Plague (Black Death)

  • Medical Author:
    Melissa Conrad Stöppler, MD

    Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

  • Medical Editor: Steven Doerr, MD
    Steven Doerr, MD

    Steven Doerr, MD

    Steven Doerr, MD, is a U.S. board-certified Emergency Medicine Physician. Dr. Doerr received his undergraduate degree in Spanish from the University of Colorado at Boulder. He graduated with his Medical Degree from the University Of Colorado Health Sciences Center in Denver, Colorado in 1998 and completed his residency training in Emergency Medicine from Denver Health Medical Center in Denver, Colorado in 2002, where he also served as Chief Resident.

What causes plague?

The bacteria that cause plague are known as Yersinia pestis. In the natural state, the bacteria infect wild rodents. Plague can still be found in many areas of the world, but 95% of cases today occur in Madagascar and sub-Saharan Africa. The World Health Organization states that between 1,000-2,000 cases are reported each year worldwide, but there are estimated to be more cases that go unreported. The bacteria are found in the U.S. in semi-arid areas of the southwest. Fleas that feed off of infected animals transmit the bacteria to other animals. Rats, ground squirrels, mice, prairie dogs, chipmunks, voles, and rabbits are examples of animals that may carry the plague bacteria. The bacteria are believed to persist at a low level in natural populations of these animals. When a large number of infected wild rodents die, fleas that have bitten these animals may bite humans and domestic animals. Cats that are bitten usually become ill, and they may cough infectious droplets into the surrounding air. While infected dogs may not appear ill, they may still carry infected fleas into the home.

The last urban outbreak of flea-transmitted plague in the U.S. occurred in the 1920s. Plague in the U.S. is rare today but occasionally occurs in the southwestern portion of the country where wild rodents may be infected. Between 1900-2012, 999 confirmed or probable cases of plague occurred in the U.S.

What are risk factors for plague?

Risk factors for plague include being bitten by fleas as well as exposure to rodents. Scratches or bites from infected domestic cats are also a risk factor. Contact with individuals with pneumonic plague (pneumonia caused by the plague bacteria, see below) is also a risk factor for acquiring the infection.

What is the incubation period for plague?

Symptoms and signs of plague usually develop between two and seven days after acquiring the infection, although they may appear after only one day in cases of exposure to pneumonic plague.

Medically Reviewed by a Doctor on 10/8/2015

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