Tuberculosis

Last revised by Henry Knipe on 18 May 2024

Tuberculosis (commonly abbreviated to TB, short for tubercle bacillus) encompasses an enormously wide disease spectrum affecting multiple organs and body systems predominantly caused by Mycobacterium tuberculosis. A small proportion can also be caused by Mycobacterium bovis through drinking unpasteurised milk or through close contact with infected cattle, bison, deer or elk and other cervids.

After COVID-19, tuberculosis (TB) is the leading lethal infection worldwide, killing 1.3 million people in 2022. About one-quarter of the world population has been infected, but only about 5-10% develop the disease. TB disproportionately affects people living in low- and middle-income countries, and people with HIV/AIDS are about 16 times more likely to contract TB. An estimated 5% of HIV patients have M. tuberculosis infections, which become clinically apparent when CD4 T-lymphocyte counts drop to below 350 cells/mm3. These patients present with atypical patterns such as normal chest radiograph, lymphadenopathy or pleural effusion. Cavitation is uncommon because it involves a delayed-type hypersensitivity reaction and strong lymphocyte reactivity to M. tuberculosis antigen 7.

Cavitating post-primary tuberculosis in humans is the primary source of transmission 8.

Multi-drug resistant TB (MDR-TB) is a major and increasing global health threat. Only about 40% of such cases receive treatment.

Clinical presentation will depend upon the morphology of infection and location. These are discussed in separate articles. 

Aristotle is usually credited as being the first to recognize the contagious nature of the disease. Discovery of the specific infectious agent, the tubercle bacillus (Mycobacterium tuberculosis), did not occur for several millennia until it was isolated by Robert Koch in 1882 4. M. tuberculosis was previously known as Koch bacillus and tuberculosis known as Koch disease 5. It was also historically known as consumption due to the severe associated weight loss, i.e. the disease "consumed", or ate up, the body ref.

The first trial of the first antibiotic treatment for tuberculosis began in 1946 ref. Streptomycin was discovered by Alfred Schatz and Elizabeth Bugie and gained the Nobel prize for their supervisor ref.

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