Anthrax is an infection caused by the bacterium Bacillus anthracis. Its name comes from the black spots that can appear on the body in the cutaneous (skin) form of the disease; to suggest the color of the spots, doctors used the Greek word for coal, “anthrax.” Anthrax is usually transmitted through hardy spores that can survive in soil for decades. Anthrax exists naturally in many parts of the world as an infection of herbivores (plant-eating animals), such as cattle and sheep. Because its spores are small enough to become airborne, anthrax can be contracted by humans as a lung infection. In this form it is fatal in at least 95% of cases that do not receive immediate antibiotic treatment. Because of the high fatality rate of the inhaled form of the disease, anthrax has been developed as a biological weapon by several major nations, including Japan, Russia, the United Kingdom, and the United States. No nation is known today to retain stocks of weaponized anthrax, but there is concern that terrorists might use anthrax as a weapon.
Disease History, Characteristics, and Transmission
Anthrax is a naturally occurring disease afflicting live-stock and occasionally, through contact with livestock, Page 42 | Top of Articlehumans. Records show that in Europe in the 1600s, a cattle disease that was almost certainly anthrax, called the Black Bane, killed about 60,000 cattle. Until the development of antibiotics and an effective veterinary vaccine for anthrax in the mid-twentieth century, anthrax was one of the most common causes of death for cattle, goats, horses, pigs, and sheep.
In 1876, the German physician Robert Koch (1843–1910) showed that a bacterium was responsible for the disease, making anthrax one of the first diseases to be identified as having a bacterial cause. Koch, who was awarded a Nobel Prize in Medicine in 1905, also discovered the bacterial causes of tuberculosis and cholera. Cattle were first successfully in oculated against anthrax in 1880 by the French biologist Louis Pasteur (1822–1895).
The use of anthrax in modern warfare began in 1915 during World War I, when a German-American agent working for the Imperial German Government set up a secret laboratory in Washington, D.C., to produce anthrax bacteria. These were then used to infect cattle and draft animals being shipped to the Allied armies in Europe. Several hundred Allied military personnel were infected by the anthrax-ridden cattle.
During World War II (1939–1945), anthrax was developed as a major weapon by several countries. A biological warfare unit, Unit 731, was formed in the Japanese Imperial Army, which carried out experiments on thousands of Chinese prisoners of war in the 1930s. In one facility, about 4,000 prisoners were killed by biological agents, mostly anthrax. By 1945, Japan had prepared about 880 lb (400 kg) of powdered anthrax spores for use in fragmentation bombs intended to spread the spores in the air to be inhaled. Japan Page 43 | Top of Articlesurrendered before using anthrax bombs, but historians estimate that Japan may have killed over a half a million Chinese civilians using other forms of biological warfare. All members of Unit 731 were granted amnesty by the United States after the war in exchange for full disclosure of their wartime activities.
Japan was not the only country to place anthrax in bombs during World War II. In the United States, a major of fensive bio war program was established at the Army's Camp Detrick, Maryland, in 1942. Anthrax and a number of other agents were developed as weapons there, and a plant for producing biological weapons was constructed near Terre Haute, Indiana. Thousands of anthrax bombs were produced, but none were used during the war. The British government, which was cooperating with the United States and Canada in developing anthrax as a weapon, contaminated the Scottish island of Gruinard with anthrax spores in 1942. Due to the long-lived nature of the spores, the island was off-limits for 48 years afterward, when it was finally decontaminated. The difficulty of decontaminating Gruinard shows how a large-scale attack with anthrax spores might render large areas of land uninhabitable. Decontamination of the small island involved soaking it in 308 tons (280 metric tons) of formaldehyde diluted in seawater and the removal of tons of topsoil in sealed containers.
