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Anthrax

Definition, Description, Causes and symptoms, Diagnosis, Treatment, Prognosis, Prevention

Anthrax is a bacterial infection caused by Bacillus anthracis that primarily affects livestock but that can occasionally spread to humans, affecting either the skin, intestines, or lungs. In humans, the infection can often be treated, but it is almost always fatal in animals.

Description

Anthrax is most often found in the agricultural areas of South and Central America, southern and eastern Europe, Asia, Africa, the Caribbean, and the Middle East. In the United States, anthrax is rarely reported, however, cases of animal infection with anthrax are most often reported in Texas, Louisiana, Mississippi, Oklahoma, and South Dakota. The bacterium and its associated disease get their name from the Greek word meaning "coal" because of the characteristic coal-black sore that is the hallmark of the most common form of the disease.

During the 1800s, in England and Germany, anthrax was known either as "wool-sorter's" or "ragpicker's" disease because workers contracted the disease from bacterial spores present on hides and in wool or fabric fibers. Spores are the small, thick-walled dormant stage of some bacteria that enable them to survive for long periods of time under adverse conditions. The first anthrax vaccine was perfected in 1881 by Louis Pasteur.

Humans suffering from anthrax often develop ulcerating nodules on the body. Custom Medical Stock Photo. Reproduced by permission.) Humans suffering from anthrax often develop ulcerating nodules on the body. Custom Medical Stock Photo. Reproduced by permission.)

The largest outbreak ever recorded in the United States occurred in 1957 when nine employees of a goat hair processing plant became ill after handling a contaminated shipment from Pakistan. Four of the five patients with the pulmonary form of the disease died. Other cases appeared in the 1970s when contaminated goatskin drumheads from Haiti were brought into this country as souvenirs. Today, anthrax is rare, even among cattle, largely because of widespread animal vaccination. However, some serious epidemics continue to occur among animal herds and in human settlements in developing countries due to ineffective control programs.

There has been a great deal of recent concern that the bacteria that causes anthrax may be used by some countries as a type of biological warfare, since it is possible to become infected simply by breathing in the spores. The largest-ever documented outbreak of human anthrax contracted through spore inhalation occurred in Russia in 1979, when anthrax spores were released from a military laboratory, causing a regional epidemic that killed 69 of its 77 victims. Because the United States government considers anthrax to be of potential risk to soldiers, the Department of Defense has begun systematic vaccination of all military personnel against anthrax, and other nations, such as Britain, are rapidly following suit.

Causes and symptoms

Anthrax is caused by the bacterium Bacillus anthracis, which produces spores that can remain dormant for years in soil and on animal products, such as hides, wool, hair, or bones. The disease is often fatal to cattle, sheep, and goats, and their hides, wool, and bones are often heavily contaminated.

Today, in humans, the disease is almost always an occupational hazard, contracted by those who handle animal hides (farmers, butchers, and veterinarians) or sort wool. It is also possible to become infected with anthrax by eating meat from contaminated animals. There are no reports of the disease spreading from one person to another.

Symptoms vary depending on how the disease was contracted, but the symptoms usually appear within one week of exposure.

Cutaneous anthrax

In humans, anthrax usually occurs when the bacteria enter a cut or abrasion, causing a skin (cutaneous) infection at the site. Cutaneous anthrax, as this infection is called, is the mildest form of the disease. At first, the bacteria cause an itchy, raised area like an insect bite. Within one to two days, inflammation occurs around the raised area, and a blister forms around an area of dying tissue that becomes black in the center. Other symptoms may include shivering and chills. In most cases the bacteria remain within the sore. If, however, they spread to the nearest lymph node (or, in rare cases, escape into the bloodstream), the bacteria can cause a form of blood poisoning that rapidly proves fatal.

Inhalation anthrax

Inhaling the bacteria or bacterial spores can lead to a rare, fatal form of anthrax known as pulmonary or inhalation anthrax that attacks the lungs and sometimes spreads to the brain. Inhalation anthrax begins with flulike symptoms, namely fever, fatigue, headache, and shortness of breath, but progresses to bronchitis, during which time it becomes difficult to breathe, and finally, the patient enters a state of shock. This rare form of anthrax is usually fatal, even if treated within one or two days after the symptoms appear.

Intestinal anthrax

Intestinal anthrax is a rare, often-fatal form of the disease, caused by eating meat from an animal that died of anthrax. Intestinal anthrax causes stomach and intestinal inflammation and sores or lesions (ulcers), much like the sores that appear on the skin in the cutaneous form of anthrax. The first signs of the disease are nausea and vomiting, loss of appetite, and fever, followed by abdominal pain, vomiting of blood, and severe bloody diarrhea.

