Anthrax is a potentially fatal disease caused by the bacterium Bacillus anthracis. These bacteria produce spores that can spread the infection. Spores are bacteria in a resting stage. Like plant seeds, they are not active until they germinate.
Anthrax in humans is rare unless the spores are spread intentionally. Anthrax usually develops in cattle, horses, sheep, and goats. Historically, anthrax infections in North America occurred in people who worked with animals, such as veterinarians or ranchers. But anthrax is now extremely rare in animals in North America because of vaccination and other control efforts.
In 2001, the general population became concerned after 22 cases of anthrax occurred in the United States as a result of bioterrorism. Most of those cases involved U.S. postal workers and media employees who were exposed to anthrax spores when handling mail.
Humans can develop four types of anthrax infection:
Of the four types, inhalational anthrax is the most likely to cause death. Cutaneous anthrax is the most common form, while gastrointestinal and oropharyngeal anthrax are the least common.
Anthrax is caused by the bacterium Bacillus anthracis. The only way you can develop anthrax is by direct exposure to the bacterial spores through the skin, by eating contaminated food, or by inhaling airborne spores from the environment. People who come in contact with those who have the disease do not need to be immunized or treated unless they were exposed to the same source of infection.
Not everyone who has been exposed to anthrax will develop infection. But doctors will treat you to prevent infection if you have been exposed to anthrax spores.
Although anthrax is very rare in Canada, certain jobs, activities, and hobbies can increase the risk of getting an anthrax infection.
The incubation period—the time from exposure to anthrax until symptoms develop—depends on how the anthrax is spread. In general, the symptoms depend on the type of infection.
Your doctor will use a medical history and tests to find out whether you have been exposed to anthrax spores. The doctor will ask where you work and about other environmental exposures that may put you at risk. It is likely that you will be notified by a public health official of a possible exposure to anthrax spores.
Anthrax is confirmed when the bacteria are identified from a culture and sensitivity test of your blood, spinal fluid, skin sores, or respiratory secretions.
You may have other tests to look for anthrax. A biopsy of a skin ulcer may be done to diagnose cutaneous anthrax. If your doctor suspects you have inhalational anthrax, you probably will have imaging tests—a chest X-ray or a computed tomography (CT) scan—to look for changes to your chest or lymph nodes.
All types of anthrax exposure can be treated effectively with antibiotics such as ciprofloxacin, doxycycline, or penicillin. Prompt treatment may reduce the severity of the infection.
To be effective against inhalational and gastrointestinal anthrax, antibiotics must be given immediately after a known or suspected exposure. These types of anthrax do not respond well to antibiotics after symptoms develop.
You may receive supportive treatment in the hospital to help your body fight the infection. These measures include giving oxygen, fluids, and corticosteroids.
Medicine can prevent infection before and soon after exposure to anthrax spores.
If you are at risk of exposure to anthrax, you will be vaccinated. The anthrax vaccine, given in a series of five shots over 18 months, plus annual boosters, has potential side effects. These include fever, headache, joint pain, and fatigue.
If you are exposed to anthrax, you will receive antibiotics and a few doses of the vaccine.
Usually, people known or believed to have been exposed to inhalational anthrax receive either ciprofloxacin or doxycycline for 60 days to prevent infection. In some cases, other antibiotics may be used.
Currently, the vaccine is not recommended for or available to the public. In Canada, the vaccine has been used only for people at high risk of exposure, such as members of the Canadian Forces.
Learning about anthrax:
If you think you have been exposed to anthrax spores, call your local law enforcement agency and your doctor immediately or contact your local health unit. See your local government pages in the phone book. Because anthrax cannot be spread from person to person, the people around you are not at risk unless they also have been exposed to anthrax spores.
Cutaneous anthrax usually occurs when spores from the bacteria enter a cut or scrape on the skin. Cutaneous anthrax infection has the following characteristics:
Other symptoms may include:
This form of anthrax occurs after eating meat contaminated with the bacteria that cause anthrax. Gastrointestinal anthrax can be more serious than cutaneous anthrax but can be treated effectively with prompt use of antibiotics. But if untreated, gastrointestinal anthrax causes:
These symptoms are followed by:
Within 2 to 4 days after these symptoms develop, fluid (ascites) fills the abdomen; shock and death usually follow within 2 to 5 days.
The most lethal form of exposure occurs from inhalational anthrax. The incubation period for this form of anthrax may be 60 days or more, although it is usually 2 to 3 days. Initial symptoms can include:
Symptoms can progress rapidly after just a few days to include:
Death can occur within 24 to 36 hours after such complications occur. Respiratory symptoms may be similar to those of pneumonia.
After the disease becomes severe, it is difficult to treat, and survival is unlikely. Inhalational anthrax is not contagious. You must inhale the spores from the environment to develop this form of anthrax. Even with the outbreaks in the United States in 2001, this type of exposure is still very rare.
The symptoms of inhalational anthrax infection may resemble those of influenza (flu), except for these key differences:4
This is the least common form of anthrax. The incubation period is from 1 to 7 days. Initial symptoms include:
As infection progresses, swelling can make breathing difficult.
If you have symptoms that could be caused by anthrax, your doctor will use a medical history and tests to find out whether you may have been exposed to anthrax spores. He or she will ask where you work and about other environmental exposures that may have put you at risk. Postal workers in the United States, for example, were at risk of exposure to spores in the 2001 bioterrorism attacks.
If your doctor is at all suspicious that you may have been exposed to anthrax, you will be treated with antibiotics until a diagnosis can be confirmed or ruled out.