Anthrax bacteria in their vegetative form are shaped like rods about 1 millionth of a meter (1 μm) wide and 6 μm long. The vegetative form multiplies inside a host animal. When conditions are not right for anthrax to grow and multiply—namely, when temperature, acidity, humidity, and nutrient levels are outside the favorable range—some of the vegetative anthrax bacteria sporulate, that is, take on a spore form. A spore is an extremely small, one-celled reproductive unit that is usually able to survive extreme environmental conditions. Unlike a seed, a spore does not store a significant amount of nutrients. Anthrax spores can survive in soil or as a dry powder for many years and are the most common source of anthrax infection.
Once in the body, anthrax spores germinate and multiply. Toxins released by the bacteria cause the immune system to break down. In the final phase of infection, the bacteria build rapidly in the blood, doubling in number every 0.75–2 hours. At death, there may be more than 108 (100,000,000) anthrax bacteria per milliliter of blood. (A milliliter is about the size of a small drop.) Toxins from the bacteria break down the blood vessels, causing death by internal bleeding.
After death, the bacteria continue to multiply in the carcass. Large numbers of spores are shed to the surrounding soil. The anthrax life cycle is continued when other creatures either eat the flesh of the dead animal or ingest enough of the spores.
There are three basic types of anthrax infection: pulmonary, cutaneous, and gastrointestinal (also called enteric, meaning of the intestines) anthrax. Pulmonary or lung infection with anthrax is caused by inhalation of spores; cutaneous or skin infection is caused by entry of spores or bacteria into cuts or sores; and gastrointestinal infection is caused by eating anthrax-contaminated meat.
Anthrax is usually contracted either by taking spores or bacteria into the body through a lesion (cut or open sore), through the bite of a fly, by eating the flesh of an anthrax-infected animal, or by inhaling spores. Direct transmission of anthrax between humans is extremely rare.
Humans are moderately resistant to anthrax. The infectious dose for inhalation anthrax, measured by spore count, is probably between 2,500 and 760,000 spores, the range recorded for non-human primates. The U.S. Department of Defense estimates that 8,000–10,000 spores is the anthrax LD50 for humans; LD50 stands for “lethal dose 50,” the amount of an agent that will be fatal in about 50% of cases. Scientists have shown that in contaminated industrial settings, people can inhale over 1,000 anthrax spores per day without contracting the disease. When anthrax is developed as a weapon, it is meant to be delivered in extremely large quantities. For example, 220 lb (100 kg) of spores, often cited as a working figure in discussions of possible large-scale military use, contain about 1013 (10,000,000,000,000 or ten trillion) LD50 doses—about 1,500 times the population of the world. However, most of the spores distributed by a weapon would not end up being inhaled.
Scope and Distribution
As a naturally occurring disease, anthrax mostly afflicts cattle. In humans, it is relatively rare. Persons in agricultural settings in poor nations, who are likelier to contract the disease from livestock, account for the great majority of human anthrax cases worldwide. Natural anthrax remains hyperendemic or epidemic in about 14 countries today, including Burma (also known as Myanmar), Chad, Niger, Turkey, and Zambia. It is endemic in China, India, Indonesia, much of Latin America and Africa, and sporadic in most of the rest of the world, including Australia, the United States, and Europe. (A sporadic disease occurs only occasionally; an endemic disease coexists normally with its host population; a hyperendemic disease co-exists with its host population at a high rate; and an epidemic disease is one that episodically occurs at a high rate.) Human case rates are highest today in central and southern Asia, the Middle East, and Africa.
The human anthrax rate normally depends on the livestock anthrax rate in a given area. There is about one human cutaneous anthrax case for every 10 anthrax-infected livestock carcasses processed and one enteric case for every 100–200 cutaneous cases. Inhalation anthrax is relatively rare.
Treatment and Prevention
Prevention of anthrax is based on breaking the cycle of infection, which primarily means controlling its appearance in livestock. The World Health Organization (WHO) of the United Nations is trying to set up a global network of anthrax experts and diagnostic laboratories to better monitor and respond to anthrax outbreaks worldwide. WHO says that the following steps must be rigorously implemented when dealing with anthrax-infected livestock:
- Correct disposal of carcasses of animals with anthrax. This means deep burial, heat treatment, or incineration without a post-mortem (to avoid releasing spores).
