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 1cm to 3cm 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?