Anthrax is an infectious disease caused by spores of the bacterium, Bacillus anthracis. The B. anthracis spores are highly resistant to inactivation and may be present in the soil, for example, for decades, occasionally infecting grazing animals that ingest the spores. Goats, sheep and cattle are examples of animals that may become infected. Human infection may occur by three routes of exposure to anthrax spores: cutaneous (through the skin), gastrointestinal (by ingestion), and pulmonary (inhalation). In North America, human cases of anthrax are infrequent. However, the United States military views anthrax as a potential biological terrorism threat because the spores are so resistant to destruction and can be easily spread by release in the air. The development of anthrax as a biological weapon by several foreign countries has been documented.

Human anthrax cases can occur in 3 forms. Cutaneous infection is the most common manifestation of anthrax in humans, accounting for more than 95 percent of cases. Ingestion of undercooked or raw, infected meat can cause gastrointestinal anthrax infection. Breathing in airborne spores may lead to inhalation anthrax. The mortality rates from anthrax vary, depending on exposure, and are approximately 20% for cutaneous anthrax without antibiotics and 25 - 75% for gastrointestinal anthrax; inhalation anthrax has a fatality rate that is 80% or higher. Cutaneous anthrax can usually be successfully treated with antibiotics and some antibiotics have also been approved for post-exposure prophylaxis.

The only known effective pre-exposure prevention against anthrax is the anthrax vaccine. The vaccine was developed from an attenuated strain of B. anthracis. The vaccine derives from the cell-free culture filtrate of this strain and, in its final formulation, is adsorbed onto an aluminum salt. A well controlled clinical trial using an anthrax vaccine similar to the licensed anthrax vaccine was conducted in U.S. mill workers processing imported animal hair. During the trial, 26 cases of anthrax were reported at the mills - five inhalation and 21 cutaneous cases. Of the five inhalation cases, two individuals had received the placebo, while three individuals were in the observational group. Four of the five people who developed inhalation anthrax died. No cases of inhalation anthrax occurred in anthrax vaccine recipients. Based upon a comparison between the anthrax vaccine and placebo recipients, the authors calculated a vaccine efficacy level of 92.5 percent.

The licensed anthrax vaccine, termed Anthrax Vaccine Adsorbed (or AVA) is recommended for individuals who may come in contact with animal products that may be contaminated with Bacillus anthracis spores and for individuals engaged in diagnostic or investigational activities which may bring them in contact with Bacillus anthracis spores. It is also recommended for persons at high risk, such as veterinarians and others handling potentially infected animals. There is only a single anthrax vaccine licensed in the U.S.; the vaccine is manufactured by Emergent BioDefense Operations Lansing Inc., located in Lansing, Michigan (Anthrax Vaccine Adsorbed (Biothrax) package insert). New vaccines using current technology are under development.

Because of biological warfare threats, the military has had an active vaccination program against anthrax.

References and Publications

Drug Preparedness and Response to Bioterrorism

Dixon, TC, et al. "Anthrax." New England Journal of Medicine, 341(11), 1999, pp. 815-826.

"Recommendations of the Advisory Committee on Immunization Practices: Use of Anthrax Vaccine in the United States." Morbidity and Mortality Weekly Report, Vol. 49(rr15), December 15, 2000, pp.1-20.

What's the Difference Between the Flu and Anthrax Symptoms?

CDC - Anthrax and Related Information

Note: Documents in PDF format require the Adobe Acrobat Reader®. If you experience problems with PDF documents, please download the latest version of the Reader®.

FEDERAL REGISTER Biological Products; Bacterial Vaccines and Toxoids; Implementation of Efficacy Review; Proposed Rule and Proposed Order - 12/15/2005 - (PDF)

FEDERAL REGISTER Biological Products; Bacterial Vaccines and Toxoids; Implementation of Efficacy Review; Anthrax Vaccine Adsorbed; Final Order - 12/15/2005 - (PDF)

FDA Issues Final Rule and Final Order Regarding Safety and Efficacy of Certain Licensed Biological Products Including Anthrax Vaccine - 12/30/2003

Anthrax Vaccines: Efficacy Testing and Surrogate Markers of Immunity Workshop - 4/23/2002

FDA Approves License Supplements for Anthrax Vaccine - 1/31/2002

The Anthrax Vaccine: Is it Safe? Does it Work? - Institute of Medicine - 2002

FDA Statement - Confirmatory anthrax testing at all its buildings show buildings are negative for anthrax - 11/5/2001

Federal Register Notice - Prescription Drug Products; Doxycycline and Penicillin G Procaine Administration for Inhalational Anthrax (Post-Exposure) - 11/2/2001 - (PDF)

Guidance for Industry - Recommendations for Assessment of Donor Suitability and Blood and Blood Product Safety in Cases of Possible Exposure to Anthrax - 10/17/2001 - (PDF)

Questions and Answers About Anthrax Prevention and Treatment - HHS News - 10/10/2001

Statement of Kathryn C. Zoon, Ph.D., Before the Committee on Armed Services, U.S. Senate - 7/12/2000

Written Statement for the Record by the FDA, DHHS, Before the Committee on Armed Services, U. S. Senate - 4/13/2000

Statement by Susan S. Ellenberg, Ph.D., Before the Subcommittee on National Security, Veterans Affairs, and International Relations Committee on Government Reform, U.S. House of Representatives - 7/21/1999

Updated: December 21, 2005