The Bubonic Plague

The bubonic plague is an infectious disease caused by bacteria that affects humans and some animals (mostly rats and prairie dogs). While, historically, the disease has killed millions of people worldwide, there are currently only 1,000 to 3,000 cases per year. The bubonic plague mortality rate is 50 to 90 percent if left untreated; it drops to 15 percent with early diagnosis and treatment with antibiotics.
 

What Is the Bubonic Plague?

The bubonic plague is an acute, infectious disease present in rodents, humans, and ectoparasites (fleas, lice).
 

History of the Bubonic Plague

Historically, the bubonic plague has destroyed entire civilizations. In the 1300s, the "Black Death," as it was called, killed approximately one-third (20 to 30 million) of Europe's population. The bubonic plague killed 12 million people in the mid-1800s in China. Thanks to better living conditions, antibiotics, and improved sanitation, the bubonic plague is rare these days, occurring in a few thousand people worldwide each year.
 

The Cause of the Bubonic Plague

The bubonic plague is caused by bacteria called Yersinia pestis. These plague bacteria are found mainly in rodents, particularly rats, and in the fleas that feed on them. Humans can also acquire the bubonic plague from rodent or flea bites.
 
(Click Plague and Animals for more information.)
 

Other Types of Plague

Besides the bubonic plague, there are two other kinds of plague:
 
These forms can occur in combination with the bubonic plague.
 
(Click Types of Plague for more information.)
 

Transmission of the Bubonic Plague

The bubonic plague is usually transmitted in one of three ways:
 
  • Direct contact with infected tissue or bodily fluids
  • Bites from infected rodent fleas
  • Inhaling infected droplets.
     

The Bubonic Plague Incubation Period

When a person becomes infected with the bacteria that cause bubonic plague, the bacteria begin to multiply within the body. This occurs in the lymph system. (The lymph, or lymphatic system, is a major component of your body's immune system. The organs within the lymphatic system are the tonsils, adenoids, spleen, and thymus.) Symptoms of the bubonic plague can begin within 1 to 6 days of being infected. The period between becoming infected and the start of plague symptoms is called the plague incubation period.
 

Symptoms of the Bubonic Plague

It is possible for a person to first develop bubonic plague symptoms, followed several days later by septicemic plague symptoms, and then pneumonic plague symptoms.
 
(Click Symptoms of Plague or Pictures of Plague to learn more about plague symptoms.)
 

Diagnosing the Bubonic Plague

If you think you have the bubonic plague, your doctor will ask a number of questions about your medical history and perform a physical exam before making a bubonic plague diagnosis. During the physical exam, the doctor will look at the skin and listen to the lungs for signs and symptoms of bubonic plague. If the doctor has a high suspicion that a person has bubonic plague, he or she will recommend certain tests.
 
Because several conditions share similar symptoms of plague, your doctor will consider these and rule them out before diagnosing the bubonic plague. Some of these conditions include:
 
  • Syphilis (a sexually transmitted disease)
  • Tularemia (a serious illness usually caused by animals)
  • Appendicitis
  • Hernia
  • Typhoid fever (a life-threatening illness caused by Salmonella)
  • Lymphogranuloma vernereum (a sexually transmitted disease affecting the lymph system)
  • Shigellosis (an infectious disease typically caused by unsanitary conditions)
  • Cat scratch fever (a disease associated with being scratched by a cat).
     

Treatment for the Bubonic Plague

If it is suspected that a person has the bubonic plague, treatment should be started even before lab tests come back, and the person should be hospitalized and placed in isolation. Bubonic plague treatment generally involves antibiotics. It is also important that people who have been in close contact with a patient who has bubonic plague be identified and evaluated.
 

Prognosis for the Bubonic Plague

The bubonic plague can quickly progress, possibly causing septicemic plague, or even develop into pneumonic plague, if it is not treated early. The bubonic plague mortality rate is 50 to 90 percent if not treated; the rate is 15 percent when diagnosed and treated early.
 

Preventing the Bubonic Plague

Outbreaks of the bubonic plague will most likely continue to occur in wild rodent hosts, and will probably continue to exist in its many localized geographic areas around the world. Attempts to eliminate the bubonic plague in wild rodents are costly and futile; therefore, bubonic plague prevention is directed toward reducing the threat of infection in humans in high-risk areas through three techniques:
 
  • Environmental management
  • Public health education
  • Preventive drug therapy.
     

How Common Is the Bubonic Plague?

Approximately 10 to 20 people in the United States develop the bubonic plague in rural areas of the southwestern United States each year from flea or rodent bites (especially from infected prairie dogs). About one in seven of those infected die from it. There has not been a case of person-to-person infection in the United States since 1924.
 
Worldwide, there have been small plague outbreaks in Asia, Africa, and South America. Globally, the World Health Organization (WHO) reports 1,000 to 3,000 cases of the bubonic plague every year. Current statistics show there were 2,118 cases in 2003 worldwide.
 
The bubonic plague occurs more frequently during spring and summer months and in people under the age of 20 (especially men).
 
(Click Where Is Plague? for more information.)
 
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Written by/reviewed by: Arthur Schoenstadt, MD
Last reviewed by: Arthur Schoenstadt, MD