What is anthrax?
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 routine vaccination.
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 postal workers and media employees who were exposed to anthrax spores when handling mail.
Humans can develop four types of anthrax infection:
- Cutaneous anthrax, through a break in the skin
- Gastrointestinal anthrax, by eating contaminated food
- Inhalational anthrax, by breathing in spores
- Oropharyngeal (back of the throat) anthrax, also by eating contaminated food
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.
What causes anthrax?
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. It is possible that an open cutaneous sore could spread anthrax from person to person, but such transmission is rare.1 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.
- Cutaneous anthrax is spread through direct contact with spores, which usually enter the skin through a cut or scrape on the hands, fingers, or face. Half of the infections in the 2001 United States bioterrorist attacks were cutaneous.2
- Gastrointestinal and oropharyngeal anthrax are spread by eating contaminated meat products. This has occurred in developing regions such as Asia, the Middle East, and Africa, but not in North America.
- Inhalational anthrax spreads when a person breathes in spores. With inhalational anthrax, the smallest bacterial spores enter the tissues in the chest and lungs. The spores then multiply and enter the bloodstream. At this point, the disease becomes full-blown and very difficult to treat. It may take several days to weeks for this process to occur.
What are the symptoms?
The incubation period—the time from exposure to anthrax until symptoms develop—depends on the type of anthrax. In general, the symptoms depend on the type of infection.
- Cutaneous anthrax usually begins as a small, raised bump that might itch. The incubation period is usually 5 to 7 days, but it may be longer. Within 1 to 2 days, the bump develops into a painless, fluid-filled blister about 1 cm (0.4 in.) to 3 cm (1.2 in.) in diameter. Within 7 to 10 days, the blister has a black center of dying tissue—called an eschar—surrounded by redness and swelling. Swollen lymph nodes, headache, and fever also may occur.
- With inhalational anthrax, the first symptoms usually appear from 1 to 7 days after exposure to spores. But symptoms may not appear for as long as 60 days after exposure. Symptoms can resemble those of influenza (flu), including sore throat, mild fever, and muscle aches. But shortness of breath, which may occur with anthrax infection, is not common in the flu, and a runny nose, which often occurs with the flu, is not common with anthrax.3 Severe difficulty breathing, high fever, and shock develop 1 to 5 days after the first symptoms. Death occurs within 24 to 36 hours after shock develops.
- Symptoms of gastrointestinal anthrax, which usually occur 1 to 6 days after exposure to spores, include ulcers at the base of the tongue or tonsils, a sore throat, loss of appetite, vomiting, and fever. These symptoms can progress to abdominal pain, vomiting of blood, and bloody diarrhea. Within 2 to 4 days later, fluid (ascites) fills the abdomen; shock and death usually follow within 2 to 5 days.
- Within a week of exposure to oropharyngeal anthrax, the following symptoms develop: fever, swollen lymph nodes in the neck, severe sore throat, difficulty swallowing, and ulcers at the base of the tongue. As the infection progresses, swelling can make breathing difficult.
How is anthrax diagnosed?
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.
How is it treated?
All types of anthrax exposure can be treated effectively with antibiotics such as penicillin, doxycycline, or ciprofloxacin. 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.
Can anthrax be prevented?
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. The U.S. Advisory Committee on Immunization Practices recommends that only people at high risk of exposure receive the anthrax vaccine.
Frequently Asked Questions
Learning about anthrax:
When To Call a Doctor
If you think you have been exposed to anthrax spores, call your local law enforcement agency and your doctor immediately or contact your local or state health department. 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:
- Skin infection begins as a small, raised bump that might itch—similar to an insect or spider bite.
- Within 1 to 2 days, the bump develops into a fluid-filled blister about 1 cm (0.4 in.) to 3 cm (1.2 in.) in diameter. Within 7 to 10 days, the blister usually has a black center of dying tissue (eschar) surrounded by redness and swelling. The blister is usually painless.
- Additional blisters may develop.
Other symptoms may include:
- Swollen lymph nodes close to the area of the blister.
- A general feeling of discomfort.
No confirmed cases of gastrointestinal anthrax have been reported in the United States.2 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:
- Ulcers at the base of the tongue or tonsils.
- Sore throat.
- Loss of appetite.
These symptoms are followed by:
- Abdominal pain.
- Vomiting of blood.
- Bloody diarrhea.
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:
- Sore throat.
- Mild fever.
- Muscle aches.
Symptoms can progress rapidly after just a few days to include:
- Severe difficulty with breathing.
- Shock , which can develop rapidly.
- Meningitis , which develops frequently.
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 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:3
- Shortness of breath, which may occur with anthrax infection, is not a common symptom of the flu.
- A runny nose, which often occurs with the flu, is not common in anthrax.
This is the least common form of anthrax. The incubation period is from 1 to 7 days. Initial symptoms include:
- Swollen lymph nodes in the neck.
- Severe throat pain.
- Difficulty swallowing.
- Ulcers at the base of the tongue.
As infection progresses, swelling can make breathing difficult.
