BBC News Online looks at anthrax and how the potentially deadly disease can be used as a weapon.
Cleaning up after an anthrax scare in the US
What is it?: A disease caused by the organism bacillus anthracis (see image A).
Effects and symptoms: Anthrax is not contagious from person to person, and can only develop if the bacteria gets into a cut or if enough anthrax spores are inhaled, or infected meat is eaten.
There are three main types of the disease, named to refer to the way the infection attacks the body - cutaneous (via the skin), gastro-intestinal (stomach), and pulmonary or inhalation (lungs). The incubation period is usually between one and six days - although it can be up to 60 days for inhalation anthrax.
The symptoms for cutaneous anthrax include itchy boils which turn into black-coloured open sores. This form of the disease is rarely fatal and can be treated with antibiotics.
Gastro-intestinal anthrax can kill well over a quarter of those who contract it. The symptoms are fever, abdominal pain, vomiting blood and acute diarrhoea.
Inhalation anthrax is the most dangerous. An initial phase of flu-like symptoms can usually last for one to three days, before the patient enters a second phase of high fever, chest pains, severe breathing problems and shock. Death usually follows within two days.
Use as a weapon: It is possible to use anthrax as a military weapon by placing it in missiles, rockets or bombs. Anthrax spores could also be released by planes which could spray it over large areas. Once present the spores can remain dormant for decades.
The wave of anthrax attacks that occurred in the US in late 2001 also showed that attackers could use the bacteria by simply placing the spores in envelopes. Such methods are unlikely to cause many casualties but create disruption and a climate of fear.
History: Anthrax is rare in humans but animals often get the disease in large parts of Asia, South America and Africa.
The British experimented with anthrax as a weapon in the 1940s and the US made some for military use in the 1950s and 1960s. The Soviet Union also weaponised anthrax and Iraq admitted to doing so in 1995. Five people in the US died from inhalation anthrax during the 2001 attacks. It is still not known who was behind the attacks.
Production: The anthrax bacterium is easy to cultivate for those with some scientific knowledge. However, the Aum Shinrikyo cult in Japan tried and failed to produce anthrax.
Protection: A vaccination is available, but as with most vaccines, it is not a 100% effective. Over half a million American soldiers have been vaccinated, with acute reaction experienced by about one person in a 100,000. Inhalation of anthrax spores can be prevented with mouth and nose respiratory protection.
Treatment for anthrax: High dose antibiotics are used, but victims showing advanced symptoms of the disease may not respond. Some strains of anthrax can naturally resist penicillin.