Anthrax is an acute infectious disease caused by a bacterium, Bacillus anthrasis. It became especially prominent in 2001 when several human cases of anthrax were linked to deliberate exposure, raising concerns about the use of the bacteria as a biological weapon. Anthrax would make a rather effective biological weapon since the spores can remain dormant for many years, activating as soon as conditions become optimal, and it is very easy to contract the disease through inhalation, leading to the potential for mass dispersal through aircraft, explosives, or random package drops.

The disease was well known in the Ancient World, as writings and archaeological evidence suggest. It primarily affects farm animals, with cases of human anthrax being contracted from exposure to infected animals. Humans cannot pass anthrax onto each other, so the disease is not contagious, but it takes exposure to just a few spores to lead to a serious infection. Like other bacterial infections, anthrax is treated with antibiotics.

There are three kinds of anthrax: cutaneous, gastrointestinal, and inhalation. Cutaneous anthrax is contracted through cuts on the skin. It is characterized by a small sore which turns into a blister with a black center. Cutaneous anthrax has a relatively high survival rate, especially if it is caught early. Gastrointestinal anthrax is somewhat more serious. It is caused through ingestion of infectious material, such as poorly cooked meat. The patient may experience nausea, loss of appetite, diarrhea, and a severe fever; mortality rates from this form of anthrax vary widely from 25%-75%.

The most serious form of anthrax is inhalation anthrax, caused by inhaling infectious spores which may be stirred up in soil, scraped from animal material, or deliberately introduced into the environment. The mortality rate can be as high as 80%, with symptoms beginning as a low grade flu and developing into a cough. Since inhalation anthrax is relatively rare, it can be difficult to diagnose, especially when people are frightened and overloading clinics with normal cold and flu symptoms.

A vaccine is available for anthrax, although it is not widely used since the natural risk of contracting the disease is relatively low. People who work extensively with animals such as veterinarians and slaughterhouse workers may choose to be vaccinated, as do some microbiologists and researchers who may be exposed to anthrax in the course of their work. Active duty military are also vaccinated against anthrax, due to its potential use as a biological agent.