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As the United States and Soviet Union developed biological weapons programs in the 1950s and 1960s, they experimented with techniques to aerosolize plague particles that create pneumonic plague. The availability of this bacteria in microbe banks throughout the world coupled with high fatality rates and the potential for secondary spread make a biological attack using plague a serious concern.

An outbreak of plague caused by the use of a biological weapon would differ greatly from a naturally occurring epidemic. The size of a pneumonic plague epidemic following an aerosol attack would depend upon the amount of agent used, weather conditions, and how the agent is aerosolized and disseminated. But typically, the first pneumonic cases would appear within two days of exposure, with many people dying immediately after the onset of symptoms. The incubation period is generally about one to six days, depending on setting.

In 1970, the World Health Organization reported that a dissemination of fifty kilograms of the bacteria that causes plague in an aerosol cloud over a large urban area might result in 150,000 cases of pneumonic plague, with between 80,000 and 100,000 people requiring hospitalization and 36,000 deaths. No warning systems exist to detect such a cloud, so the first sign of a bioterrorist attack with plague would most likely be a sudden outbreak of patients showing severe symptoms.

Vaccines have been developed, however, and in a pre-exposure setting they appear to be effective to a degree in preventing bubonic plague. Untreated pneumonic plague, on the other hand, has a suspected mortality rate of nearly 100 percent. Research and development efforts for a vaccine to protect against pneumonic plague are ongoing, mainly due to concerns that bioterrorists will use this form of the plague to infect civilian populations via an aerosolized attack.

Spread of Plague

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