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Topic Overview
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 inactive until they germinate.
Anthrax usually develops in cattle, horses, sheep, and goats. It is most common in underdeveloped agricultural regions of South and Central America, southern and eastern Europe, Asia, Africa, the Middle East, and the Caribbean.
Anthrax in humans is rare unless the spores are spread intentionally. Historically, anthrax infections in the United States occurred in people who worked with animals, such as veterinarians or ranchers. In 2001, the general population became concerned after 22 cases occurred 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
- Oropharyngeal (back of the throat) anthrax, also by eating contaminated food
- Inhalational anthrax, by breathing in the bacterial spores
Of the four types, inhalational is the most likely to cause death. Cutaneous anthrax is the most common form, while oropharyngeal anthrax is the least common.
How is anthrax spread?
The only way you can develop anthrax is from 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.
Cutaneous anthraxis spread through direct contact with bacterial spores, which usually enter the skin through a cut or scrape on the hands, fingers, or face. More than 95% of anthrax infections in the United States have been cutaneous.
Gastrointestinal and oropharyngeal anthrax are spread by eating contaminated meat products. The bacteria that cause anthrax can live in soil for many years. Animals may graze in fields with contaminated soil and become infected, and then humans may eat the infected meat. This has occurred in developing regions such as Asia, the Middle East, and Africa but not in the United States.
Inhalational anthrax spreads when a person breathes in spores. Once the spores germinate in a favorable environment in the respiratory tract, the body's immune system attempts to kill some of the spores. Other spores are carried to the lymph nodes in the chest. With inhalational anthrax, the smallest bacterial spores make their way into the tissues in the chest and lungs. The bacteria begin to 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 progression to occur.
People who are around those who have the disease do not need to be immunized or treated unless they were exposed to the same source of infection, such as a powder containing anthrax spores.
What are the symptoms of anthrax infection?
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 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 (eschar) surrounded by redness and swelling. Swollen lymph nodes, headache, and fever also may occur.
- With inhalational anthrax , initial symptoms can resemble those of influenza (flu), including sore throat, mild fever, and muscle aches. However, the symptoms of flu and inhalational anthrax differ in two key ways: 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. The initial symptoms of anthrax may appear from 2 to 3 days to 60 days or longer after exposure to spores. Severe difficulty breathing, high fever, and shock follow after 1 to 5 days. Death occurs within 24 to 36 hours after shock develops.
- Symptoms of gastrointestinal anthrax , which may develop within a week of exposure, 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. From 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 treated?
All types of anthrax exposure can be treated effectively with antibiotics such as penicillin, doxycycline, or ciprofloxacin. Prompt treatment may help reduce the potential 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.
Supportive treatment may be given in the hospital to help the body fight the infection. These measures include giving oxygen, fluids, and corticosteroids .
Researchers are studying an enzyme that, in mice, destroys the anthrax bacterium. The enzyme, called a lysin, comes from a type of virus (phage) that attacks bacteria. If given early to a person exposed to anthrax, the enzyme might be an effective treatment. More studies are needed to confirm the results.
Can anthrax be prevented?
Anthrax infection can be prevented by vaccination. Currently, however, the vaccine is neither recommended for nor available to the public.
The U.S. Advisory Committee on Immunization Practices recommends that only people at high risk of exposure be given the anthrax vaccine. Those at highest risk in the United States have previously included 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.
The vaccine also is being given to workers who helped decontaminate sites from the 2001 bioterrorist attacks and some investigators of those attacks. Experts are studying whether giving the vaccine along with antibiotics after exposure can help prevent anthrax more effectively than antibiotics alone.
The anthrax vaccine , given in a series of 6 injections over 18 months, plus annual boosters, does have potential side effects. These include fever, headache, joint pain, and fatigue.
Usually either ciprofloxacin or doxycycline is given to prevent infection in people known or believed to have been exposed to inhalational anthrax. In some cases other antibiotics may be used
