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Canadian Public Health Association

What is tuberculosis?

Tuberculosis (TB) is an infectious disease caused by bacteria, called tubercle bacillus.

Tubercle bacillusTubercle bacillus

It is spread through the air when someone with active TB coughs or sneezes. It usually takes multiple exposures to catch tuberculosis.

People can carry the bacterium in its inactive form for years (inactive TB). If they are not treated with antibiotics, the bacteria can become active if and when the body's immune system can no longer contain the bacteria.

Active tuberculosis destroys the lungs and other parts of the body. Tuberculosis used to be called "consumption" because of the way the disease eats away at the body.

Malnutrition, old age, and diseases such as AIDS weaken immune systems and increase the risk of the bacteria growing.

Infants, adolescents and young adults are also more at risk because their immune systems are still developing.

TB doesn't just attack the lungs. The bacteria can also take hold in the lymph nodes, kidneys, bones, joints, larynx and central nervous system.

The disease can also be spread by consuming milk from a cow that has TB. Before the mandatory pasteurization of milk in Canada, bovine tuberculosis was a common cause of death in children under age five. (For more about this, see The Story of Milk.)

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