The bacterium is relatively easy to culture and the spores are stable in storage under a wide range of conditions.

As an agent, it is expected that anthrax spores would be released at a strategic location to be inhaled.

The spores are very hardy and can survive superheated steam (159° C, 285° F) for 2 hoursand can contaminate soil and water for years or decades. Even though the spores are relatively hardy, they are killed in air by exposure to ultraviolet light. They die off with half lives of about 0.0-1.5 hours depending upon the cloud cover. A weapon system would require a few grams to a few kilograms in a payload. The infectious dosefor a healthy individual is fairly high, typically an individual has to inhale about 10,000 spores to have a 50% chance of dying of pulmonary anthrax (this is the LD₅₀ or lethal dose effective for 50% of the population), anthrax is much more lethal than a chemical weapon. That is, the mass of bacteria needed is far less than that required of a chemical weapon. One gram of B. anthracis contains about 100 million lethal doses, making it about 10,000-100,000 times deadlier than nerve agents. Information derived from fatalities in the anthrax mail attack of late 2001 forced a reassessment of the infectious dose. It is now believed that the infectious dose can be as low as a few tens of spores for the most vulnerable, such as the elderly or those with lung problems.

A 1970 estimate from the World Health Organization estimated that delivery of an aerosol of Bacillus anthracis over a city of five million would kill 100,000 and incapacitate a further 150,000.

Anthrax could be used against livestock as an economic weapon and to deny areas by soil contamination. It was actually used in this way by the white regimes of Rhodesia (now Zimbabwe) and South Africa as they battled against the coming of majority rule. Sporadic outbreaks of anthrax in herds owned by black Africans but not by white Rhodesians were the first sign that this was taking place.

Terrorist Acquisition and Attempted Use.

• The Baader-Meinhof Gruppe threatened to spread anthrax through the mails in West Germany in the 1970's
• In 1973 a German biologist threatened to contaminate water supplies with B. anthracis and Clostridium botulinum unless he was paid a ransom of several million dollars.
• In October 1981, protesters claimed to have taken B. anthracis-contaminated soil from Gruinard Island that would be delivered to the Microbiological Research Establishment at Porton Down.
• Prior to the 1994 Tokyo subway Sarin gas incident, Aum Shinrikyo is believed to have tried to attack the US embassy in Tokyo with B. anthracis but failed because they used a non-pathogenic vaccine strain of the organism.
• The agent exercises a fascination for militia groups in the US and one person (Larry Wayne Harris) has been arrested twice in the 1990's for illegal possession of B. anthracis.
• Over 200 anthrax hoaxes were perpetrated in the U.S. in the late 1990's when they took the place of the parcel and letterbomb hoax as a way of disrupting an organization. They later spread to Britain where anthrax hoaxes began to emerge in late 2001.
• A significant attack took place in the United States in October 2001. It began when Florida man died of inhalation anthrax in October 2001. Investigation of his workplace found traces of the bacterium in his work area and at least one other employee had been exposed to the bacterium. Letters carrying a highly effective powdered preparation of anthrax spores were sent to several politicians and journalists. The attack killed 5 people, most of whom were postal workers.
• Other cases of envelopes carrying anthrax occurring in Oct 2001 included letters posted to NBC and a subsidiary of Microsoft Corporation.

The History and Natural History of Anthrax.

Bacillus anthracis is a member of a very large genus of soil microorganisms. Most are harmless and unknown to the general public. Others are known, including B. thuringiensis, which is used as a natural insecticide. Some may know of B. subtilis, which is the source of the enzyme subtilisin that is used in laundry detergents. Only one other member of the genus, B. cereus, is at all well-known as a health hazard as it can cause an unpleasant form of gastroenteritis.

Soil microorganisms adapt well to poor growth conditions and the Bacilli have done this by forming spores, very hardy bodies that are inactive until conditions favor their growth. They are actually tough enough to survive dispersal by explosion and this method was tested by the British during World War II. The spores can survive for years in wool or animal hides and for decades or perhaps centuries in soil. One of the common names for anthrax - Woolsorter's disease - refers to the lethal pulmonary anthrax that can be contracted from handling wool from sheep that have been on contaminated soil. A layer of B. anthracis-containing soil can be buried if the land lies undisturbed only to be exposed to air and begin killing livestock if the soil is broken by the plough. Larry Wayne Harris obtained a pathogenic B. anthracis in the 1990's by exhuming cattle that had died of anthrax in the 1950's.

