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Plague is an infectious disease caused by the bacterium Yersinia pestis that affects humans and animals. This bacterium is found in rodents and their fleas and occurs in many areas of the world, including the United States.

Plague infection takes three primary forms:

  • Bubonic (most common form)
  • Pneumonic
  • Septicemic


Exposure varies depending on the form of plague.

  • Bubonic - occurs when an infected flea bites a person or when materials contaminated with Y. pestis enters a person through a break in the skin. This form of plague is not contagious.
  • Pneumonic - occurs when Y. pestis infects the lungs. It is caused by breathing in aerosolized plague. This form of plague is also spread by breathing in Y. pestis suspended in respiratory droplets from a person or animal with pneumonic plague. This usually occurs because of direct close contact with the ill person or animal. Pneumonic plague can also occur if a person with bubonic or septicemic plague is untreated and the bacteria spread to the lungs.
  • Septicemic - occurs when bacteria multiply in the blood. It can either occur by itself or as a secondary illness caused by complications from bubonic or pneumonic plague. When it occurs alone it is caused in the same ways as bubonic. This form of plague is not contagious.


Symptoms vary according to the form of plague.

  • Bubonic - The first symptoms appear 2 to 6 days after infection and include fever, headache, chills and weakness. Persons with bubonic plague also develop swollen, tender lymph glands called buboes.
  • Pneumonic - Symptoms usually appear in 2 to 4 days after exposure. Initial symptoms appear flu-like, such as high fever, cough and chills. Later symptoms include pneumonia and watery or bloody sputum (coughing up blood).
  • Septicemic - Symptoms usually occur in 2 to 6 days after infection. Initial symptoms include nausea, vomiting, fever and chills. Later symptoms include blood pressure, abdominal pain, shock and internal bleeding.


Treatment of plague with antibiotics must begin immediately to be effective. Early treatment of pneumonic plague is essential. To reduce the chance of death, antibiotics must be given within 24 hours of first symptoms.

Streptomycin, gentamicin, the tetracyclines and chloramphenicol are all effective against plague.

Provider Issue

Patients with pneumonic plague should be isolated.

Antibiotics for seven days are also recommended for people who have direct, close contact with those exposed to plague.

For more extensive information about these agents, please visit Centers for Disease Control and Prevention.

Page last updated: May 13, 2021