Anthrax is an infectious disease due to a bacterium called Bacillus anthracis. Infection in humans most often involves the skin, gastrointestinal tract, or lungs.
Causes of Anthrax
Anthrax commonly affects hoofed animals such as sheep, cattle, and goats. Humans who come into contact with infected animals can get sick with anthrax as well.
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.
- 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.
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 or eschar).
- 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
- Mouth sores
- Nausea and vomiting (the vomit may contain blood)
Tests and Exams
The tests to diagnose anthrax depend on the type of disease that is suspected.
A culture of the skin, and sometimes a biopsy, are done on the skin sores. The sample is looked at under a microscope to identify the anthrax bacterium.
Tests may include:
- Blood culture
- Chest CT scan or chest x-ray
- Spinal tap to check for infection around the spinal column
- Sputum culture
Fluid or blood samples may be sent to a special laboratory for more testing, including PCR, immunofluorescence, and immunohistochemistry.
Treatment of Anthrax
Inhalational anthrax is treated with a combination of antibiotics such as ciprofloxacin plus another medicine, which are given by IV (intravenously). Antibiotics are usually taken for 60 days by people who have been exposed to anthrax, because it can take spores that long to germinate.
Cutaneous (skin) anthrax is treated with antibiotics taken by mouth, usually for 7 to 10 days. Doxycycline and ciprofloxacin are most often used.
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.
When to Contact a Health Professional
Call your health care provider if you have been exposed to anthrax, or if you develop symptoms of any type of anthrax.
Prevention 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 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.
Lucey DR, Anthrax. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 302.
Martin GJ, Friedlander Am. Bacillus anthracis (anthrax). In: Mandell GL, Bennett JE, Dolin R, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 7th ed. Philadelphia, PA: Elsevier Churchill-Livingstone; 2009:chap.208.
|Review Date: 5/19/2013
Reviewed By: 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, Boston, MA. Also reviewed by David Zieve, MD, MHA, Bethanne Black, and the A.D.A.M. Editorial team.