- Page 46 | Top of Article Disinfection and disposal of all contaminated materials. This includes the processing of possibly infected animal hides before export, the incineration or burial of dung, the chemical sterilization of tools, and the thorough washing of hands.
- Vaccination of susceptible animals and humans in at-risk occupations, such as those processing meat, hides, and wool.
Vaccination is not universal for livestock because of its expense. It is not universal for humans because of the expense and the risk of presently available anthrax vaccines. The only anthrax vaccine that is approved by the government for use in the United States—trade name Biothrax, first licensed in 1970—involves giving the subject six injections over 18 months. This vaccine is mandatory for some categories of U.S. military personnel and civilian defense contractors. However, because the potency of the vaccine varies greatly, some scientists argue that many military personnel have suffered health damage from the vaccine.
For persons in contact with human anthrax patients, prophylactic (preventative) antibiotics are given. Treatment of anthrax infection is with large doses of anti-biotics, both swallowed (oral) and injected directly into the bloodstream (intravenous). Especially for inhalation anthrax, treatment must begin soon after infection— generally within a day and before symptoms are seen.
Impacts and Issues
In countries where anthrax is naturally present, it exacts a steady human and economic toll. Persons contracting the disease may die or live with a decreased quality of life. Animals that contract the disease must be destroyed, and their carcasses are economically worthless.
The mere threat of the use of anthrax as a weapon has caused the U.S. government to undertake extraordinary preventive efforts in addition to its military vaccination program. In 2004, as part of a $5.6 billion program called Project BioShield, intended to protect the public from biological threats, the federal government ordered 75 million doses ($877 million worth) of a new anthrax vaccine from a private company, VaxGen Inc., to be stockpiled in case of an anthrax attack on the United States. The new vaccine was to have required no more than three separate injections. The U.S. Department of Health and Human Services (HHS) has also stockpiled over a billion antibiotic tablets, enough to treat 20 million people for two months. The new anthrax vaccine was to be delivered in 2006, but the program was delayed. In December 2006, HHS cancelled its contract with VaxGen because the company was not able to start human clinical trials of its new vaccine on time. This leaves Project Bioshield without a plan for producing an emergency stock of anthrax vaccine for public use.
Sarasin, Philipp, and Giselle Weiss. Anthrax: Bioterror as Fact and Fantasy. Cambridge, MA: Harvard University Press, 2006.
Broad, William J. “Anthrax Not Weapons Grade, Official Says.” New York Times (September 26, 2006).
Enserink, Martin, and Jocelyn Kaiser. “Accidental Anthrax Shipment Spurs Debate Over Safety.” Nature 304 (2004): 1726–1727.
Hilts, Philip J. “79 Anthrax Traced to Soviet Military.” New York Times (November 18, 1994).
Lipton, Eric. “Bid to Stockpile Bioterror Drugs Stymied by Setbacks.” New York Times (September 18, 2006).
Rosovitz, M.J., and Stephen H. Leppla. “Virus Deals Anthrax a Killer Blow.” Nature 418 (2002): 825–826.
British Broadcasting Corporation. “Britain's ‘Anthrax Island.”’ July 25, 2001. <http://news.bbc.co.uk/2/low/uk_news/scotland/1457035.stm > (accessed January 30, 2007).
World Health Organization. “Guidelines for the Surveillance and Control of Anthrax in Humans and Animals.” <http://www.who.int/csr/resources/publications/anthrax/WHO_EMC_ZDI_98_6/en /> (accessed January 30, 2007).
World Health Organization. “World Anthrax Data Site.” September 30, 2003. <http://www.vetmed.lsu.edu/whocc/mp_world.htm > (accessed January 30, 2007).