Diagnosis

Anthrax is diagnosed by detecting B. anthracis in samples taken from blood, skin lesions, or respiratory secretions. The bacteria may be positively identified using biochemical methods or using a technique whereby, if present in the sample, the anthrax bacterium is made to fluoresce. Blood samples will also indicate elevated antibody levels or increased amounts of a protein produced directly in response to infection with the anthrax bacterium. Additional DNA-based tests are also currently being perfected.

Treatment

In the early stages, anthrax is curable by administering high doses of penicillin, but in the advanced stages, it can be fatal. Other commonly used antibiotics, such as erythromycin, tetracycline, or chloramphenicol, are also effective, particularly for those individuals who are allergic to penicillin. Although not proven, it is thought that newer antibiotics, like ciprofloxacin and some cephalosporins, may also prove effective. Although cutaneous anthrax may be cured following a single dose of antibiotic, it is important to continue treatment so as to avoid potential serious complications, such as inflammation of the membranes covering the brain and spinal cord (meningitis).

Prognosis

Untreated anthrax is often fatal, but death is far less likely with appropriate care. Ten to twenty percent of patients will die from anthrax of the skin (cutaneous anthrax) if it is not properly treated. All patients with inhalation (pulmonary) anthrax will die if untreated. Intestinal anthrax is fatal 25-75% of the time.

Prevention

Anthrax is relatively rare in the United States because of widespread animal vaccination and practices used to disinfect hides or other animal products. For those in high-risk professions, an anthrax vaccine is available that is 93% effective in protecting against infection. To provide this immunity, an individual must be given an initial course of three injections, given two weeks apart, followed by booster injections at 6, 12, and 18 months and an annual immunization thereafter.

Approximately 30% of those who have been vaccinated against anthrax may notice mild local reactions, such as a slight tenderness at the injection site. Someone who has already had anthrax might have a more severe local reaction upon vaccination. Infrequently, there may be a severe local reaction with extensive swelling of the forearm, and only a very few vaccine recipients may have a more general flu-like reaction to the shot.

Other means of preventing the spread of infection include carefully handling dead animals suspected of having the disease and providing good ventilation when processing hides, fur, wool, or hair. Whether this vaccine would protect against anthrax used as a biological weapon is, as yet, unclear.

Anyone visiting a country where anthrax is common or where herd animals are not often vaccinated should avoid contact with livestock or animal products and avoid eating meat that has not been properly prepared and cooked.

Resources

BOOKS

Infectious Disease. Ed. Barbara A. Bannister, et al. Oxford, England: Blackwell Scientific, Inc., 1996.

Van De Graaff, Kent. Survey of Infectious and Parasitic Diseases. New York: McGraw Hill, 1996.

Wilks, David, et. al. The Infectious Diseases Manual. Oxford, England: Blackwell Scientific, Inc., 1995.

ORGANIZATIONS

Centers for Disease Control and Prevention. 1600 Clifton Rd., NE, Atlanta, GA 30333. (800) 311-3435, (404) 639-3311. <http://www.cdc.gov>.

National Institute of Allergies and Infectious Diseases, Division of Microbiology and Infectious Diseases. Building 31, Room. 7A-50, 31 Center Drive MSC 2520, Bethesda, MD 20892. <http://www.niaid.nih.gov>.

World Health Organization, Division of Emerging and Other Communicable Diseases Surveillance and Control. Avenue Appia 20, 1211 Geneva 27, Switzerland. (+00 4122) 791 21 11. <http://www.who.int>.

OTHER

"Anthrax." New York State Department of Health communicable Disease Fact Sheet. <http://www.health.state.ny.us/nysdoh/consumer/anthrax.htm>.

"Anthrax: Memo From a WHO Meeting." World Health Organization. Bulletin of the World Health Organization, 74(5)(Sept.-Oct. 1996):456-61.

"Bacterial Diseases." Healthtouch Online Page. <http://www.healthtouch.com>.

"Bacillus anthracis (Anthrax)." <http://web.bu.edu/COHIS/infxns/bacteria/anthrax.htm>.

Centers for Disease Control. <http://www.cdc.gov/nccdphp/ddt/ddthome.htm>.

Carol A. Turkington

KEY TERMS


Antibody—A specific protein produced by the immune system in response to a specific foreign protein or particle called an antigen.

Bronchitis—Inflammation of the mucous membrane of the bronchial tubes of the lung that can make it difficult to breathe.

Cutaneous—Pertaining to the skin

Meningitis—Inflammation of the membranes covering the brain and spinal cord called the meninges.

Pulmonary—Having to do with the lungs or respiratory system.

Spore—A dormant form assumed by some bacteria, such as anthrax, that enable the bacterium to survive high temperatures, dryness, and lack of nourishment for long periods of time. Under proper conditions, the spore may revert to the actively multiplying form of the bacteria.

Additional topics

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