Plague (Black Death) facts

  • Plague is an infectious disease caused by the bacteria known as Yersinia pestis.
  • Plague has a high fatality rate, and people have described outbreaks for centuries.
  • In the Middle Ages, plague was known as the “Black Death.” It caused the death of 60% of the population of Europe during a pandemic (an epidemic of human disease that has spread through a large geographic area).
  • Transmission occurs via fleas that feed on infected animals, typically wild rodents.
  • There are three forms of plague in humans: bubonic plague, septicemic plague, and pneumonic plague.
  • The signs and symptoms of plague generally develop between two and seven days after a person acquires the infection. Symptoms and signs depend on the type of plague and include the following:
  • Antibiotics are the treatment of choice for plague and are most effective when given early in the course of disease.
  • There is no commercially available vaccine against plague.
  • Plague bacteria may be found in low levels in animals in the southwestern U.S.
  • Diagnosis of plague depends upon identifying the causative bacteria in fluid or tissue samples.

Plague & Bioterrorism

With bioterrorism, there may be the possibility of transmission of disease from one human to another (for example, measles, influenza, avian flu, smallpox, plague, and viral hemorrhagic fevers). In the case of either a bioterrorism attack or just a natural outbreak, it may be necessary to avoid contact with infected people or just remain inside for a period of time until the infected people are no longer contagious.

What is plague? What is the history of plague?

Plague is a bacterial disease that is infamous for causing millions of deaths due to a pandemic (widespread epidemic) during the Middle Ages in Europe, peaking in the 14th century. Many historical references describe the illness, which has been referred to as the Black Death or a “pestilence in the air.” The first reported plague pandemic began in 541 A.D. and lasted for over 200 years, killing an estimated 100 million people or more throughout the Mediterranean basin. The so-called Black Death, or pandemic of the Middle Ages, began in China and made its way to Europe, causing the death of 60% of the entire population. The third, or modern, pandemic started in China in the 19th century and spread to many parts of the world in port cities. More recently, the World Health Organization reported an outbreak of plague in Madagascar in November 2014 and again from August through October 30, 2017, with a total of 1,801 confirmed, probable, and suspected cases of plague, including 127 deaths according to Madagascar health officials.

Rodents and many other kinds of animals can be infected with plague-causing bacteria. People contract the bacteria through bites of fleas that have fed on plague-infected rodents. Humans can also develop the infection from handling fluids or tissues from infected animals. People with pneumonic plague can also transmit the infection to other humans via coughing infectious droplets into the air.


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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 Yersinia pestis bacteria are found in the U.S. in semi-arid areas of the southwest. Rat fleas (Xenopsylla species) 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 human cases 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 (including Northern New Mexico, Northern Arizona, and Southern Colorado) where wild rodents may be infected. Between 1900-2012, 1,006 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 is also a risk factor for acquiring the infection.

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What is the incubation period for plague?

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

What are plague symptoms and signs? What are the different types of plague?

The signs and symptoms of plague may take three forms:

1. Bubonic plague

In this form of the infection, bacteria infiltrate the lymph nodes, causing enlarged, painful, tender lymph nodes called buboes. Accompanying symptoms are fever, chills, headaches, and weakness. If not treated, the infection can spread to other areas of the body. This is the most common form seen in the few U.S. infections.

2. Septicemic plague

This form of plague is a result of plague bacteria entering the bloodstream. It can occur on its own or it may develop from bubonic plague. Symptoms include fever, chills, weakness, abdominal pain, and shock. There can be bleeding and tissue death, especially of the fingers and toes. These dying tissues may appear black, hence the name Black Death.

3. Pneumonic plague

In the pneumonic form of the illness, symptoms of other types of plague can be present, but the characteristic clinical picture of pneumonia is present. The plague bacteria spread to the lungs or infect the lungs directly when infected droplets in the air are inhaled. This is the only form of plague that can be transmitted from person to person. Shortness of breath, chest pain, fever, and cough with watery or bloody mucus production are symptoms of pneumonic plague.


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Is plague contagious? How does plague spread?

Bubonic and septicemic plague are only rarely spread from person to person; transmission occurs when fleas feed on infected rodents and then bite people. Transmission of pneumonic plague to another person typically requires direct and close (within 6 feet) contact with an infected person. Pneumonic plague is contagious because infected people can spread the bacteria via airborne droplets of respiratory secretions. This type of person-to-person spread of plague has not been reported in the U.S. since 1924, but it may still occur in some developing countries.

What is the contagious period for pneumonic plague?

Plague can be spread by the respiratory secretions of individuals with active infection of pneumonic plague. Though the exact contagious period is not definitively known, it is believed that patients in the early stage of pneumonic plague (the first 24 hours) pose little risk of transmitting the disease. However, patients in the final stages of pneumonic plague who are coughing up visible blood or pus pose a much higher risk of transmitting the disease.

How do physicians diagnose plague?

The diagnosis of plague is confirmed upon identifying Yersinia pestis organisms in a sample of blood or tissue (such as an aspirate from an enlarged lymph node) from the infected patient. Diagnostic tests rely on culturing the organism, demonstrating the surface proteins of the bacteria, or identifying genetic material of the bacteria. Tests to identify the body’s antibody response to the infection are also available.

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What is the treatment for plague?

Antibiotics are effective in treating plague. Examples of antibiotics that can be used include ciprofloxacin (Cipro, Cipro XR, Proquin XR), streptomycin, gentamicin (Garamycin), and doxycycline (Vibramycin, Oracea, Adoxa, Atridox). People with plague are very ill and may require additional treatment, including oxygen, respiratory support, and medications to maintain adequate blood pressure. Patients with pneumonic plague must be isolated while in treatment to avoid spreading the infection.

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What is the prognosis of plague?

Plague is a very serious disease that is often fatal. About 50% of people with bubonic plague die if their illness is not treated. Pneumonic plague is typically always fatal if untreated. With treatment, about half of people with pneumonic plague will survive. The earlier that antibiotic treatment is given, the better the chance for recovery.

Is it possible to prevent plague? Is there a plague vaccine?

There is no commercially available vaccine to prevent plague. It’s possible to lessen the chance of contracting plague by rodent-proofing, or reducing rodent habitat areas around the home, avoiding contact with wild rodents, and wearing gloves while handling carcasses of potentially infected animals. Use repellent for skin and clothing while outdoors or in areas where exposure to fleas is likely. DEET-containing repellent can be applied on skin or clothing, while permethrin can be applied to clothing. Use flea-control products on pets, and if pets are allowed to roam free in plague-endemic areas (such as the southwestern U.S.), do not allow them to sleep on the bed; this will decrease the chance of transmitting potentially infected fleas. Prophylactic antibiotics should be administered to individuals with known exposure to plague or for those who have come in direct contact with infected tissue or body fluids.

Could plague be used as a biological weapon?

Concerns about plague include the potential for its use as a biological weapon. In fact, Yersinia pestis has a history of being used as a weapon. Historical examples include the catapulting of infected corpses over city walls and dropping infected fleas from airplanes.

Medically Reviewed on 3/27/2019



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United States. Centers for Disease Control and Prevention. “Plague.” Nov. 27, 2018. <>.