plague

Introduction

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, and from fleas and lice from infected 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.

Sections in this article:

Introduction
History
Bibliography

See more Encyclopedia articles on: Pathology