Anthrax is a disease caused by a rod-shaped bacterium called Bacillus anthracis. The bacterium forms spores (tough dormant forms of the organism) that can live for decades in the soil. Robert Koch (1843– 1910), the German doctor who is considered the father of microbiology, identified the bacteria as the cause of anthrax in 1877.
Anthrax is primarily a disease of grazing animals such as sheep, goats, camels, and cattle. It rarely affects household pets like cats and dogs. It is one of the oldest animal diseases known to humans and is probably one of the ten plagues of Egypt described in the Book of Exodus in the Old Testament of the Bible. Animals can become infected by anthrax through
eating grass coated with anthrax spores or getting the spores into open wounds on their hides. Thousands of cattle in Europe and North America died each year from anthrax until French scientist Louis Pasteur (1822–1895) developed an effective vaccine against the bacteria in 1881.
Anthrax can take three different forms in humans. The most common form, accounting for 95 percent of cases, is cutaneous (skin-related) anthrax. It occurs when anthrax spores enter the body through a cut or break in the skin, producing a painless sore with a black center. Cutaneous anthrax is easily treated with antibiotics and is rarely fatal unless the infection spreads into the bloodstream.
The second form is gastrointestinal anthrax. Humans can get it by eating raw or undercooked meat from an infected animal. In this form of anthrax, the bacteria cause inflammation of the intestines leading to ulcers in the tissues lining the digestive tract. The infected person experiences nausea, vomiting, and bloody diarrhea. Between 25 and 60 percent of people with this form of anthrax die.
Inhalation anthrax is the third form, caused when anthrax spores enter a person's nose and throat and are carried to the lungs. The spores enter the lymphatic system and the lymph nodes in the central chest cavity. There, the spores germinate into active bacteria. The bacteria enter the bloodstream
and are carried throughout the body. The bacteria then produce toxins that cause bleeding, tissue destruction, and eventual death.
Inhalation anthrax is fatal in about 75 percent of cases even when treated. This form of anthrax used to be called woolsorter'sorrag-picker's disease because it was most likely to affect weavers and other people who worked with wool or hair taken from infected animals. Inhalation anthrax is the form most feared today because it is the form that develops when anthrax spores are used as a method of bioterrorism.
Anthrax is a relatively rare disease in humans in developed countries since the introduction of Pasteur's vaccine made it possible to protect animals from the disease. Other safety measures include the sterilization of animal waste materials.
Prior to the 2001 anthrax mailings, the last case of inhalation anthrax in the United States took place in 1976, when a weaver in California died after using wool imported from Pakistan. In 2006 an artist in the United Kingdom died from inhalation anthrax linked to working with untreated animal skins. The last known case of gastrointestinal anthrax in the United States occurred in 2000, when several people in Minnesota fell ill after eating meat from an infected steer.
2001 Anthrax Mailings
Within a week of the terrorist attacks of September 11, 2001 on the United States, letters containing spores of a particularly powerful strain of the anthrax bacteria were mailed to several news offices and two U.S. senators. An expert molecular biologist who examined the spores in the letters described them as “weapons grade.” Twenty-two people are known to have developed anthrax from the letters; half experienced the inhalation form of the disease. Five of the victims died: an editor at a Florida newspaper, a Vietnamese immigrant who worked in a New York hospital, an elderly widow in Connecticut, and two postal employees in Washington, D.C.
As of early fall 2008 the identity of the perpetrator is still uncertain. Suspicion was first directed toward a virologist named Steven Hatfill in 2003, then redirected toward a researcher at the Army medical research institute in Maryland named Bruce Ivins. Ivins killed himself at the end of July 2008 when he was informed that he was about to be prosecuted for the 2001 anthrax mailings. Although a team of scientists working since 2001 traced the anthrax samples in the letters to one specific flask of anthrax in Ivins's laboratory, some people think that someone other than Ivins may have had access to the flask and mailed the contaminated letters. The motive of the anthrax mailer as well as his or her identity may never be known.
People of all races and ages are equally likely to get inhalation anthrax when the bacillus is used as a weapon of bioterrorism. Cutaneous and gastrointestinal anthrax are rare in the United States. Young adults are the age group most commonly affected due to occupational exposure. People in the following occupations are at some risk of cutaneous anthrax:
- Farmers and ranchers
- Forest rangers, field biologists, and others who study wildlife
- People who work with wool, animal hides, hair, or bone meal products
The cause of anthrax is a bacterium, B. anthracis. The bacteria cause organ destruction and internal bleeding in animals and humans through the release of toxins that target the tissues lining blood vessels, lymph vessels, and the intestines. One of the toxins causes fluid to build up in the tissues and damages the body's immune system, while the other toxin kills infected cells directly.
It is important to understand that humans cannot transmit anthrax directly to one another, although a person's skin, hair, or clothing can be contaminated by anthrax spores. People can be decontaminated after exposure to anthrax spores by showering in hot water and using an antimicrobial soap. Suspected articles of clothing should be boiled in water for a minimum of thirty minutes or else burned. It is not necessary to isolate or quarantine a living patient diagnosed with anthrax after he or she has been decontaminated.
