Bacillus anthracis, the bacterium causing anthrax is an obvious choice for a biological weapon because it is relatively easy to culture, and, under appropriate conditions, will form spores.

For maximum effect, these spores need to be delivered in an aerosol so that they are inhaled. The smaller the spores, the more dangerous the weapon, because they penetrate more deeply into a person's lungs.

B. anthracis is a gram-positive, soil-dwelling bacterium that can be picked up by grazing animals, and most natural infections occur through contact with animals or contaminated products. In addition to inhalation, B. anthracis spores can penetrate the skin through cuts and abrasions, or be ingested in food.

Once in the body, spores may germinate at the site of entry or may be engulfed by macrophages and carried to lymph nodes. There they germinate, multiply and enter the blood stream.

The bacterium has...

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