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Medical Author:

Charles Patrick Davis, MD, PhD

Charles Patrick Davis, MD, PhD

Dr. Charles "Pat" Davis, MD, PhD, is a board certified Emergency Medicine doctor who currently practices as a consultant and staff member for hospitals. He has a PhD in Microbiology (UT at Austin), and the MD (Univ. Texas Medical Branch, Galveston). He is a Clinical Professor (retired) in the Division of Emergency Medicine, UT Health Science Center at San Antonio, and has been the Chief of Emergency Medicine at UT Medical Branch and at UTHSCSA with over 250 publications.

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Medical Editor:

Mary D. Nettleman, MD, MS, MACP

Mary D. Nettleman, MD, MS, MACP

Mary D. Nettleman, MD, MS, MACP is the Chair of the Department of Medicine at Michigan State University. She is a graduate of Vanderbilt Medical School, and completed her residency in Internal Medicine and a fellowship in Infectious Diseases at Indiana University.

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Medical Editor:

Melissa Conrad Stöppler, MD

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.

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In this Article

• Plague facts
• What is plague?
• What is the history of the plague?
• What causes plague?
• How is plague spread?
• What are plague symptoms and signs?
• How is plague diagnosed?
• What is the treatment for the plague? What is the prognosis of the plague?
• How can plague be prevented?
• Is there a vaccine against plague?
• What research is being done on plague?
• Where can more information be found on plague?
• Plague Index

Infection with Y. pestis causes plague in humans. Y. pestis is a bacterium that is a gram-negative rod-shaped bacterium genetically related to Escherichia coli that resembles a "safety pin" when stained with certain chemicals and viewed with a microscope. In general, plague circulates in rodent populations where infected fleas on rodents transfer the bacteria to other rodents. When the rodent population invades human habitats or when humans invade rodent habitats, the infected fleas on the rodents will also bite humans. This flea bite begins the development of plague in an individual. However, once a human is infected, it is fairly easy for that person to infect other people with the organisms especially if they develop pulmonary infection because droplets containing Y. pestis from the lungs are expelled into the air and can infect other humans.

Figure 1: Picture of Yersinia pestis, showing bipolar staining or "safety pin" appearance. SOURCE: CDC/Courtesy of Larry Stauffer, Oregon State Public Health Laboratory

Plague is a zoonotic (animal to animal) disease that can be spread to humans by several methods. The usual way humans encounter plague is from getting a flea bite from a flea that has previously been infected from biting an animal where the disease is endemic. Most often this is attributed to a plague-infected rat population, but it could be from many other animals such as mice, prairie dogs, squirrels, and other rodents. Unfortunately, even domestic cats and dogs can become infected and potentially may transmit the disease to humans. Dead animals can still contain many viable Y. pestis; humans can become infected when they handle these animals; people should use caution when touching touch dead animals or even getting close to them as they may have fleas looking for another warm (human) body to bite. Human-to-human spread occurs easily by people with pneumonic plague as they can spread infected droplets expelled from the lungs to other people or to objects that are subsequently touched by others. Individuals with bubonic or septicemic plague can also transmit the disease, usually by direct or indirect contact with infected body fluids or objects that come in contact with these fluids. Spread of plague can be facilitated when conditions arise that encourage rat populations to rapidly increase. For example, when cities reduce or fail trash pickup for any extended time period, a rat population may flourish, and so may the flea population. Consequently, human behaviors (warfare, economic failures, urban expansion, and others) may augment the development of plague.