Tuberculosis in animal is caused by Mycobacterium bovis, M. tuberculosis and M. avium and among these the most important causal agent is M. bovis. The disease is characterized by development of tubercles in various organs.
Etiology: Mycobacterium bovis is an acid fast, non-sporulating, non-motile bacillus. The organisms can be killed by direct sunlight exposure or application of 2-3% cresol. It can produce disease in all animals and man of all age groups.
Pathogenesis: The organisms localizes in local lymph nodes and mucous membrane after inhalation or ingestion. The organisms develop there and primary lesions are formed after calcification. These are referred as tubercles or primary foci. The microbes spread from the primary foci to the regional lymph nodes. Nodular lesions in different organs, acute miliary tuberculosis or chronic tuberculosis of vital organs, may develop after spread of infection from primary foci.
Clinical signs: Progressive weakness, low grade fever, inappetance, chronic coughing and dryness of skin are the common clinical signs in cows and buffaloes. The coughing is pronounced after exercise, in cold weather or upon pharyngeal palpation. Later on, animals show dysponea or recurrent mild bloat and pleurisy. If organisms reach in the udder, mastitis develops.
In pigs, the disease occurs in localized form and non-progressive abscesses develop in lymph nodes of cervical area which rupture outside the body. In sheep and goats, bronchopneumonia, coughing and respiratory distress are common. In goats, intestinal ulcerations, enlargement of lymph nodes of gastrointestinal tract and diarrhoea are noticed. Osteomyelitis of cervical vertebrae, stiffness of neck, coughing, polyuria, mild fever, nasal discharge and enlargement of lymph nodes frequently occur in horses.During postmortem examination of dead animals, tuberculous granulomas were found in lymph nodes. Lungs reveal miliary abscesses and bronchopneumonia.
Diagnosis: It is diagnosed by the clinical symptoms, postmortem lesions of dead animals, and by performing tuberculin testing. Single or double intradermal, stormont or comparative tuberculin or short-thermal tests are useful in its diagnosis. Stormont test is superior as it can be employed for initial herd screening in advanced cases of tuberculosis, recently parturiated animals, suspicious reactors as well as in animals with paratuberculosis or avian tuberculosis. The disease can also be confirmed by serological tests like agglutination, complement fixation and fluorescent antibody tests.
Tuberculosis should be differentiated from traumatic reticulitis, aspiratory pneumonia and contagious bovine pleuropneumonia. In case of traumatic reticulitis, there is severe illness with leukocytosis and neutrophilia. The cases of aspiratory pneumonia had a history of faulty drenching while in contagious bovine pleuropneumonia, pleuritic friction sounds and expiratory grunts are common.
Treatment: The treatment is costly as animals are to be given combination of drugs for long periods. In bovines, use of 2.5 g streptomycin intramuscularly, 1.5 g rifampicin and 2g isoniazid orally are effective. This combined therapy should be given for about 4-6 months depending on the condition of animal.
Control: The control of disease is based on 3 principles - (i) removal of infected animals, (ii) prevention of spread of infection, and (iii) avoidance of further introduction of disease.