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Anthrax is an infectious disease caused by bacteria called Bacillus anthracis. Infection in humans most often involves the skin, the gastrointestinal tract, or the lungs.

Anthrax commonly affects hoofed animals such as sheep and goats, but humans who come into contact with the infected animals can get sick from anthrax, too. In the past, the people who were most at risk for anthrax included farm workers, veterinarians, and tannery and wool workers.

There are three main routes of anthrax infection:

• Cutaneous anthrax occurs when anthrax touches a cut or scrape on the skin.
• Inhalation anthrax develops when anthrax spores enter the lungs through the respiratory tract.
• Gastrointestinal anthrax occurs when someone eats anthrax-tainted meat.

Anthrax may be used as a biological weapon or for bioterrorism. In 2001, anthrax sent through the U.S. Postal Service infected 22 people; 7 survivors had confirmed cutaneous anthrax disease.

While at least 17 nations are believed to have a biological weapons program, it is unknown how many nations or groups are working with anthrax. Most bioterrorism experts have concluded that it is difficult to use anthrax effectively as a weapon on a large scale.

Symptoms of anthrax differ depending on the type of anthrax.

Symptoms of cutaneous anthrax:

• Blister or ulcer that later forms a black scab
• Blister or ulcer is usually surrounded by a lot of swelling

Symptoms of inhalation anthrax:

• Begins with fever, malaise, headache, cough, shortness of breath, and chest pain
• Shock may occur later

Symptoms of gastrointestinal anthrax usually develop within one week and can affect the mouth, esophagus, intestines, and colon. Symptoms may include:

• Nausea and vomiting (the vomit may include blood)
• Anorexia
• Bloody diarrhea

The tests to diagnose anthrax depend on the type of disease suspected.

Tests may include:

• Culture of skin sore to test for cutaneous anthrax
• Chest x-ray
• Sputum culture
• Spinal tap to check your spinal fluid for infection (See:CSF culture)
• Gram stain (staining a sample of tissue and looking at it under a microscope for the bacteria that cause anthrax infection)

Tissue or fluid samples may be sent to a special lab for more detailed testing, including immunofluorescence.

Most people with anthrax are treated with antibiotics. Several antibiotics are effective, including penicillin, doxycycline, and ciprofloxacin.

When treating inhalational anthrax, a combination of antibiotics should be used. Doctors often start treatment ciprofloxacin plus another drug, given through a vein (intravenously).

Cutaneous anthrax is treated with antibiotics taken by mouth, usually for 7 to 10 days.

The length of treatment for inhalation anthrax is currently about 60 days, since it may take anthrax spores that long to grow.

In the event of a bioterrorist attack, the National Pharmaceutical Stockpile is available to help provide antibiotics should a shortage occur.

When treated with antibiotics, cutaneous anthrax is likely to get better. However, up to 20% of people who do not get treatment may die due to anthrax-related blood infections.

People with second-stage inhalation anthrax have a poor outlook, even with antibiotic therapy. Up to 90% of cases in the second stage are fatal.

Gastrointestinal anthrax infection can spread to the bloodstream, and may result in death.

Cutaneous anthrax:

• Spread of infection into the bloodstream

Inhalational anthrax:

• Hemorrhagic meningitis
• Swelling of lymph nodes in the chest (mediastinal adenopathy)
• Fluid buildup in the chest (pleural effusion)
• Shock
• Death

Gastrointestinal anthrax

• Severe bleeding (hemorrhage)
• Shock
• Death

Call your health care provider if you have been exposed to anthrax, or if you develop symptoms of any type of anthrax.

There are two main ways to prevent anthrax.

For people who have been exposed to anthrax (but have no symptoms of the disease), doctors may prescribe preventive antibiotics, such as ciprofloxacin, penicillin, or doxycycline, depending on the strain of anthrax.

An anthrax vaccine is available to certain military personnel, but not to the general public. It is given in a series of six doses over 18 months. There is no known way to spread cutaneous anthrax from person to person. People who live with someone who has cutaneous anthrax do not need antibiotics unless they have also been exposed to the same source of anthrax.

Woolsorter's disease; Ragpicker's disease; Cutaneous anthrax; Inhalation anthrax; Gastrointestinal anthrax

Inglesby TV, O'Toole T, Henderson DA, et al. Anthrax as a Biological Weapon, 2002. JAMA.160;2002;287:2236-2252.

Lucey DR, Anthrax. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 317.

Updated by: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine; Jatin M. Vyas, MD, PhD, Assistant Professor in Medicine, Harvard Medical School, Assistant in Medicine, Division of Infectious Disease, Department of Medicine, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.