Doctors diagnose anthrax when Bacillus anthracis bacteria are identified from a culture and sensitivity test of the blood, spinal fluid, skin sores, or respiratory fluids. The Anthrax Quick ELISA test may be used to identify the Bacillus anthracis bacteria. This test of the blood can be completed faster than previous tests for anthrax. Most doctors will not have the Anthrax Quick ELISA test in their office and will send blood samples to a laboratory to be tested.
Biopsy of a skin ulcer also may be done to diagnose cutaneous anthrax.
If results of a culture are not clear, blood tests or polymerase chain reaction (PCR) may be done.
Nose swabs may help provincial ministries of health determine how many people in an area have been recently exposed to anthrax. But they are not used to diagnose anthrax or to assist a doctor in deciding how to treat it.
You may have imaging tests to look for signs of inhalational anthrax infection.
Antibiotics are used to treat all types of anthrax infection. But early treatment after exposure is essential for inhalational and gastrointestinal anthrax. After severe infection is under way, treatment is usually not effective.
Anthrax generally can be destroyed with antibiotics, mainly ciprofloxacin, doxycycline, and penicillins. These antibiotics are taken for about 60 days.
Experts recommend two or more antibiotics to treat inhalational anthrax because this is the most lethal type.
The following are recommendations for the treatment of cutaneous and inhalational anthrax infection:5
Adults (including pregnant women) and children: Ciprofloxacin, doxycycline, or levofloxacin by mouth.
Adults (including pregnant women) and children: Ciprofloxacin or doxycycline and one or two additional antibiotics. Initial treatment is by vein (intravenous, or IV), followed by medicine by mouth. The dosage of these medicines is reduced in children.
Treatment for inhalational anthrax often is ineffective if the infection is under way. Supportive care in a hospital is essential. This care may include corticosteroids if fluid buildup (edema), respiratory trouble, or meningitis develops. Tubes may be used to drain fluid in the chest.
Currently, the vaccine is not recommended for or available to the public. In Canada, the vaccine has been used only for people at high risk of exposure, such as members of the Canadian Forces. Pregnant women should be vaccinated only if absolutely necessary.
The vaccine has potential side effects, including fever, headache, joint pain, and fatigue.
Antibiotic treatment usually can keep symptoms from developing. Just because you have been exposed to anthrax spores does not mean you will develop an infection. If antibiotics are given quickly, the spores may not have a chance to germinate and cause infection.
Taking antibiotics to prevent anthrax is strongly discouraged unless you have been directly exposed to anthrax spores. Only those people who have been advised by their doctors and who have a clear indication that they have been exposed to spores are being given antibiotics. If antibiotics are overused or misused, bacteria can become resistant to them. In addition, antibiotics can cause side effects, such as nausea, vomiting, abdominal pain, and headaches.
The bioterrorism attacks in the United States in 2001 made many people understandably afraid to open their mail. But you can take steps to reduce your risk of exposure to anthrax.
The U.S. Centers for Disease Control and Prevention (CDC) has established methods for dealing with suspicious mail. If you receive a piece of mail that looks unusual, contains a powdery substance, or somehow seems suspicious, the CDC recommends that you:
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- Southwick FS (2004). Infections due to gram-positive bacilli. In DC Dale, DD Federman, eds., Scientific American Medicine, vol. 2, chap. 7, pp. 1–16. New York: WebMD.
- Government of Saskatchewan (2006). Human skin anthrax case confirmed in Saskatchewan. Government of Saskatchewan News Release, July 14, 2006. Available online: http://www.gov.sk.ca/news?newsId=1193e9c8-f864-4500-9111-e9d073c4cb55.
- Inglesby TV, et al. (2002). Anthrax as a biological weapon, 2002: Updated recommendations for management. JAMA, 287(17): 2236–2252.
- Centers for Disease Control and Prevention (2001). Considerations for distinguishing influenza-like illness from inhalational anthrax. MMWR, 50(44): 985–987. Available online: http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5044a5.htm.
- American Academy of Pediatrics (2009). Anthrax. In LK Pickering et al., eds., Red Book: 2009 Report of the Committee on Infectious Diseases, 28th ed., pp. 211–214. Elk Grove Village, IL: American Academy of Pediatrics.
- Lucey DR (2008). Anthrax. In L Goldman, D Ausiello, eds., Cecil Medicine, 23rd ed., vol. 2, pp. 2197–2200. Philadelphia: Saunders Elsevier.
Other Works Consulted
- American Public Health Association (2008). Anthrax. In DL Heymann, ed., Control of Communicable Diseases Manual, 19th ed., pp. 22–31. Washington, DC: American Public Health Association.
- Duchin J, Malone JD (2009). Anthrax section of Bioterrorism. In EG Nabel, ed., ACP Medicine, section 8, chap. 5, pp. 8–16. Hamilton, ON: BC Decker.
- Martin GJ, Friedlander AM (2010). Bacillus anthracis (anthrax). In GL Mandell et al., eds., Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases, 7th ed., vol. 2, pp. 2715–2725. Philadelphia: Churchill Livingstone Elsevier.
- Shadomy SV, Rosenstein NE (2008). Anthrax. In RB Wallace et al., eds., Wallace/Maxcy-Rosenau-Last Public Health and Preventive Medicine, 15th ed., pp. 1185–1194. New York: McGraw-Hill.
|Primary Medical Reviewer||Kathleen Romito, MD - Family Medicine|
|Primary Medical Reviewer||Donald Sproule, MD, CM, CCFP, FCFP - Family Medicine|
|Specialist Medical Reviewer||Christine Hahn, MD - Epidemiology|
|Last Revised||August 3, 2010|
Last Revised: April 3, 2012
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