Exams and Tests
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, 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 has been approved by the U.S. Food and Drug Administration (FDA) 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 state and federal health departments 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 inhalational and cutaneous anthrax infection:1
Adults (including pregnant women) and children: Ciprofloxacin or doxycycline by mouth
Inhalational and gastrointestinal anthrax
Adults (including pregnant women) and children: Ciprofloxacin or doxycycline and one or two additional antibiotics, which might include rifampin, vancomycin, penicillin, ampicillin, chloramphenicol, imipenem, clindamycin, and clarithromycin. Initial treatment is by vein (intravenous, or IV), followed by medicine by mouth. The dosage of these medicines is reduced in children.
Considerations about medicine
- The treatment for inhalational anthrax also may be used for gastrointestinal and oropharyngeal infections.
- Although doxycycline and ciprofloxacin are usually not recommended for children or during pregnancy, experts say the need to treat a life-threatening illness outweighs the risks of taking these medicines.1 Potentially severe side effects to doxycycline in growing children include damage to dental enamel or possibly damage to formation of ligaments and cartilage. These medicines can cause staining and deformity of the teeth in newborns when given to women who are more than 4 months pregnant.
- Intravenous multidrug therapy is recommended to treat cutaneous anthrax infection if you have signs of wider infection, such as extensive fluids in tissues (edema) or lesions on the head and neck.
- Tests may be done to see if the anthrax bacteria can be killed by certain antibiotics. This is called sensitivity testing.
- Treatment of inhalational or gastrointestinal infection with penicillin alone is not recommended because the bacteria sometimes become resistant to penicillin.
- If the strain of bacteria is found to be susceptible to penicillin, children who might have been exposed to anthrax spores should be switched from doxycycline or ciprofloxacin to amoxicillin to prevent infection.1 Amoxicillin is a member of the penicillin (beta-lactam) family of medicines.
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.
Before exposure to anthrax
Currently, the vaccine is not recommended for or available to the public. The U.S. Advisory Committee on Immunization Practices has recommended that only people at high risk of exposure be given the anthrax vaccine. This includes some laboratory workers, people who come in contact with imported animals (such as veterinarians who travel to work in other countries), and military personnel. Pregnant women should be vaccinated only if absolutely necessary.
After exposure to anthrax
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.
How to Reduce Your Risk
The bioterrorism attacks 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 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:
- Carefully and immediately lay the piece of mail on the nearest flat surface, leave the room, wash your hands with soap and water, and call 911 to find out what to do next.
- Do not attempt to inspect the suspicious piece of mail by bringing it near your face to view or smell.
- Do not carry the piece of mail around your office or home to show others.
- Do not place the piece of mail in a plastic bag or other container as previously suggested by federal officials. This may cause a disturbance of anthrax spores in the piece of mail and potentially unleash spores into the air.
Other Places To Get Help
|Centers for Disease Control and Prevention (CDC)|
|1600 Clifton Road|
|Atlanta, GA 30333|
The Centers for Disease Control and Prevention (CDC) is an agency of the U.S. Department of Health and Human Services. The CDC works with state and local health officials and the public to achieve better health for all people. The CDC creates the expertise, information, and tools that people and communities need to protect their health—by promoting health, preventing disease, injury, and disability, and being prepared for new health threats.
- American Academy of Pediatrics (2006). Anthrax. In LK Pickering et al., eds., Red Book: 2006 Report of the Committee on Infectious Diseases, 27th ed., pp. 208–211. Elk Grove Village, IL: American Academy of Pediatrics.
- Southwick FS (2004). Infections due to gram-positive bacilli. In DC Dale, DD Federman, eds., Scientific American Medicine, section 7, chap. 4. New York: WebMD.
- Centers for Disease Control and Prevention (2001). Considerations for distinguishing influenza-like illness from inhalational anthrax. MMWR, 50(44): 985–987.
- 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 (2004). Anthrax. In DL Heymann, ed., Control of Communicable Diseases Manual, 18th ed., pp. 20–25. Washington, DC: American Public Health Association.
- Centers for Disease Control and Prevention (2002). Notice to readers: Use of anthrax vaccine in response to terrorism. Supplemental recommendations of the Advisory Committee on Immunization Practices. MMWR, 51(45): 1024–1026.
- Duchin J (2004). Anthrax section of Bioterrorism. In DC Dale, DD Federman, eds., ACP Medicine, section 8, chap. 5, pp. 7–13. New York: WebMD.
- Inglesby TV, et al. (2002). Anthrax as a biological weapon, 2002: Updated recommendations for management. JAMA, 287(17): 2236–2252.
- Lucey D (2005). Bacillus anthracis (anthrax). In GL Mandell et al., eds., Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases, 6th ed., pp. 2485–2491. Philadelphia: 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.
|Author||Maria G. Essig, MS, ELS|
|Editor||Susan Van Houten, RN, BSN, MBA|
|Associate Editor||Pat Truman, MATC|
|Primary Medical Reviewer||Kathleen Romito, MD - Family Medicine|
|Specialist Medical Reviewer||Christine Hahn, MD - Epidemiology|
|Last Updated||June 20, 2008|
Last Updated: June 20, 2008