Bacillus anthracis, the organism that causes anthrax, derives its name from the Greek word for coal, anthracis, because of its ability to cause black, coal-like cutaneous eschars.

Anthrax infection is a disease acquired following contact with infected animals or contaminated animal products or following the intentional release of anthrax spores as a biological weapon.

In the second half of this century, anthrax was developed as part of a larger biological weapons program by several countries, including the Soviet Union and the U.S. The number of nations believed to have biological weapons programs has steadily risen from 10 in 1989 to 17 in 1995, but how many are working with anthrax is uncertain.

Perhaps more insidious is the specter of autonomous groups with ill intentions using anthrax in acts of terrorism. The Aum Shinrikyo religious sect, infamous for releasing sarin gas in a Tokyo subway station in 1995, developed a number of biological weapons, including anthrax.

Given appropriate weather and wind conditions, 50 kilograms of anthrax released from an aircraft along a 2 kilometer line could create a lethal cloud of anthrax spores that would extend beyond 20 kilometers downwind. The aerosol cloud would be colorless, odorless and invisible following its release. Given the small size of the spores, people indoors would receive the same amount of exposure as people on the street.

There are currently no atmospheric warning systems to detect an aerosol cloud of anthrax spores. The first sign of a bioterrorist attack would most likely be patients presenting with symptoms of inhalation anthrax.

A 1970 analysis by the World Health Organization concluded that the release of aerosolized anthrax upwind of a population of 5,000,000 could lead to an estimated 250,000 casualties, of whom as many as 100,000 could be expected to die.

A later analysis, by the Office of Technology Assessment of the U.S. Congress, estimated that 130,000 to 3 million deaths could occur following the release of 100 kilograms of aerosolized anthrax over Washington D.C., making such an attack as lethal as a hydrogen bomb. The Centers for Disease Control and Prevention estimates that such a bioterrorist attack would carry an economic burden of $26.2 billion per 100,000 people exposed to the spores.

The largest experience with inhalation anthrax occurred after the accidental release of aerosolized anthrax spores in 1979 at a military biology facility in Sverdlovsk, Russia. Some 79 cases of inhalation anthrax were reported, of which 68 were fatal.

One of the major problems with anthrax spores is the potentially long incubation period of subsequent infections. Exposure to an aerosol of anthrax spores could cause symptoms as soon as 2 days after exposure. However, illness could also develop as late as 6-8 weeks after exposure -- in Sverdlovsk, one case developed 46 days after exposure.

Further, the early presentation of anthrax disease would resemble a fever or cough and would therefore be exceedingly difficult to diagnose without a high degree of suspicion. Once symptoms begin, death follows 1-3 days later for most people. If appropriate antibiotics are not started before development of symptoms, the mortality rate is estimated to be 90%.

There are a number of rapid diagnostic tests for identifying anthrax at national reference laboratories, but none is widely available.

If anthrax is suspected on clinical, laboratory or pathology grounds, then the Working Group recommends that hospital epidemiologists contact local and state health officials immediately so that the proper reference tests can be performed.

The U.S. has a sterile protein-based human anthrax vaccine that was licensed in 1970 and has been mandated for use in all U.S. military personnel. In studies with monkeys, inoculation with this vaccine at 0 and 2 weeks was completely protective against infection from an aerosol challenge at 8 and 38 weeks, and 88% effective at 100 weeks.

However, U.S. vaccine supplies are limited and U.S. production capacity is modest. There is no vaccine available for civilian use.