Tuberculosis also known as TB, has existed since at least 2000 BC. The term tuberculosis was first used in 1839, and it is derived from the Latin word tubercula. Tubercula means a small lump, referring to the small scars seen in the tissues of infected individuals. "This potentially serious infection spread mainly through the air from one person to another. TB usually infects the lungs, but can also cause symptoms that affect the whole body." (Human Diseases and Conditions, p.875).
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.
"The body expels many inhaled tubercle bacilli before they can do harm. Some bacilli settle into the layer of mucus that lines most of the respiratory system, including the nasal passages and the tracheobronchial tree. The bacilli trapped in the mucus layer are moved up the airways toward the throat mouth and nose. The bacilli may then be sneezed, spat, coughed or blown out." (World Book, p.477).
There are two types of infections, Primary and Secondary TB. In Primary TB, a person has become infected with the TB bacteria but is often not aware of it.