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Anthrax is caused by a bacterium known as Bacillus anthracis, which infects grazing herbivores, chiefly cattle, sheep, goats, and horses. When exposed to oxygen, the organism forms spores, which are resistant to heat, sunlight, and dessication and can survive for decades. Anthrax usually occurs in those handling infected animals or their products, including hides, hair, wool, or flesh. Spores are introduced through a break in the skin, leading to a small raised area on the skin which ulcerates and turns black. (The name anthrax is derived from the Greek word for coal.) When untreated, the illness may be complicated by high fevers, swelling of the area around the ulcer, enlargement of the regional lymph nodes, infection of the bloodstream, and death. However, the cure rate is high when appropriate antibiotics are given.
Rarely, inhalation of anthrax spores causes inhalational anthrax, known historically as Woolsorters' Disease, which progresses rapidly and is often fatal despite treatment. Inhalational anthrax begins with non-specific flu-like symptoms, including fever, malaise, fatigue, dry cough, and chest discomfort, followed by the abrupt onset of respiratory distress, cyanosis (purplish color), profuse sweating, confusion, and shock. The chief finding is hemorrhagic mediastinitis (bloody inflammation of the lymph nodes in the center of the chest). The chest film may show a widened mediastinum or effusions, but generally does not show infiltrates. Chest CT is often helpful in assessing the mediastinal lymph nodes, especially if plain chest films are non-diagnostic. The course is frequently complicated by hemorrhagic meningitis (blood in the spinal fluid).
The diagnosis of an anthrax skin infection is generally made by culturing the skin lesion, though cultures are usually negative after antibiotics have been given. Immunohistochemical staining of tissue specimens obtained from the edge of the skin lesion may be helpful. The diagnosis of inhalational anthrax is generally confirmed by positive blood cultures. The microbiology laboratory should be alerted that anthrax is to be ruled out, because most Bacillus species found in blood cultures are contaminants. If blood cultures are negative, serum and other body fluids may be sent for PCR. A nasal swab for culture or direct fluorescent antigen may be positive shortly after exposure to anthrax, but may be negative by the time of clinical illness.
Pending final culture results, initial therapy for inhalational anthrax should consist of cipro 400 mg every 12 hours or doxycycline 100 mg every 12 hours by vein, in combination with a second antibiotic. For children, the recommended dosages are cipro 5-7.5 mg/kg every 12 hours and doxycycline 2.5 mg/kg every 12 hours, up to the adult dosages. Data are limited, but other quinolones are likely to be equally effective. Options for the second antibiotic include rifampin, vancomycin, imipenem, chloramphenicol, penicillin and ampicillin, clindamycin, and clarithromycin (Biaxin), all of which have shown activity against the strains of anthrax recently isolated in the United States. After clinical improvement, treatment may be completed with either one or two drugs. Therapy should be continued for a total of 60-100 days. Penicillin should not be used alone for inhalational anthrax, even if the strain appears susceptible, because laboratory studies suggest the organism may become resistant during treatment. Steroids may be used as adjunct therapy in cases with extensive edema, respiratory compromise, or meningitis. Anthrax of the skin is usually treated with cipro or doxycycline alone. If the illness is complicated by extensive swelling or severe toxicity, a second antibiotic should be added, as for inhalational anthrax.
Because of potential adverse effects of prolonged use of cipro or doxycycline in children and pregnant women, penicillin or amoxicillin may be substituted for cipro or doxycycyline once the strain has been shown to be susceptible to penicillin and the patient is clinically improving. In pregnant women, cipro is thought to be preferable to doxycycline, because the latter drug may be associated with an increased risk of bone and dental abnormalities in the developing fetus.
Those exposed to anthrax spores should be promptly started on cipro 500 mg twice daily or doxycycline 100 mg twice daily by mouth, to be continued for 60 days. If the strain is found to be susceptible to penicillin, high-dose penicillin or amoxicillin may be given.
Anthrax vaccine may be effective, but supplies are limited and have been reserved for military personnel, laboratory workers, and those who have been exposed to anthrax spores. For pre-exposure immunization, a total of five intramuscular injections are recommended on day 0, week 4, and months 6, 12, and 18, followed by annual boosters. For previously unvaccinated persons who have been exposed to anthrax spores, a total of three subcutaneous injections are recommended at 0, 2, and 4 weeks, in conjunction with a 60 day course of antibiotics.
For the most recent recommendations concerning management of anthrax exposure, go to Anthrax as a Biological Weapon, 2002. For the most recent recommendations on the use of anthrax vaccine, see
Use of Anthrax Vaccine in the United States - Recommendations of the Advisory Committee on Immunization Practices, 2009 on the CDC website.
Anthrax is not transmissible from person-to-person. In the hospital, standard barrier precautions should be adequate (i.e. masks are not necessary once the diagnosis is confirmed).
From the World Health Organization (WHO)
Anthrax (overview for travelers)
Anthrax fact sheet
Guidance on anthrax: frequently asked questions
Guidelines for the Surveillance and Control of Anthrax in Humans and Animals
From the Centers for Disease Control (CDC)
Use of Anthrax Vaccine in the United States - Recommendations of the Advisory Committee on Immunization Practices, 2009
Frequently asked questions
Anthrax fact sheet
Emerging Infectious Diseases: Bioterrorism-Related Anthrax (special issue)
Notice to Readers: Use of Anthrax Vaccine in Response to Terrorism: Supplemental Recommendations of the Advisory Committee on Immunization Practices
Update: Investigation of Bioterrorism-Related Anthrax and Interim Guidelines for Clinical Evaluation of Persons with Possible Anthrax
Update: Investigation of Bioterrorism-Related Anthrax and Adverse Events from Antimicrobial Prophylaxis
Notice to Readers: Updated Recommendations for Antimicrobial Prophylaxis Among Asymptomatic Pregnant Women After Exposure to Bacillus anthracis
Notice to Readers: Update: Interim Recommendations for Antimicrobial Prophylaxis for Children and Breastfeeding Mothers and Treatment of Children with Anthrax
Notice to Readers: Additional Options for Preventive Treatment for Persons Exposed to Inhalational Anthrax
Public health updates
Anthrax of the Gastrointestinal Tract
From the U.K. Health Protection Agency
Anthrax - general information
Questions commonly asked by health care providers about anthrax (PDF)
Interim Guidelines for Action in the Event of a Deliberate Release (PDF)
From the Journal of the American Medical Association (JAMA)
Anthrax as a Biological Weapon
Anthrax as a Biological Weapon, 2002
From the New England Journal of Medicine (NEJM)
Anthrax (review article)
Recognition and Management of Anthrax - An Update (PDF), Morton S. Swartz
Images in Clinical Medicine - Cutaneous Anthrax Infection (PDF)
From Emerging Infectious Diseases
Bioterrorism-Related Inhalation Anthrax: The First 10 Cases Reported in the United States, J. Jernigan
Clinical Issues in the Prophylaxis, Diagnosis, and Treatment of Anthrax, D. Bell
Anthrax of the Gastrointestinal Tract, T. Sirisanthana and A. E. Brown
From the United States Department of Defense
Anthrax Information Resources
Medical Aspects of Chemical and Biological Warfare (PDF)
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