The disease is otherwise known as black leg or emphysematous gangrene, and it is associated with severe toxaemia, emphysematous swelling of muscles, and crepitating sound on palpation of the affected muscles.
Etiology: The causative organisms, Clostridium chauvoei are gram positive spore forming rods. It is a soil-borne infection and spreads mainly through abrasions during docking, shearing, etc. The disease primarily occurs in cows, buffaloes and sheep, and is more common between 6 months to 2 years age group.
Pathogenesis: The spores germinate and liberate toxins in tissue after their entry. The toxin causes necrosis of muscles and toxemia. Excess gas accumulation in the affected muscles leads to production of crepitating sound on palpation.
Clinical signs: The presence of swelling in the muscles of shoulder, hip, chest, back or flank- region is main symptom of the disease. Initially, the swelling is hot and painful but later on it becomes very extensive, cold and painless. Crepitating sounds can be listened on palpation of swelling, Afterwards, the skin of that area becomes dark and dry. Dark colour froth mixed foul smelling fluid is released by puncturing the swollen area. Affected animal also shows the signs of reveal anorexia, ruminal stasis, high rise of body temperature and increased pulse rate. In terminal stage, diaphragm, tongue and heart muscles are also involved resulting in death.
Sheep usually suffer from mild form of the disease and there is stiff gait and lameness of one or more limb. Subcutaneous edema and gaseous crepitation are noticed only before death. High fever, anorexia and depression along with localized swellings are the common clinical signs.
In dead animals, putrefaction occurs very rapidly and there is severe bloat. Blood mixed frothy exudate comes out of nostrils and anus. In the peritoneum, haemorrhagic fibrinous exudate can be noticed. Dark-coloured fluid is released after incising the skin over affected muscles. The exudate has rancid odour and a metallic sheen.
Diagnosis: It is diagnosed by clinical sign in sick animals and confirmed by postmortem lesions in dead animals. It is also confirmed by isolation of the causal organisms. Serological and serum biochemical tests are also helpful in its confirmation.
The disease is differentiated from anthrax, bacillary haemoglobinuria, haemorrhagic septicemia, lead poisoning and sweet clover poisoning. In anthrax and sweet clover poisoning, crepitating swellings over muscles are absent while in bacillary haemoglobinuria, infarction of liver and haemoglobinuria are noticed. Haemorrahagic septicemia can be differentiated by the presence of swelling only in the pharyngeal region and absence of crepitating sound.
Treatment: Severe cases can be treated by giving BQ antisera and large doses of antibiotics. Antisera may be given @ 200-400 ml intravenously and is repeated after 24 h. Penicillin is highly effective against these organisms. Crystalline penicillin can be given @ 10 000 units/kg body weight by intravenous route followed by long acting penicillin by the intramuscular route. The treatment is continued for 5-7 days. Ciprofloxacin and norfloxacin are also effective against this disease.
Control: A polyvalent killed vaccine is given @ 5 ml subcutaneously before onset of rains. The animals are immune for 1 year. So, vaccination and proper disposal of carcass, either by burning or deep burial, help avoiding soil contamination and the occurrence of disease.