BLACK LEG DISEASE MADE BY Riham Mostafa Nancy alarabawy

Def: Also called black quarter, an infectious, often fatal disease of cattle and sheep, characterized by painful, gaseous swellings in the muscles, usually of the upper parts of the legs cause:- Clostridium chauvoie a rod shape gram positive, motile, sporulating non capsule forming anaerobic microorganism. Clostridium chauvoie produces four toxin which is both necrotizing and hemolytic.

R.O.I:- The spores probably are ingested, pass through the wall of the GI tract, and after gaining access to the bloodstream, are deposited in muscle and other tissues (spleen, liver, and alimentary tract) and may remain dormant indefinitely.

Pathogenesis : Cattle ◦ blackleg infection is endogenous. Lesions develop without any history of wounds, although bruising or excessive exercise may precipitate disease in some cases. Commonly, the animals that contract blackleg are of the beef breeds, in excellent health, and gaining weight. ◦ Outbreaks occur in which a few new cases are found each day, sometimes for several days. Most cases are seen in cattle from 6–24 mo old, but thrifty calves as young as 6 wk and cattle as old as 10–12 yr may be affected. Sheep ◦ the disease is almost always the result of a wound infection and often follows some form of injury such as shearing cuts, docking, crutching, or castration.

Pathogenisis : ◦ Spores by ingestion intestinal mucosa ----blood circulation and being carried to skeletal muscles and remaiming dormant. ◦ Under muscular fatigue or trauma to the muscle producing anaerobic conditions allow spores to activate.proliferate and produce toxins …app ◦ The toxins cause capillary damage.hemorrhagic edema and necrosis of myofibers with formation of gas (h2s) ◦ The organism is able to ferment sugar gangrene and toxemia.

PM: t he infected area is composed of black, dead (necrotic) muscle which is pocked with gas bubbles and is usually found in the heavier more active muscle masses of the animal. A sweetish odor of rancid butter may be detected from a fresh lesion. Lesions may occasionally be discovered in the diaphragm, heart or tongue

Two stages of the disease: ◦ Early stage : there is serohemorrhhagic exudates between necrosed muscles which appeared dark red. ◦ Late stage : the muscle has aporous appearance due to presence of gases with the presence of black discolortion due to formayion of iron sulphide ◦ Peticheal hemorrhages on the serous membranes. ◦ Parenchymatous degeneration ---due to toxemia ◦ Edema and hemorrhage on serous cavities.

Black leg. Dark-red skeletal muscle of a heifer showing hemorrhage, necrosis, edema and emphysema. : Black leg disease. Heart muscle showing dark red hemorrhagic and emphysematous

CLINICAL SIGNS :- 1.Lamness 2.Fever 3.Anorexia 4.Depression 5.Marked swelling of the upper part of affected leg 6.Skin over the swelling become discolored & dr

The animal dies within hours after the appearance of signs. Recovery case

GROSS PICTURE :- 1. The dead animal are usually lying on the affected side. The carcass is bloating and putrefaction quickly. The lesions usually involve hind quarters, shoulders, neck, back or lions and frequently tongue and heart 2. The skin over the affected area is dark red or even black with crepitating on pressure. The gas is due to formation of H2S and the black color is due to iron sulphide formation. In cut section a serosanguineous, foul smell fluid may exude.

3. The subcutaneous tissue is red or infiltrated with yellowish gelatinous exudate intermixed with hemorrhages and gas bubbles 4. The incised affected muscles are dark red in color, swell with rancid odor due to fermentation of glycogen (Figs 1&2).

5. The regional lymph nodes are enlarged and may be hemorrhagic. 6. The heart usually shows ulcerative endocarditis in the left atrium, bicuspid valve, and inner wall of the pulmonary vein. 7. Body cavities: The abdominal and thoracic cavities contain excess fluid which contains variable amounts of fibrin and is usually blood. stained. 8. Other organs: The internal organs undergo degeneration, and the postmortem decomposition with the production of gas in the liver occurs rapidly.

MICROSCOPIC APPEARANCE The muscle fibers show coagulative necrosis which infiltrated with neutrophils and lymphocytes, cloudy swelling, and fatty change. Moreover, the muscle fibers are separated by gas bubbles, edema, and hemorrhage Gram positive microorganisms are observed everywhere among the muscle fibers. The lymph nodes show hemorrhagic lymphadenitis and emphysema besides myocarditis and ulcerative endocarditis.

Lymph node of cattle infected with black leg disease showing air bubbles (emphysema). H&E.

Refrences : ditions/clostridial_diseases/blackleg.html cattle/ the book of clinical vetrinary pathology cairo university es4.html