Plague
Plague is an infectious disease caused by Yersinia pestis bacteria, usually found in small mammals and their fleas. The disease spreads between animals through flea bites.
Humans can also be infected with plague through 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.
Although plague has been responsible for widespread pandemics throughout history, including the so-called Black Death that caused over 50 million deaths in Europe during the fourteenth century, today it can be easily treated with antibiotics and the use of standard preventative measures.
Plague is found on all continents except Oceania but most human cases since the 1990s have occurred in Africa. Plague is endemic in some areas in the Democratic Republic of Congo and Madagascar.
People infected with plague usually develop influenza-like symptoms after an incubation period of 1–7 days. Symptoms include fever, chills, aches, weakness, vomiting and nausea.
There are 3 main forms of plague.
Bubonic plague is the most common and is caused by the bite of an infected flea. The plague bacillus, Y. pestis, enters at the bite and travels to the nearest lymph node, where it replicates. The lymph node becomes inflamed, tense and painful, and is called a bubo. With advanced infections, the inflamed lymph nodes can turn into pus-filled open sores. Bubonic plague cannot spread from human to human.
Septicaemic plague occurs when infection spreads through the bloodstream. It may result from flea bites or from direct contact with infected materials through cracks in the skin, or it may develop from another form of plague. It is a very severe form of the disease.
Pneumonic plague – or lung-based plague – is a severe form of plague. Typically, it is caused by the spread of advanced bubonic plague to the lungs. However, a person with pneumonic plague can spread the disease to others through infectious particles released into the air.
Untreated plague can be rapidly fatal, so early diagnosis and treatment are essential for survival and to reduce complications. Antibiotics and supportive therapy are effective against plague if patients are diagnosed in time.
Laboratory testing is required to confirm plague. This includes identifying the Yersinia pestis bacterium in a sample of pus from a bubo, blood or sputum.
WHO does not recommend vaccination except for people at high risk of exposure, such as laboratory personnel and health-care workers.
Prevention focusses on informing people when plague is present in animals in their area and providing advice on how they can protect themselves. People should avoid flea bites and refrain from handling animal carcasses. People, especially health workers, should also avoid direct contact with infected tissues such as buboes, and take precautions to prevent exposure when treating patients with pneumonic plague.
Country readiness checklist:
