Anthrax is an infectious disease caused by bacteria that can survive for years as spores. It is usually found in animals, such as cattle, sheep, and goats. Although human cases are uncommon in the United States, people can get anthrax by inhaling spores from infected animals or animal products. Anthrax leads to breathing problems, serious illness, and often death. In 2001, anthrax spores were deliberately spread through the U.S. mail. The release of a large amount of anthrax spores into the air could harm many people, so terrorists could use anthrax in an attack. It is uncertain what would be the best way to protect people in such an attack. Antibiotics can help reduce serious anthrax illness, but they must be given early because the disease worsens rapidly. A vaccine for anthrax is available, but public health officials are reluctant to vaccinate the general population because of the vaccine's side effects and costs.