Brucellosis, Biology


It is also called as Bang's disease or contagious abortion as it causes abortion in late pregnancy and infertility.

Etiology: It is caused by gram-negative, non-motile and non-sporulating organism Brucella abortus in cows and buffaloes. The disease has zoonotic importance as dairy workers, veterinarians or butchers may pick up infection by handling the infected foetal membrane, uterine discharge or aborted foetus.

Pathogenesis: After gaining entry, the organisms are localized in the surrounding lymphnodes. 

Clinical signs: The symptoms are primarily based on the immune status of animal. Highly susceptible pregnant cows or buffaloes suffer from abortion after 6 months of pregnancy, retained placenta and metritis. In bulls, epididymitis and orchitis occur involving one or both the scrotal sacs. The testicles are enlarged and reveal painful swellings. Later on, testicles reveal liquifactive necrosis and are degenerated. In mild cases, synovitis and painful swelling of affected joint are noticed. Animals show painful movement with involvement of hock, stifle or knee joints. Though the mortality rates are low, but on postmortem examination, edematous placenta, leathery plaques on chorion and necrosis of cotyledons are observed.

Diagnosis: The disease is diagnosed by the history of abortions and clinical signs, and confirmed by isolation of causal organisms from visceral organs and lymphnodes of aborted foetus. The organisms can be stained with Ziehl Nelsons staining technique. Postmortem lesions in dead cases also confirm the disease. It can also be confirmed by performing agglutination test using commercially available coloured or plain antigen. Coloured antigen is used for plate agglu­tination test while for tube test, plain antigen is used. The disease can also be diagnosed by testing milk by ABR test using coloured-antigen.

Brucellosis can be easily differentiated from trichomoniasis and vibriosis as the later diseases are associated with low abortion rates in early pregnancy. In infectious bovine rhinotracheitis, foetus is autolysed and in listeriosis, foetus is normal and there is septicemia. Leptospirosis can be differentiated due to occurrence of haemoglobinuria and yellow-brown-coloured placental cotyledons.

Treatment: The treatment is difficult since organisms can multiply and remain alive in macrophages. Long acting oxytetracycline (20 mg/kg body weight) along with streptomycin (20 mg/kg body weight) given by intramuscular route for 5-7 days, are useful in treating the cases. Chloramphenicol @ 1 g/100 kg body weight for 10-15 days is found effective. Sulpha drugs, penicillin or streptomycin alone are of little value in its treatment. Control: The animal can be vaccinated with Brucella abortus cotton strain 19 vaccine. It is a live vaccine given @ 5 ml dose subcutaneously in 3-6 months old female calves. The same dose of vaccine can be given in adults if it is highly desirable but pregnant animals in advanced stage of pregnancy should not be vaccinated. Usually, vaccination in adult animals is not desirable as organisms are excreted in milk and interfere with agglutination test results and give false positive reaction. Greatest care must be taken in handling disposal of aborted foetus, foetal membranes and uterine discharge, etc. as it may spread the infection to human beings or other animals.

Posted Date: 9/19/2012 1:33:32 AM | Location : United States

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