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 vaccination with 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 only licensed anthrax vaccine, Anthrax Vaccine Adsorbed (AVA) or BioThraxTM is indicated for active immunization for the prevention of disease caused by Bacillus anthracis, in persons 18 – 65 years of age at high risk of exposure. The vaccine has been licensed since 1970 and is currently manufactured by Emergent BioDefense Operations Lansing Inc., located in Lansing, Michigan. Next-generation anthrax vaccines are under development by multiple manufacturers.
BioThraxTM has been purchased by the federal government and is stored in the Strategic National Stockpile (SNS) to be used as part of a post-exposure prophylaxis regimen with licensed antibiotics in the event of a terrorist attack with anthrax. Likewise, because of biological warfare threats, the military has an active vaccination program against anthrax for personnel going to specific arenas around the world.
CBER continues to work with multiple manufacturers in the development of immune globulins as a potential treatment for anthrax infection.