Throughout recorded history Yersinia pestis has been the cause of multiple human pandemics and countless deaths. Plague is now endemic worldwide yet is responsible for only sporadic human disease (200-4500 human cases with 30-200 deaths reported to the WHO annually). The United States worked with Y. pestis as a potential BW agent in the 1950s and 1960s before the old offensive BW program was terminated. Other countries are suspected of having weaponized this organism. The former Soviet Union had several separate institutes and thousands of scientists dedicated to researching and weaponizing plague. During World War II, Unit 731, of the Japanese Army, reportedly released plague-infected fleas from aircraft over Chinese cities. This method was cumbersome and unpredictable. The U.S. and Soviet Union developed the more reliable and effective delivery method of aerosolizing the organism. The terrorist potential of plague was brought to light in 1995 when Larry Wayne Harris was arrested in Ohio for the illicit procurement of a Y. pestis culture through the mail. The contagious nature of pneumonic plague makes it particularly concerning as a biological weapon.

Plague is one of the oldest identifiable diseases known to man (see References: WHO: Plague manual). Three plague pandemics have been recorded throughout history (see References: WHO 2000), with an estimated 200 million deaths (see References: Perry 1997). Brief descriptions of the three pandemics follow.

  • The first pandemic started in Egypt in 542 AD and continued for more than a century. Outbreaks in Europe, Central and Southern Asia, and Africa killed an estimated 100 million people.
  • The second pandemic began in Italy in 1347 and rapidly spread throughout Europe over the next several years, killing an estimated one third of the European population. During that time, plague became known as the Black Death. Outbreaks of plague continued to occur sporadically in Europe over the next several centuries.
  • The third pandemic began in 1894 in China and spread around the world over a 10-year period, predominantly by infected rats and their fleas aboard steamships. An estimated 12 million deaths occurred, mostly in India.

Although bubonic plague historically has been the most common form of disease, large outbreaks of pneumonic plague (with person-to-person transmission as the primary mode of spread) also have been reported (see References: Kool 2005, Meyer 1961).

  • Two large outbreaks of pneumonic plague occurred in Manchuria in the early 20th century (1910-1911 and 1920-1921). An estimated 60,000 deaths occurred in the former and an estimated 9,300 in the latter.
  • Two pneumonic plague outbreaks occurred in the United States in the early 1900s (see References: Anderson 1978, Kool 2005). The first occurred in 1919 in Oakland, California. The index case was a hunter who contracted bubonic plague from an infected squirrel. He subsequently developed plague pneumonia and transmitted the disease to 12 or 13 other persons. A second outbreak occurred in Los Angeles in 1924 and involved 39 cases of pneumonic plague.
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