Anthrax is an infection that is caused by the bacteria Bacillus anthracis. These bacteria form spores that are hard-shelled, dormant versions of the bacteria. Spores are the form of the bacteria that cause infection. They can survive in the soil for many decades.
Anthrax most commonly occurs in animals such as pigs, cattle, horses, and goats, but it can also infect people. Infections in people are caused by contact with the spores through a cut or scratch in the skin (known as cutaneous anthrax), by inhaling the spores (known as inhaled or pulmonary anthrax), or by eating meat that contains the spores (known as intestinal anthrax).
In biological warfare, anthrax can be transmitted intentionally through the air or by contact with an object that has the bacteria on it. Anthrax cannot be passed from one person to another (i.e., it is not contagious).
Symptoms of cutaneous anthrax appear almost immediately, up to one day after infection, whereas pulmonary anthrax symptoms usually appear 2 to 6 days after infection, but may take 6 weeks or longer to show up. Symptoms of intestinal anthrax appear in about 1 to 7 days.