A disease of soil, animals, and people, anthrax has threatened lives for at least two thousand years. Farmers have long recognized its lasting virulence, but in our time, anthrax has been associated with terrorism and warfare. What accounts for this frightening transformation? Death in a Small Package recounts how this ubiquitous agricultural disease came to be one of the deadliest and most feared biological weapons in the world.

Bacillus anthracis is lethal. Animals killed by the disease are buried deep underground, where anthrax spores remain viable for decades or...