Plague
Plague, also known as the black death, is an acute infection caused by the gram-negative, nonmotile, nonsporulating bacillus Yersinia pestis (formerly called Pasteurella pestis).
Plague occurs in several forms. Bubonic plague, the most common, causes the characteristic swollen and sometimes suppurative lymph glands (buboes) that give this infection its name. Other forms include septicemic plague, a severe, rapid systemic form; and pneumonic plague, which can be primary or secondary to the other two forms.
Without treatment, mortality is about 60% in bubonic plague and approaches 100% in septicemic and pneumonic plagues. With treatment, mortality is approximately 18%, largely due to the delay between onset and treatment. The patient’s age and physical condition are also factors.
Causes
The bite of a flea from an infected rodent host—such as a rat, squirrel, prairie dog, or hare—is the typical transmission route to humans. Occasionally, transmission occurs from handling infected animals or their tissues. Bubonic plague is notorious for the historic pandemics in Europe and Asia during the Middle Ages, which in some areas killed up to two-thirds of the population. This form is rarely transmitted from person to person. However, the untreated bubonic form may progress to a highly contagious, secondary pneumonic form, which is transmitted by contaminated respiratory droplets. In the United States, the primary pneumonic form usually occurs after inhalation of Y. pestis in a laboratory.
Endemic areas in the United States are California, Utah, Arizona, Nevada, and New Mexico. Bubonic and pneumonic plague can occur.
Signs and symptoms
The three forms of plague vary in their incubation period, early symptoms, severity at onset, and clinical course.
Bubonic plague
With bubonic plague, the incubation period is 2 to 6 days. The milder form begins with malaise, fever, and pain or tenderness in regional lymph nodes, possibly associated with swelling. Lymph node damage (usually axillary or inguinal) eventually produces painful, inflamed, and possibly suppurative buboes. The classic sign of plague is an excruciatingly painful bubo. Hemorrhagic areas may become necrotic; in the skin, such areas appear dark—hence the name “black death.”
Bubonic plague can progress rapidly. A seemingly mildly ill person with fever and adenitis may become moribund within hours.
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