Anthrax

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Topic Overview

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. However, 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. However, health professionals 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; they 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—is up to 7 days but can take 60 days or longer. In general, the symptoms depend on the type of infection.

• Cutaneous anthrax usually begins as a small, raised bump that might itch. Within 1 to 2 days, the bump develops into a painless, fluid-filled blister about to 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.
• Symptoms of gastrointestinal anthrax, which may occur within a week of 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.
• With inhalational anthrax, the first symptoms may appear from 2 to 3 days to 60 days or longer after exposure to spores. Symptoms can resemble those of influenza (flu), including sore throat, mild fever, and muscle aches. However, 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.
• 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 health professional 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 health professional 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 six 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 three doses of the vaccine 2 weeks apart.^{1, 4}

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.

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Last updated:	July 31, 2006
Author:	Sabra L. Katz-Wise
Reviewed By:	Renée M. Crichlow, MD - Family Medicine, W. David Colby, MSc, MD, FRCPC - Infectious Disease
Editors:	Susan Van Houten, RN, BSN, MBA, Pat Truman