Synonym: BlacklegBlack-quarter (BQ) is an acute infection but a non-contagious disease characterized by inflammation of skeletal and cardiac muscles, severe toxaemia and high mortality in cattle, buffaloes and sheep.The causative agent is Clostridium chauvoei, a gram-positive anaerobic spore-forming rod-shaped organism. Less frequently other clostridial species have also been incriminated, which include Cl. septicum, Cl. novyi and Cl. sordellii. Mixed infection with Cl. septicum and Cl. chauvoei also occur. The spores of these organisms are highly resistant to environmental changes and disinfectants, and persist in soil for many years. The spores are resistant to weak disinfectants but are killed by coal tar disinfectants, 3% formalin in 15 min and bichloride of mercury in 10 min.
Transmission: In cattle, the disease is confined to young stock between the age of 6 months and 2 years. Buffaloes usually suffer from a mild disease. The outbreaks of BQ occur with the onset of rainy season. Cattle acquire infection from ingestion of organism and the ingested bacteria remain as dormant spores in tissues until predisposing factors stimulate the development of vegetative forms and rapid multiplication and formation of toxins. The contamination of soil and the pasture may occur from the infected faeces or decomposition of carcasses of animals dying of the disease. The disease in sheep is associated with history of wounds and trauma associated with ploughing, lambing, docking, castration and shearing.
Symptoms: Sometimes animals may die without showing symptoms. The most obvious sign is a crepitant swelling in hind or forequarters which crackles when rubbed due to gas in the muscle. The symptoms are fever, lameness and twitching of the muscles of the affected region. Death usually occurs within 24 hours of the symptoms first observed. The affected region is hot and painful but soon becomes cold and painless, and there is crepitation due to gas. The skin over the affected area becomes dry, hard and dark. Sometimes the muscle of neck and back is affected in sheep. High fever, anorexia and depression along with sudden death may be observed. The location of lesion corresponds to the original injury. In ewes, lesions develop in perineum after parturition.
Lesions: In cattle, when the limb is involved the carcass is found laying on the side with affecting leg stiff and extended. Bloating and putrefaction occurs soon and there is frothy blood-stained exudate from nostril and anus. Incision of lesion reveals that muscle is dark, black and spongy. The central lesion is surrounded by dark, oedematous swelling with gas bubbles giving a rancid smell. The body cavities contain excessive blood-stained fluid. Regional lymph nodes are enlarged. The body cavities are full of fibrin containing blood stained fluid. In sheep the muscle lesions are somewhat localized and the subcutaneous oedema is also less.
Diagnosis: The history, symptoms and lesions may be strongly suggestive of black- quarter. The central part of the lesion is black or dark red, necrotic and filled with gas bubbles. The affected muscle has a characteristic rancid smell. In less typical cases the diagnosis should be based on laboratory examination.Musc le im p ressio n sm ea r: Staining by Gr ams me thod would r eveal the characteristic spores. Muscle pieces could be used for biological test in guinea pigs which are inoculated with an irritant like calcium chloride before inoculation of the muscle extract would result in reproduction of the disease.
Treatment: Penicillin and tetracyclines if given in normal therapeutic doses promptly and inoculated into the site of lesion are of value. Large doses are required to be administered. Sulphathiozole and specific antitoxic sera are also effective. There may be success in cure by using antibiotics at the appropriate time as the organisms are highly susceptible to antibiotics.
Control: Hygiene and prophylaxis are the methods of control. Proper hygiene requires cleaning and treatment of all wounds and the destruction of carcases by burning. Active immunization of animals has proved to be effective. The vaccine used is formalinized alum precipitated whole culture Cl. chauvoei and Cl. septicum vaccine. It is a common practice to vaccinate animals before the onset of rainy season. Revaccination is recommended to attain immunity. In sheep vaccination prior to lambing or castration and docking is a useful precaution. During outbreaks, vaccination along with the administration of antibiotics is recommended.