anthrax ănˈthrăks [key], acute infectious disease of animals that can be secondarily transmitted to humans. It is caused by a bacterium (Bacillus anthracis) that primarily affects sheep, horses, hogs, cattle, and goats and is almost always fatal in animals. The bacillus produces toxins that kill cells and cause fluid to accumulate in the body's tissues.

Anthrax spores, which can survive for decades, are found in the soil, and animals typically contract the disease while grazing. Transmission to humans normally occurs through contact with infected animals but can also occur through eating meat from an infected animal or breathing air laden with the spores of the bacilli. The disease is almost entirely occupational, i.e., restricted to individuals who handle hides of animals (e.g., farmers, butchers, and veterinarians) or sort wool.

In the cutaneous, or skin, form of the disease, which is not usually fatal to humans, the bacillus enters the skin through a scratch, cut, or sore. Pustules occur on the hands, face, and neck; if the disease is not treated with antibiotics, the bacteria can migrate to the blood vessels, causing septicemia (blood poisoning) and death. Gastrointestinal anthrax is more likely to be fatal. Nausea, vomiting, and fever can be followed by abdominal bleeding, tissue death, and septicemia. Pulmonary, or inhalation, anthrax begins with flulike symptoms and ultimately causes lesions in the lungs and brain. It is rarer, but is usually fatal if not treated early. Because of this, individuals without symptoms who have been exposed to inhaled anthrax are treated with antibiotics for 60 days, anthrax vaccine, and other measures.

Anthrax is a well-known, ancient disease; the fifth plague visited upon the Egyptians in Genesis (see plagues of Egypt) resembles the disease. Pure cultures of the anthrax bacillus were obtained in 1876 by Robert Koch, who demonstrated the relationship of the microbe to the disease. Confirmation of the bacillus as the cause of anthrax was provided by Louis Pasteur, who also developed a method of vaccinating sheep and cattle against the disease. Anthrax is now uncommon in the United States because of widespread vaccination of animals and disinfection of animal products such as hides and wool.

Anthrax spores have been used experimentally by various nations as a biological warfare agent, but effective delivery of anthrax to a population is difficult, and such use is now banned by international convention. Because anthrax has been tested as a biological weapon, the United States has developed a vaccine for military use, but it requires several injections and annual boosters. An accidental release of anthrax from a military laboratory near Sverdlovsk (now Yekaterinburg) in the Soviet Union resulted in 68 deaths from pulmonary anthrax in 1979. In 2001 a number of people in the United States were exposed to spores that were sent through the mails and contracted anthrax; several persons died. Although these bioterror attacks occurred shortly after the terrorist attacks on the World Trade Center and the Pentagon, it did not appear to be linked to them.

S. D. Jones, Death in a Small Package (2010).

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