Tuberculosis ("TB") is a wasting disease of the lungs caused by the bacterium Mycobacterium tuberculosis. In earlier times it was known as consumption.

People with an active case of the disease spray the bacterium into the air in tiny water droplets that can then be inhaled by others. Once in the lung, the body responds by confining the bacterium in granules, called tubercles. The person is infected, but shows no symptoms.

If the body's immune system grows weaker (as a result of another infection, stress, exertion, etc.) the bacterium can break out of the tubercles and spread.

The body now responds by killing bacteria and surrounding cells. Symptoms now appear: fever, night sweats, lack of appetite, followed by chest pain and a productive cough. In time, the sputum turns bloody.

TB is very widespread; it is estimated that about a third of the world's population is infected with it. Eight million people get active TB every year, and two million die from TB-related illness. It is probably the second-largest single cause of human death today.

Bottom line for the deep sea sailor: To prevent TB, make sure your boat (and the places you stay when ashore) has adequate ventilation. If you detect signs of infection, seek medical help immediately.