The disease is caused by Mycobacterium tuberculosis, a rod-shaped bacterium. Symptoms of TB include coughing, chest pain, shortness of breath, loss of appetite, weight loss, fever, chills, and fatigue. Children and people with weakened immune systems are the most susceptible; half of all untreated TB cases are fatal.

In most cases, inhaling tiny droplets of moisture that contain the Mycobacterium tuberculosis bacterium infects a person. These droplets form when a person sick with TB coughs, sneezes, or speaks. Small particles carrying two to three bacteria surrounded by a layer of moisture are released into the air. "A sneeze may release as many as forty million microscopic droplets. There can be hundreds of bacilli in

a single drop." (Tuberculosis, p.38) When the other person inhales these particles, the bacteria may lodge into that person's lungs and multiply.

If the bacteria are multiplied, active primary tuberculosis will develop. Symptoms include coughing, night sweats, weight loss, and fever. A chest X-ray may show shadows in the lungs or fluid collection between the lungs and its lining. If the bacteria are inhibited, rather than destroyed, the immune cells and the bacteria form a mass known as a tubercle. In effect, the immune cells form a wall around the inactive bacteria. As long as the immune system remains strong, the TB bacteria will remain walled off and inactive. These initial tubercles in the lungs usually heal, leaving permanent scars that appear as shadows in the chest X-rays. At this initial stage, the disease does not progress, but the bacteria may remain dormant in the body for many years. If the immune system becomes weakened, the tubercle opens, releasing the bacteria and the infection may develop into secondary TB.

Although this disease was once ranked the most common cause of death in the world, it has come a long way. Today improved methods of prevention, detection, diagnosis, and treatment have greatly reduced the number of people who get the disease and the number of people who die from it. However, tuberculosis remains a major concern in developing countries where these improved methods are not widely available

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