Last Editorial Review: 1/16/2008


Plague is an infectious disease caused by bacteria called Yersinia pestis. These bacteria are found mainly in rodents, particularly rats, and in the fleas that feed on them. Other animals and humans usually contract the bacteria from rodent or flea bites.

Historically, plague 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. In the mid-1800s, it killed 12 million people in China. Today, thanks to better living conditions, antibiotics, and improved sanitation, current World Health Organization statistics show there were only 2,118 cases in 2003 worldwide.

Approximately 10 to 20 people in the United States develop plague each year from flea or rodent bites—primarily from infected prairie dogs—in rural areas of the southwestern United States. About 1 in 7 of those infected die from the disease. 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.

Forms of Plague

Y. pestis can affect people in three different ways: bubonic, septicemic, or pneumonic plague.

Bubonic plague

In bubonic plague, the most common form, bacteria infect the lymph system and become inflamed. (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.)

How do you get it?

Usually, you get bubonic plague from the bite of an infected flea or rodent. In rare cases, Y. pestis bacteria, from a piece of contaminated clothing or other material used by a person with plague, enter the body through an opening in the skin.

What are the symptoms?

Bubonic plague affects the lymph nodes (another part of the lymph system). Within 3 to 7 days of exposure to plague bacteria, you will develop flu-like symptoms such as fever, headache, chills, weakness, and swollen, tender lymph glands (called buboes—hence the name bubonic).

Is it contagious?

Bubonic plague is rarely spread from person to person.

Septicemic plague

This form of plague occurs when the bacteria multiply in the blood.

How do you get it?

You usually get septicemic plague the same way as bubonic plague—through a flea or rodent bite. You can also get septicemic plague if you had untreated bubonic or pneumonic plague.

What are the symptoms?

Symptoms include fever, chills, weakness, abdominal pain, shock, and bleeding underneath the skin or other organs. Buboes, however, do not develop.

Is it contagious?

Septicemic plague is rarely spread from person to person.


Bacterial Infections 101: Types, Symptoms, and Treatments See Slideshow

Pneumonic plague

This is the most serious form of plague and occurs when Y. pestis bacteria infect the lungs and cause pneumonia.

How do you get it?

You get primary pneumonic plague when you inhale plague bacteria from an infected person or animal. You usually have to be in direct or close contact with the ill person or animal. You get secondary pneumonic plague if you have untreated bubonic or septicemic plague that spreads to your lungs.

What are the symptoms?

Symptoms usually develop within 1 to 3 days after you are exposed to airborne droplets of plague bacteria. Pneumonia begins quickly, with shortness of breath, chest pain, cough, and sometimes bloody or watery sputum. Other symptoms include fever, headache, and weakness.

Is it contagious?

Pneumonic plague is contagious. If someone has pneumonic plague and coughs, droplets containing Y. pestis bacteria from their lungs are released into the air. An uninfected person can then develop pneumonic plague by breathing in those droplets.


Y. pestis is found in animals throughout the world, most commonly in rats but occasionally in other wild animals, such as prairie dogs. Most cases of human plague are caused by bites of infected animals or the infected fleas that feed on them. In almost all cases, only the pneumonic form of plague (see Forms of Plague) can be passed from person to person.


A health care provider can diagnose plague by doing laboratory tests on blood or sputum, or on fluid from a lymph node.


When plague is suspected and diagnosed early, a health care provider can prescribe specific antibiotics (generally streptomycin or gentamycin). Certain other antibiotics are also effective.

Left untreated, bubonic plague bacteria can quickly multiply in the bloodstream, causing septicemic plague, or even progress to the lungs, causing pneumonic plague.



Health experts recommend antibiotics if you have been exposed to wild rodent fleas during a plague outbreak in animals, or to a possible plague-infected animal. Because there are so few cases of plague in the United States, experts do not recommend taking antibiotics unless it's certain a person has been exposed to plague-infected fleas or animals.


Currently, there is no commercially available vaccine against plague in the United States.


The National Institute of Allergy and Infectious Diseases (NIAID) conducts and supports research on the diagnosis, prevention, and treatment of infections caused by microbes, including those that have the potential for use as biological weapons. The research program to address biodefense includes both short- and long-term studies targeted at designing, developing, evaluating, and approving specific tools (diagnostics, drugs, and vaccines) needed to defend against possible bioterrorist-caused disease outbreaks.

For instance, NIAID-supported investigators sequenced the genome of the strain of Y. pestis that was associated with the second pandemic of plague, including the Black Death. This will provide a valuable research resource to scientists for identifying new targets for vaccines, drugs, and diagnostics for this deadly pathogen.

NIAID-funded scientists have developed a rapid diagnostic test for pneumonic plague that can be used in most hospitals. This will allow health care providers to quickly identify and isolate the pneumonic plague patient from other patients and enable health care providers to use appropriate precautions to protect themselves.

Many other plague research projects at NIAID are focusing on early-stage vaccine development, therapeutics, and diagnostics. Y. pestis bacterium is a high priority with funded efforts ranging from basic science research to final product development.

Current research projects include:

  • Identifying genes in Y. pestis that infect the digestive tract of fleas and researching how the bacteria are transferred to humans

  • Studying the disease-causing proteins and genes of Y. pestis that allow the bacteria to grow in humans and learning how they function in human lungs

NIAID is also working with the U.S. Department of Defense, the Centers for Disease Control and Prevention, and the U.S. Department of Energy to:

  • Develop a vaccine that protects against inhalationally acquired pneumonic plague

  • Develop promising antibiotics and intervention strategies to treat and prevent plague infection

Related Links

Government Links

National Library of Medicine MedlinePlus
8600 Rockville Pike
Bethesda, MD 20894
1-888-FIND-NLM (1-888-346-3656) or 301-594-5983

Centers for Disease Control and Prevention
1600 Clifton Road NE
Atlanta, GA 30333
1-800-311-3435 or 404-639-3534

Non-government Links

World Health Organization
Avenue Appia 20
CH-1211 Geneva 27

SOURCE: U.S. National Institutes of Health, National Institute of Allergy and Infectious Diseases (NIAID)


Bowel regularity means a bowel movement every day. See Answer

Health Solutions From Our Sponsors

SOURCE: U.S. National Institutes of Health, National Institute of Allergy and Infectious Diseases (NIAID)