plague, any contagious, malignant, epidemic disease, in particular the bubonic plague and the black plague (or Black Death), both forms of the same infection. These acute febrile diseases are caused by Yersinia pestis (Pasteurella pestis), discovered independently by Shibasaburo Kitasato and Alexandre Yersin in 1894, a bacterium that typically is transmitted to people by fleas from rodents, in which epidemic waves of infection always precede great epidemics in human populations. People may also contract the disease through direct contact with infected animals and persons. When the disease occurs in rodents or other wild mammals in rural or wooded areas where they are prevalent, it is known as sylvatic plague; when it occurs in urban animal populations, typically rats, it is called urban plague.
Bubonic plague, the most common form, is characterized by very high fever, chills, prostration, delirium, hemorrhaging of the small capillaries under the skin, and enlarged, painful lymph nodes (buboes), which suppurate and may discharge. Invasion of the lungs by the organism (pneumonic plague) may occur as a complication of the bubonic form or as a primary infection. Pneumonic plague is rapidly fatal and is spread from person to person (by droplet spray) without intermediary transmission by fleas. In the black form of plague, hemorrhages turn black, giving the term "Black Death" to the disease. An overwhelming infection of the blood may cause death in three or four days, even before other symptoms appear.
In untreated cases of bubonic plague the mortality rate is approximately 50%–60%; pneumonic plague is usually fatal if not treated within 24 hours. Such antibiotics as streptomycin and tetracycline greatly reduce the mortality rate, especially of bubonic plague. Vaccine is available for preventive purposes. Rodent control is important in areas of known infection.
The earliest known visitation of the plague to Europe may have occurred in Athens in 430 BC, but it is unclear if the disease that afflicated Athens was caused by Y. pestis. A disastrous epidemic occurred in the Mediterranean during the time of the Roman emperor Justinian; an estimated 25% to 50% of the population is reported to have succumbed. The most widespread epidemic began in Constantinople in 1334, spread throughout Europe (returning Crusaders were a factor), and in less than 20 years is estimated to have killed three quarters of the population of Europe and Asia. The great plague of London in 1665 is recorded in many works of literature. Quarantine measures helped contain the disease, but serious epidemics continued to occur even in the 19th cent. The disease is still prevalent in parts of Asia, and sporadically occurs elsewhere (approximately 2,500 cases worldwide annually). In Surat, India, in 1994, 5,000 cases of pneumonic plague were reported in an outbreak; an estimated 100 people died, and more than 400,000 people fled the city. Because the number of cases of plague has been increasing annually, it is categorized as a re-emerging infectious disease by the World Health Organization.
See P. Ziegler, The Black Death (1969); W. Whitman, Travel in Turkey, Asia Minor, Syria and Egypt (1971); R. S. Gottfried, The Black Death (1983); G. Twigg, The Black Death: A Biological Reappraisal (1985); R. Horrox, ed., The Black Death (1994); O. J. Benedictow, The Black Death 1346–1353: The Complete History (2004); W. Orent, Plague (2004); J. Aberth, The Black Death: The Great Mortality of 1348–1350 (2005); J. Kelly, The Great Mortality: An Intimate History of the Black Death (2005).