Anthrax is an infectious disease due to a type of bacteria called Bacillus anthracis. Infection in humans most often involves the skin, gastrointestinal tract, or lungs.A.D.A.M.

Causes, incidence, and risk factors

Anthrax commonly affects hoofed animals such as sheep, cattle, and goats, but humans who come into contact with 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 spores touch a cut or scrape on the skin.

• It is the most common type of anthrax infection.
• The main risk is contact with animal hides or hair, bone products, and wool, or with infected animals. People most at risk for cutaneous anthrax include farm workers, veterinarians, and tannery and wool workers.

Inhalation anthrax develops when anthrax spores enter the lungs through the respiratory tract. It is most commonly contracted when workers breathe in airborne anthrax spores during processes such as tanning hides and processing wool.

Breathing in spores means a person has been exposed to anthrax, but it does not mean the person will have symptoms.

• The bacteria spores must "germinate" or sprout (the same way a seed might sprout before a plant grows) before the actual disease occurs. The process usually takes 1 to 6 days. Forty-three days is the longest known incubation period.
• Once the spores germinate, they release several toxic substances. These substances cause internal bleeding, swelling, and tissue death.

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.

Symptoms

Symptoms of anthrax differ depending on the type of anthrax.

Symptoms of cutaneous anthrax start 1 to 7 days after exposure:

• An itchy sore develops that is similar to an insect bite. This sore may blister and form a black ulcer (sore).
• The sore is usually painless, but it is often surrounded by swelling.
• A scab often forms, and then dries and falls off within 2 weeks. Complete healing can take longer.

Symptoms of inhalation anthrax:

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

Symptoms of gastrointestinal anthrax usually occur within 1 week and may include:

• Abdominal pain
• Bloody diarrhea
• Diarrhea
• Fever
• Mouth sores
• Nausea and vomiting (the vomit may contain blood)

Signs and tests

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

A culture of the skin, and maybe a biopsy, are done on the skin sores. The sample is looked at under a microscope to identify the anthrax germ.

Tests may include:

• Blood culture
• Chest CT scan or chest x-ray
• Spinal tap to check for infection around the spinal column (See:CSF culture)
• Sputum culture

Fluid or blood samples may be sent to a special laboratory for more testing, including PCR, immunofluorescence, and immunohistochemistry.

Treatment

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 with ciprofloxacin plus another drug, given through a vein (intravenously). The length of treatment is about 60 days for people who have been exposed to anthrax, because it may take spores that long to germinate.

Cutaneous (skin) anthrax is treated with antibiotics taken by mouth, usually for 7 to 10 days. Doxycycline and ciproflaxin are most often used.

Expectations (prognosis)

When treated with antibiotics, cutaneous anthrax is likely to get better. However, up to 20% of people who do not get treatment may die if anthrax spreads to the blood.

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.

Calling your health care provider

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

Prevention

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 military personnel and some members of the general public. It is given in a series of five 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.

References

1. Lucey DR, Anthrax. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 317.
2. Martin GJ, Friedlander Am. Bacillus anthracis (anthrax). In: Mandell GL, Bennett JE, Dolin R, eds. Principles and Practice of Infectious Diseases. 7th ed. Philadelphia, Pa: Elsevier Churchill Livingstone; 2009:chap 208.
3. Reissman DB, Whitney EA, Taylor TH Jr, et al. One-year health assessment of adult survivors of Bacillus anthracis infection. JAMA. 2004/291:1994-1998. [PubMed: 15113818]

Review Date: 6/9/2011.

Reviewed 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.