Insects, contaminated food and water, sneezing, and unwashed hands are just some of the ways infectious diseases pass from one person to another. Communicable diseases cause significant health risks around the world, and new ones can appear at any time. They may follow a natural or manmade disaster, a bioterror attack, or a migration of groups of people from one geographical area to another. An international gathering could be a starting point for an outbreak. Some communicable diseases are preventable through vaccination; others are not.
One-third of the 7.7 billion people on Earth carry the tuberculosis (TB) bacterium. Coughing, speaking, or singing spreads this communicable disease through the air to others. The bacteria that causes TB attacks the lungs, but may also affect the spine, kidneys, and brain. There are two types of TB, and not everyone who is infected becomes sick or passes the disease on to someone else. Latent TB infections cause no symptoms and are not infectious. The only way to detect this version is a tuberculin skin test. TB disease may appear soon after the infection, or it may linger until the immune system becomes too weak to fight it off.
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