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Plague

Fact sheet
Updated April 2017


Key facts

  • Plague is caused by the bacteria Yersinia pestis, a zoonotic bacteria, usually found in small mammals and their fleas.
  • People infected with plague usually develop "flu-like" symptoms after an incubation period of 1-7 days.
  • There are 2 main clinical forms of plague infection: bubonic and pneumonic. Bubonic is the most common form and is characterized by painful swollen lymph nodes or 'buboes'.
  • Plague can be a very severe disease in people, with a case-fatality ratio of 30%-60% for the bubonic type and is always fatal for the pneumonic kind, if left untreated.
  • 2010 – 2015 there were 3248 cases reported worldwide, including 584 deaths.
  • Currently, the 3 most endemic countries are Madagascar, the Democratic Republic of the Congo and Peru.

Plague is an infectious disease caused by the bacteria Yersinia pestis, a zoonotic bacteria, usually found in small mammals and their fleas. It is transmitted between animals from their fleas. Humans can be contaminated by the bite of infected fleas, through direct contact with infected materials or by inhalation.

Plague can be a very severe disease in people, particularly in its septicaemic and pneumonic forms, with a case-fatality ratio of 30%-100% if left untreated. The pneumonic form is invariably fatal unless treated early, is especially contagious and can trigger severe epidemics through person-to-person contact via droplets in the air.

From 2010 to 2015 there were 3248 cases reported worldwide, including 584 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 in Europe.

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 open sores filled with puss.
  • Pneumonic plague-or lung-based plague- is the most virulent form of plague. Incubation period can be as short as 24 hours. 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 is always fatal.
  • Septicaemic plague occurs when infection spreads through the bloodstream, following a bubonic or a pneumonic plague.

Where is plague found?

As an animal disease, plague is found in all continents, except Oceania. There is a risk of human plague wherever the presence of plague natural foci (the bacteria, an animal reservoir and a vector) and human population co-exist.

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

Confirmation of plague requires lab testing. The best practice is to identify Y Pestis in a sample of puss from a bubo, blood or sputum. A specific Y. pestis antigen can be detected by different techniques. One of them is a Rapid dipstick test, which was validated in the field and is now widely used in in Africa and South America, with the support of WHO.

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.

Prevention

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

Vaccination

WHO does not recommend vaccination, expect 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. Rodent and vector controls.
  • Protect health workers: inform and train them on infection prevention and control. Workers in direct contact with pneumonic plague patients must wear personal protective equipment and receive a chemoprophylaxis with antibiotics as long as they are exposed.
  • 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. They should be isolated so as not to infect others via air droplets.
  • Surveillance: identify and monitor close contacts of pneumonic plague patients and give them a 7 day chemoprophylaxis.
  • Obtain specimens which should be carefully collected and sent to labs for testing.
  • Ensure safe burial practices.

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.

WHO Response

WHO aims to prevent plague outbreaks by maintaining surveillance and supporting at-risk countries to develop preparedness plans. As the type of animal reservoir differs according to the region and influences the risk and conditions of human transmission, WHO has developed specific guidelines for the Indian sub-continent, South-America and Sub-Saharan Africa.

WHO promotes the use of rapid diagnostic tests in all endemic regions. WHO works with Ministries of Health to support countries facing outbreaks for field control activities.