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 years.
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.
It is very rare that people get anthrax infection through natural causes. However, anthrax can be produced in laboratories and may be used as an agent of biological warfare. Anthrax is used in this manner because of the serious disease that results when the anthrax spores are inhaled. Inhaled anthrax often causes death if it's not treated in the early stages, which is why it is very important to recognize the symptoms of this infection (see "Symptoms and Complications").
The most common type of anthrax infection is cutaneous (on the skin) anthrax. In fact, this accounts for over 95% of naturally occurring anthrax infections. Cutaneous anthrax infection may take place when someone handles animals or animal products (wool or other woven materials) that are contaminated with anthrax, or if someone handles materials that have been intentionally contaminated with anthrax.
It is quite rare for meat to be contaminated with the bacteria that causes anthrax in North America. Therefore, intestinal anthrax is very rare on this continent.