B. anthracis uses the combination of spores and lethality as a dispersal mechanism. When enough spores, or live cells, are taken up by an animal to cause it to develop anthrax and kill it. The bacterium particularly attacks the spleen, the German name for the disease is Milzbrand or inflamed spleen, but is found throughout the body. The area around the infected animal becomes contaminated as the animal begins to hemorrhage in the final stages of the disease. Carrion flies, birds and animals attack the corpse and take the disease with them and continue to disperse it. Louis Pasteur demonstrated that spores can pass through the digestive tract of earthworms. This would help spread the disease through the soil if the carcasses were simply buried. Although the disease does not readily pass directly between animals, this dispersal mechanism can contaminate large areas of land fairly rapidly. The treatment for diseased animals, especially in the wild, is no better than the disease. They are shot and the corpses burned where they lie.

Of the major diseases, anthrax is arguably the one with the longest confirmed history. It was described as a distinct disease by the ancient Greeks and anthrax is actually the Greek word for charcoal, referring to the deep black sores on the skin found in cutaneous anthrax, the commonest and most survivable form. It is thought that anthrax was the fifth or sixth plague of Egypt described in the book of Exodus.

Unlike most other old diseases seen as potential biological weapons, anthrax was not known for causing large-scale epidemics, but more for its economic effects. It is certainly poorly transmissible between people, but it can be contacted from contaminated surfaces and could easily wipe out flocks of sheep or herds of cattle, and still does today, and be economically devastating to an agrarian society. It was this that brought the minds of two of the great founders of bacteriology - Robert Koch and Louis Pasteur - to focus on the disease. Koch identified the bacterium in 1877 and it help him to formulate his postulates (Koch's postulates) that still guide microbiologists in identifying the agents causing diseases.

Pasteur's contributions to microbiology included the development of a vaccine that protected sheep from the disease, and therefore helped the economic recovery of some areas of France where the disease was common enough to hinder the rearing of livestock. They also included the development of the idea of attenuation - the development of weakened strains of an agent that can be used in vaccines to give protection without causing disease. He managed this by growing the bacterium at 42°C rather than 37°C. Safe and effective vaccines for humans are still not fully developed, underlining the scale of Pasteur's achievement.

Pasteur had achieved something that was so surprising that it took the better part of a century to explain it. The bacterial toxin is not coded for by genes of the bacterial chromosome, but by a plasmid. A plasmid is a small, independent piece of genetic material that does not use the same mechanisms as the host chromosome to maintain itself. This plasmid, known as pXO1, cannot maintain itself at 42°C so is lost from the cells, taking the disease-causing ability with it. There are now known to be two such virulence plasmids (pXO1 and pXO2) and modern diagnostic methods focus on rapid detection of these plasmids.

Anthrax has a long and ignoble history as a biological weapon. The first attempt to use it appears to have been a large-scale German plan to destroy Allied horse power using anthrax and glanders during World War I. Viable B. anthracis spores were recovered in 1997 from a glass ampoule inside a sugar cube that had been taken from a German officer in Norway in 1917.

The bacterium has been prepared for use as a weapon by the United Kingdom, the Soviet Union, and Iraq. The British prepared anthrax-impregnated cattle cake as a biological doomsday weapon for use against Germany in World War II. At the time, the United States prepared extensive facilities for the manufacture of B. anthracis (known as Agent N) on behalf of the British (Canada was involved to some extent) but demurred from developing it as an agent for itself.

In order to determine whether or not anthrax was a viable weapon, in the summer of 1942 British researchers went to Gruinard Island, off the coast of Scotland, and conducted a series of tests with anthrax-containing bombs. The tests were successful from the point of view of the weapons designers, demonstrating that the weapons could effectively disseminate the anthrax pseudospores; however, they left the island heavily contaminated. The cost of decontamination was originally thought to be too high, and the island was simply abandoned and placed off limits, its only sentinels warning signs.

The island became a bit of an embarrassment, however. Some authorities suggested that anthrax outbreaks in Scotland might be resulting from spores from the island, apart from which the simple fact that the testing had forced the abandonment of the island was continually embarrassing to the government (as when, as noted above in the section on terrorism, soil supposedly from Gruinard was used as a threat). Finally, in the 1980's, the British government undertook to decontaminate the island, conducting a survey to determine where the anthrax was and then studying means to decontaminate the soil.

