrene happens in organs with more moisture and heat, allowing bacteria to rapidly spread and cause sepsis. Specific forms include gas gangrene caused by Clostridium bacteria entering wounds and producing toxins.

1. Gangrene
Dr. Jeny K John
Asst. Professor (Veterinary Clinical Pathology)
Sardar Vallabhbhai Patel University of Agriculture and
technology,
Meerut

2. Gangrene
• It is the invasion and putrefaction of necrotic tissue by saprophytic bacteria
• Seen most often in the lungs, intestine, mammary gland, heavy muscles of
the thigh and shoulder and the extremities
1. Lungs:
Most commonly from the faulty drenching of medicines, improper insertion
of the stomach tube, paralysis and infectious diseases of the throat
2. Intestine:
Horse infarction results from a verminous thrombus in the anterior mesenteric
artery, or acute local passive hyperemia associated with a malposition of the
viscera
Vascular disturbances……necrosis………..invaded by saprophytic
bacteria…..gangrene

3. 3. Extremities
• Gangrene of the leg, ear, tail, wattle or comb is associated with
freezing
• Freezing….coagulative necrosis…..bacterial invasion….gangrene
• Certain drugs or plants (ergot and mould on fescue grass) cause
ischemia due to arterial spasm and restriction of blood flow
• Senile gangrene due to arteriosclerosis
• Diabetic gangrene-high sugar favour bacterial growth

4. • Gangrene is of two types: dry gangrene and moist gangrene
• Whether dry occurs or moist, depends on the amount of moisture as
well as temperature of the tissue
• When the coagulative necrosis is dominant, the process is dry
gangrene and when the liquifactive necrosis is more pronounced, it is
moist or wet gangrene

5. 1. Dry Gangrene
• Usually observed in extremities
• When necrosis occurs, circulation is no longer maintained.
• Necrotic tissue gets dehydrated by evaporation and become dry.
• Temperature and moisture content in extremities is less, so spread of
bacteria is slow

6. Macroscopically
• Area is dry, shriveled and appears mummified as a result of dehydration
• It is reddish brown, green, grey or black in colour (due to Fe sulphide)
• Bacterial putrefaction of the dead tissue produces hydrogen sulphide. When
hydrogen sulphide comes in contact with Fe of Hb- Fe sulphide is produces
• Pseudomelanosis due to black discoloration
• Putrid odor due to hydrogen sulphide
• Dead tissue is demarcate sharply from the living by a line of severe inflammatory
reaction
Microscopically
• Structure less necrotic area stained pink is seen with numerous bacteria
• A few gas bubbles are evident by clear spaces
• An acute inflammatory reaction is present at the junction of the living and dead
tissue

7. Moist gangrene
• Occurs in the internal organs where there is an abundance of moisture
and temperature is higher
• With optimum conditions of moisture and warmth, the growth and
spread of saprophytic bacteria are very rapid
• When the intestinal wall get necrotic, rupture occurs and fecal content
are discharged into the peritoneal cavity, spreading microorganisms
throughout the viscera.
• Course of events is extremely rapid and death occurs from septicemia,
toxemia and shock

8. Macroscopically
• Gangrenous tissue is moist and red, green, grey or black in colour as a
result of iron sulphide formation
• Odor is extremely offensive due to hydrogen sulphide
• Putrefaction produces gas and numerous gas bubbles are present
within the tissues
• Intestine is distended with large quantities of gas
• No sharp line of demarcation between the living and dead tissue

9. Gas gangrene, Malignant oedema and black quarter
• Specific type of moist gangrene frequently observed in animals and due to the
invasion of tissue by various clostridial organisms (Cl. perfingens, C. chauvoei,
C. septicum, C novyi)
• These organisms are inhabitants of soil and the digestive tracts
• They enter into wounds of various types. The injury to tissues results in necrosis
and in this necrosis tissue organisms grows and multiply
• They produce toxins that kill the surrounding tissue
• They then invade the necrotic tissue, spread through out the body and bring
about the death
• Seen in BQ and malignant odema