The symptoms of anthrax depend on the type:
- Cutaneous: The incubation period is between two and five days after the spores get into a cut or break in the skin. An itchy papule (raised skin lesion) appears, followed by a blackish painless ulcer about an inch across with a round, swollen edge. Nearby lymph nodes may be swollen. The ulcer lasts for about two weeks before separating from the skin and leaving a permanent scar. The infection spreads into the bloodstream in about 5 to 10 percent of untreated patients.
- Gastrointestinal: Symptoms appear between two and five days after eating infected meat. The patient experiences nausea, vomiting, painful abdominal cramps, loss of appetite, vomiting blood, and bloody diarrhea.
- Inhalation: The symptoms begin abruptly, usually within one to three days after exposure. However, in some cases it may take as long as forty-two days after exposure (and perhaps longer) for the person to feel sick. The person first notices coughing and mild discomfort around the breastbone, quickly followed by high fever, severe shortness of breath, coughing or vomiting blood, heavy sweating, and chest pain severe enough to be mistaken for a heart attack.
There is no screening test for anthrax. Diagnostic tests for the various forms of anthrax are ordered according to the patient's history— including his or her occupational history—and specific symptoms:
- Skin scraping or biopsy: A sample of tissue fluid from the characteristic skin ulcer caused by cutaneous anthrax can be stained and viewed under a microscope for evidence of the anthrax bacteria.
- Sputum culture. The secretions from the lungs of a patient with inhalation anthrax can also be examined under a microscope.
- Stool sample. Stool can be tested for anthrax bacteria in cases of suspected gastrointestinal anthrax.
- Endoscopy. An endoscope is a lighted flexible tube that can be inserted into the throat or the intestines to look for the characteristic ulcers caused by the anthrax bacteria.
- Chest x ray or computed tomography (CT) scan. These imaging studies can be done to look for signs of inhalation anthrax.
- Blood test and laboratory culture. This test can be done to check for any of the three forms of anthrax. The sample is cultured on a material called blood agar, which is made from animal blood combined with a gelatin-like substance derived from seaweed. If B. anthracis is present, the red blood cells in the gelatin surrounding the bacterial colony will be destroyed.
All three forms of anthrax are treated with oral or intravenous antibiotics. Penicillin is usually effective for cutaneous anthrax. However, ciprofloxacin and doxycycline are usually recommended for the other forms of the disease. Inhalation anthrax requires hospitalization and treatment with intravenous antibiotics. People who may have been exposed to anthrax may be given antibiotics for as long as sixty days to prevent inhalation anthrax.
Cutaneous anthrax has the best prognosis; most people recover without complications except for a scar where the ulcer appeared. Gastrointestinal anthrax has a mortality rate of 25 to 60 percent, while inhalation anthrax has a death rate between 45 and 75 percent even when treated.
Anthrax can be prevented in several ways. One preventive measure is to give a sixty-day course of antibiotics to anyone exposed to the disease. Another preventive measure is to avoid eating raw or under-cooked meat.
There is a vaccine against anthrax that was approved by the Food and Drug Administration (FDA) in 1970, but it is not given to the general public. Those who are eligible to receive the vaccine include:
- Active-duty military personnel in areas that carry a high risk of exposure to anthrax.
- Researchers and laboratory assistants who work with anthrax.
- People who must work with animal products in parts of the world where livestock are not routinely vaccinated against anthrax.
- People who work with animal hides or wool imported from these countries.
People or animals who die from anthrax must be buried or otherwise disposed of carefully in order to prevent contaminating others. The body of a person who is known to have died from anthrax is considered a bio-hazard because the skin and any body fluids can contaminate healthcare workers. The body must be placed in an airtight bag and preferably cremated, as burial will not kill anthrax spores.
Anthrax is a major concern to public health officials because of its potential as an agent of bioterrorism. The Centers for Disease Control and Prevention (CDC) classifies anthrax as a Category A agent, the highest of three levels. Category A agents are defined as disease organisms that pose the greatest possible threat to public health; can be easily spread over a large geographic area; and require a high level of planning in order to protect the public. In addition, the fact that anthrax spores can survive in the environment for years makes the disease even more dangerous. In 1942, during World War II, the British deliberately tested anthrax as a bioweapon on a small island off the coast of Scotland. It took until 1990 for the island to be completely decontaminated.
SEE ALSO Ebola and Marburg hemorrhagic fevers; Plague; Smallpox
WORDS TO KNOW
Bioterrorism: The use of disease agents to frighten or attack civilians.
Cutaneous: Pertaining to the skin.
Papule: A small cone-shaped pimple or elevation of the skin.
Quarantine: The practice of isolating people with a contagious disease for a period of time to prevent the spread of the disease.
Spore: A dormant form of the anthrax bacteria that can live for decades before being reactivated and reproducing.
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