After some experimentation, it was determined that a solution of formaldehyde 5% in seawater applied at a rate of 50 liters per square meter was effective in killing the anthrax spores without causing the soil to become infertile. During the summer of 1986, the areas on the island which had been found to be still contaminated were treated, samples were collected to see if spores had survived, and areas where viable spores were found were retreated until no anthrax was found. A flock of sheep was then settled on the island and watched. In 1990, when no anthrax had been seen, the British Ministry of Defense declared the island safe, returning it, in 1990, to the heirs of its original owners.

The Sverdlovsk Incident

The Sverdlovsk release was the subject of much controversy at the time. The American government felt it represented evidence of a major breach of the 1972 Convention on the Prohibition of Bacteriological and Toxin Weapons. An initial report on the outbreak by the Defense Intelligence Agency is now available in .pdf. The Soviet authorities said it had nothing to do with biological weapons and attributed the anthrax cases to tainted meat sold by "private butcher", with the animal infection arising from "a single 29-ton lot of bone meal (cattle feed) sold in March from a factory in Aramil, 15 kilometers to the southeast of Sverdlovsk." The Soviets also claimed all the deaths were due to intestinal anthrax. (Private butchers are common in the area and anthrax from improperly butchered meat is common in former Soviet Central Asia). Western intelligence sources had a different view, based on the distributions in space and time of human and animal cases.

The spatial distribution was very suggestive, as can be seen from this description:

There were also other indicators that the outbreak was not natural such as the presence of military decontamination teams on the streets and of police guards at the funerals of victims. But, in the end, the Soviet version of events would largely carry the day until 1992, when Boris Yeltsin, then President of Russia and in 1979 Communist Party chief in Sverdlovsk, acknowledged in a newspaper interview that the outbreak was caused by an accident at a biological warfare facility. Even after this admission, little information has been released, and the cause of the incident has not been stated, although Ken Alibek, in his 1999 book Biohazard states that it resulted from a failure to replace a clogged air filter.

In recent years, analysis on tissue samples from victims of the outbreak has demenstrated that the anthrax aerosol released from the facility was quite sophisticated, containing at least four separate strains of anthrax. In addition, the large distance it traveled (animal cases appeared some 50 kilometers downwind) suggests that it was well optimized for aerosol dissemination. The Soviets are also reported to have developed blends of B. anthracis strains intended to defeat known vaccines.

The inside of a 20,000 liter fermentor at a plant in Kazakhstan. The metal strips running up the fermentor wall are baffles that are a standard feature of fermentor design. The turbine, the fan-like object near the bottom of the tank appears to be a Rushden turbine.	The lower part of one of the four storey-high fermentors from the outside. The hall actually contained 10 of these.
Photographs: Center for Cooperative Threat Reduction

Iraq obtained anthrax for its biological weapons program, in part by buying it from the American Type Culture Collection. This points out one of the great problems in controlling biological weapons proliferation. Biological weapons organisms also constitute standing public health problems and are matters of legitimate research interest. There is a specific clause in the Biological and Toxin Weapons Convention that allows these organisms to be studied for genuine reasons of public good. Furthermore, anthrax is endemic in the Middle east and Iraqi scientists had already obtained at least one isolate of B. anthracis from a woman who had died of anthrax in the northern city of Mosul some years before they bought strains from the ATCC.

After the Gulf war, the Iraqis were noticeably evasive about their weaponization of anthrax, among other things claiming in 1995 in a "full and final accounting" to have filled 10 Scud missile warheads with weaponized anthrax and later, in 1997, in another "full and final accounting" to have filled only 5 missile warheads with anthrax. Subsequent questioning about this discrepency led some United Nations Special Commission personnel to the conclusion that the Iraqis had produced two different forms of anthrax for use in munitions - a wet slurry (easier to produce) and a dry form (better for dispersion) - and that they had actually filled 15 missile warheads with anthrax.

The threat of anthrax as a biological weapon led some to believe that it was necessary to vaccinate the US military against it. After a heated debate within the US national security establishment about the wisdom or necessity of the action, a vaccination program was begun in the late 1990's. The program was controversial as some believed that it was of limited effectiveness and because some believed it had played a role in the development of Gulf War Syndrome. In addition, Michigan Biologics had received a number of poor reviews of its performance from the US Food and Drug Administration. A small number of soldiers, sailors and airmen refused to take the vaccinations because of these concerns and were disciplined. The search for effective vaccines and protection against this and other agents continues.