Anthrax is an acute disease caused by the bacterium Bacillus anthracis. Most forms of the disease are lethal, and it affects mostly animals. It is not contagious but can be transmitted through contact or consumption of infected meat. Effective vaccines against anthrax are available, and some forms of the disease respond well to antibiotic treatment.
Like many other members of the genus Bacillus, B. anthracis can form dormant endospores (often referred to as "spores" for short, but not to be confused with fungal spores) that are able to survive in harsh conditions for decades or even centuries. Such spores can be found on all continents, even Antarctica. When spores are inhaled, ingested, or come into contact with a skin lesion on a host, they may become reactivated and multiply rapidly.
Anthrax commonly infects wild and domesticated herbivorous mammals that ingest or inhale the spores while grazing. Ingestion is thought to be the most common route by which herbivores contract anthrax. Carnivores living in the same environment may become infected by consuming infected animals. Diseased animals can spread anthrax to humans, either by direct contact (e.g., inoculation of infected blood to broken skin) or by consumption of a diseased animal's flesh.
Anthrax does not spread directly from one infected animal or person to another; rather, it is spread by spores. These spores can be transported by clothing or shoes. The body of an animal that had active anthrax at the time of death can also be a source of anthrax spores. Owing to the hardiness of anthrax spores, and their ease of production in vitro, they are extraordinarily well suited to use (in powdered and aerosol form) as biological weapons. Such weaponization has been accomplished in the past by at least five state bioweapons programs — those of the United Kingdom, Japan, the United States, Russia, and Iraq — and has been attempted by several others.