Bovine tuberculosis (bTB) is a chronic inflammatory disease of cattle caused by members of the Mycobacterium tuberculosis complex (MTC). While bTB is well-controlled in high-income countries, it remains endemic in most low- and middle-income countries (LMICs), where it continues to be a significant animal health problem that limits livestock productivity. The infection mainly affects the respiratory tract, resulting in lesions in the lungs, respiratory tract and associated lymph nodes, but can spread elsewhere. Due to the chronic nature of the disease, early infections are usually asymptomatic taking up to several months for clinical signs to manifest, whereas in the later stages, symptoms include progressive emaciation, weakness, inappetence and enlargement of lymph nodes. The disease also represents a significant threat to public health as the causative pathogens have potential for zoonotic transmission. The currently available OIE-recommended diagnostic tests for detection of bTB have several disadvantages, and there is also no licensed vaccine against bTB that is presently available.

Caused by

Bovine tuberculosis is caused by members of the Mycobacterium tuberculosis complex (MTC), primarily by M. bovis, M. caprae, and in certain parts of the world by M. orygis and M. tuberculosis. The MTC is a group of highly related pathogenic mycobacteria and more information about these pathogens can be found here.​

Clinical Signs

​The disease has a long incubation period and the animal may take several years to develop clinical symptoms, which typically include:

• Weakness
• Loss of appetite
• Progressive emaciation
• Diarrhea and weight loss
• Large prominent lymph nodes
• Fluctuating fever
• Laboured breathing
• Intermittent hacking cough

Early diagnosis is critical in the case of Bovine Tb.
Related information about symptoms can be obtained here. 

source: www.afrivip.org

Transmission

The disease is transmitted by:

• Close contact with diseased animals.
• Inhalation of infected aerosol droplets.
• Exudates from lesions like draining lymph nodes, urine, feces, milk, vaginal secretions, semen, etc.
• Drinking raw milk from infected animals.
• Contaminated feed, water, and fomites.

Movement of asymptomatic carrier animals prove to be an important cause of disease spread which can be controlled by early and prompt diagnosis. Further information regarding the transmission can be found here.

Treatment and Control

Treatment of infected animals is not cost effective in cattle due to the lengthy (4-12 months) antibiotic course required, and hence rarely attempted. Controlling the movement of animals in the suspected herd, isolation of suspected animals, avoiding overcrowding, and following standard hygienic practices on the farm can help reduce the risk of infection. Improved surveillance efforts through tuberculin skin testing, efficient laboratory diagnosis, post-mortem inspection, and a test and segregation strategy can be advantageous in low- and middle-income countries. Efficient diagnosis is crucial for preventing the spread of bTB. Related information about the control strategies can be accessed here.

Zoonotic Importance

Tuberculosis is caused in humans and cattle by closely related members of MTC and the transmission of MTC members from animals to humans is called zoonotic tuberculosis (zTB). The disease spreads to humans through direct contact with infected cattle, consumption of infected milk and undercooked meat products, and contact with infected tissues at butcheries or abattoirs. The control and eradication of zTB require prompt and early diagnosis of preclinical infection in animals, followed by the segregation of infected animals from the herd. ​Detailed information about the control of zTB can be obtained here.