Plague is rare in most developed countries (1,2)[C].

  • Except for pockets in the Southwest United States, endemic plague and transmission to humans is rare.
  • Plague outbreaks still occur in some less developed regions of the world.
  • The risk of imported cases and the concern for bioterrorism (pneumonic plague) remain public health and security concerns.


  • Acute infection due to Yersinia pestis
  • Sporadic, limited geographic distribution
  • In the Americas, Southwestern United States and Peru report several cases annually.
  • Epidemics are associated with war, famine, and natural disasters.
  • Primarily a disease of rats and other small vertebrates
  • Transmitted to humans by bites from infected fleas
  • Occasional human transmission in those handling infected tissues
  • Can be spread human-to-human through respiratory secretions
  • Infected cats transmit disease by biting, licking, or scratching human hosts.
  • Y. pestis is a potential bioweapon.
  • System(s) affected: hematologic, lymphatic, immunologic, pulmonary, skin/exocrine, sepsis
  • Synonym(s): black death


Predominant sex: male = female


  • Few cases (<10) are reported annually in the United States; typically as sporadic cases in rural areas of the Southwest in the spring, summer, or fall
  • The World Health Organization (WHO) reports 1,000 to 3,000 cases per year (3)[C].
  • 14% mortality rate in U.S. plague cases

Etiology and Pathophysiology

The pathophysiology of plague infection (e.g., bubonic, pneumonic, pharyngeal, meningeal, or septicemic) is determined by complex host–agent interactions. The clinical outcome depends on early diagnosis and specific therapy, to include supportive care and public health measures.

  • Y. pestis is transmitted after the bite from a flea previously infected through a rodent host. It is also transmitted secondarily through contact with infected tissue (e.g., ingestion of contaminated meat or handling infected tissue) or by aerosol (pneumonic). Organisms reach regional lymph nodes and cause hemorrhagic inflammation and “bubo” formation (lymph node enlargement–bubonic plague). Spread to bloodstream and release of endotoxin causes septicemic plague; pneumonic plague
  • Untreated bubonic plague may progress to secondary pneumonic plague, which can be spread by respiratory droplets.
  • Pneumonic plague and the other plague syndromes, such as septicemic plague, are rare but usually fatal.

Risk Factors

  • Exposure to rats or fleas
  • Close contact with infected cat
  • Close contact with pneumonic plague patient
  • Hunters who skin wild animals
  • Potential bioterrorism agent
  • Occupational risk: field workers, animal researchers, laboratory workers (handling Y. pestis)

General Prevention

  • Avoid contact with vectors, infected tissue, or aerosol droplets (e.g., confirmed pneumonic plague case).
  • Killed vaccine is available for people at high risk to reduce risk and/or severity; tetracycline can be used for prophylaxis. Vaccine is available from the Centers for Disease Control and Prevention.

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