Anthrax

Definition

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

See also: Cutaneous anthrax; Inhalation anthrax

Causes, incidence, and risk factors

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

There are three primary 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.
• Gastrointestinal anthrax occurs when someone eats anthrax-contaminated meat. The disease usually develops within one week, and can affect the mouth, esophagus, intestines, and colon. The infection can spread to the bloodstream, and may result in death.

Anthrax is a potential agent for use as a biological weapon or for bio-terrorism. In 2001, bioterrorist activities involving the U.S. Postal Service infected 22 people with anthrax; 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 bio-terrorism experts have concluded that it is technologically difficult to use anthrax effectively as a weapon on a large scale.

Symptoms

• Cutaneous anthrax: Blister or ulcer that later forms a black scab; usually has extensive surrounding swelling
• Inhalation anthrax: Initial stage presents with fever, malaise, headache, cough, shortness of breath, and chest pain; Shock may occur in the second stage
• Gastrointestinal anthrax: Nausea and vomiting (may include blood), anorexia, and bloody diarrhea

Signs and tests

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

• If cutaneous anthrax is suspected, a culture of the skin lesion will be done to identify the bacteria that causes anthrax.
• If inhalational anthrax is suspected, a chest X-ray, blood cultures, sputum cultures, spinal tap for CSF culture, and gram stain may be performed. Samples may need to be sent to a special lab for more definitive testing, including PCR, immunofluorescence, and immunohistochemistry.

Treatment

The mainstay of treatment is early antibiotic therapy. Several antibiotics are effective, including penicillin, doxycycline, and ciprofloxacin (Cipro). 

When treating inhalation anthrax, a combination of antibiotics should be used, often starting with an intravenous form of Cipro plus another agent.

Cutaneous anthrax is treated with oral (pill-form) antibiotics.

The length of treatment is currently about 60 days, since it may take spores that long to germinate.

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

Expectations (prognosis)

When treated with antibiotics, the prognosis of cutaneous anthrax is excellent. Untreated, however, up to 20% of individuals may die, due to anthrax-related blood infections.  

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

The prognosis of gastrointestinal anthrax is also poor. A a high number of individuals die from this form of the disease.

Complications

• Cutaneous anthrax: Spread of infection into the bloodstream
• Inhalational anthrax: Hemorrhagic meningitis, mediastinitis, shock, and death
• Gastrointestinal anthrax: Hemorrhage, shock, and death

Calling your health care provider

Call your health care provider if you have had an exposure to anthrax, or if you develop signs and symptoms of cutaneous, inhalation, or gastrointestinal anthrax.

Prevention

There are two primary modes of prevention of anthrax.

For individuals who have been truly exposed to anthrax (but have no signs and symptoms of the disease), preventive antibiotics may be offered, such as ciprofloxacin, penicillin, or doxycycline, depending on the particular strain of anthrax.

An anthrax vaccine is available to selected military personnel, but not to the general public. It is given in a 6-dose series. There is no known transmission of cutaneous anthrax from person to person. Household contacts of individuals with cutaneous anthrax do not need antibiotics unless they have also been exposed to the same source of anthrax.

References

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.

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

Illustrations

Cutaneous anthrax

Cutaneous Anthrax

Inhalation Anthrax

Antibodies

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Wool sorter's disease; Ragpicker's disease ; wool sorter disease; disease ragpickers