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Plague

Fact sheet N°267
Updated November 2014


Key facts

  • Plague can be a very severe disease in people, with a case-fatality ratio of 30%-60% if left untreated.
  • It was known as the "Black Death" during the fourteenth century, causing an estimated 50 million deaths.
  • Plague is caused by the bacteria Yersinia Pestis, a zoonotic bacteria, usually found in small animals and their fleas.
  • People infected with plague usually develop “flu-like” symptoms after an incubation period of 3-7 days.
  • There are 3 forms of plague infection depending on the route of infection: bubonic, septicaemic and pneumonic. Bubonic-characterized by painful swollen lymph nodes or ‘buboes’- is the most common form.
  • Plague epidemics have occurred in Africa, Asia, and South America but since the 1990s, most human cases have occurred in Africa.
  • In 2013 there were 783 cases reported worldwide, including 126 deaths
  • The 3 most endemic countries are Madagascar, the Democratic Republic of Congo and Peru.

Plague is an infectious disease caused by the bacteria Yersinia Pestis, a zoonotic bacteria, usually found in small animals and their fleas. It is transmitted between animals and humans by the bite of infected fleas, direct contact, inhalation and rarely, ingestion of infective materials.

Plague can be a very severe disease in people, with a case-fatality ratio of 30%-60% if left untreated. In 2013 there were 783 cases reported worldwide, including 126 deaths. Historically, plague was responsible for widespread pandemics with high mortality. It was known as the "Black Death" during the fourteenth century, causing an estimated 50 million deaths, approximately half of them in Asia and Africa and the other half in Europe, where a quarter of the population succumbed.

Signs and symptoms

People infected with plague usually develop “flu-like” symptoms after an incubation period of 3-7 days. Typical symptoms are the sudden onset of fever, chills, head and body-aches and weakness, vomiting and nausea.

There are 3 forms of plague infection, depending on the route of infection: bubonic, septicaemic and pneumonic.

  • Bubonic plague (known in mediaeval Europe as the ‘Black Death’) is the most common form of plague and is caused by the bite of an infected flea. Plague bacillus, Y. pestis, enters at the bite and travels through the lymphatic system to the nearest lymph node where it replicates itself. The lymph node then becomes inflamed, tense and painful, and is called a "bubo". At advanced stages of the infection the inflamed lymph nodes can turn into suppurating open sores.
  • Septicaemic plague occurs when infection spreads directly through the bloodstream without forming a “bubo". Septicaemic plague may result from flea bites and from direct contact with infective materials through cracks in the skin. Advanced stages of the bubonic form of plague will also lead to direct spread of Y. pestis in the blood.
  • Pneumonic plague-or lung-based plague- is the most virulent and least common form of plague. Typically, the pneumonic form is caused by spread to the lungs from advanced bubonic plague. However, a person with secondary pneumonic plague may form aerosolized infective droplets and transmit plague via droplets to other humans. Untreated pneumonic plague has a very high case-fatality ratio.

Where is plague found?

Plague is endemic in many countries in Africa, the former Soviet Union, the Americas and Asia. The distribution of plague coincides with the geographical distribution of the rodents it infects, which are found in all continents except Australia, within a broad belt in tropical, subtropical and warmer temperate climates. Plague epidemics have occurred in Africa, Asia, and South America but since the 1990s, most human cases have occurred in Africa. The 3 most endemic countries are Madagascar, the Democratic Republic of Congo and Peru.

Diagnosing plague

Diagnosis and confirmation of plague requires laboratory testing. The best way to confirm that a patient has plague is to identify Y Pestis in a sample of fluid from a bubo, or blood or sputum. Rapid dipstick tests have been validated for field use to quickly screen for Y. pestis antigen in patients. Specimens should be collected and forwarded to laboratories for plague testing.

Treatment

Untreated plague can be rapidly fatal so early diagnosis and treatment is essential for survival and reduction of complications. Antibiotics and supportive therapy are effective against plague if patients are diagnosed in time. These methods include the administration of antibiotics and supportive therapy.

Prevention

Preventive measures include informing people when zoonotic plague is active in their environment and advising them to take precautions against flea bites and not to handle animal carcasses in plague-endemic areas. People should also avoid direct contact with infected tissues such as suppurating buboes, or exposure to patients with pneumonic plague.

Vaccination

Plague vaccines were once widely used but have not been shown to be very effective against plague. Vaccines are currently not recommended during outbreaks but are still used for high-risk groups (e.g. laboratory personnel who are constantly exposed to the risk of contamination).

Managing plague outbreaks

  • Find and stop the source of infection: identify the most likely source of infection in the area where the human case(s) was exposed, typically looking for clustered areas with large numbers of small animal deaths. Institute appropriate sanitation and control measures to stop the exposure source.
  • Inform health workers: about where plague is being actively transmitted, what clinical features to look out for and what the plague case definition is.
  • Ensure correct treatment: verify that patients are being given appropriate antibiotic treatment and that local supplies of antibiotics are adequate.
  • Isolate patients with pneumonic plague.
  • Obtain specimens for laboratory confirmation.

Surveillance and control

Surveillance and control requires investigating animal and flea species implicated in the plague cycle in the region and developing environmental management programmes to limit spread. Active long-term surveillance of animal foci, coupled with a rapid response during animal outbreaks has successfully reduced numbers of human plague outbreaks.

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