Plague is an infectious disease caused by the bacterium Yersinia pestis. Symptoms include fever, weakness and headache. Usually this begins one to seven days after exposure. There are three forms of plague. The difference between the forms of plague is the location of infection; in pneumonic plague the infection is in the lungs, in bubonic plague the lymph nodes, and in septicemic plague within the blood. In the bubonic form there is also swelling of lymph nodes, while in the septicemic form tissues may turn black and die, and in the pneumonic form shortness of breath, cough and chest pain may occur.
|Yersinia pestis seen at 200× magnification with a fluorescent label.|
|Symptoms||Fever, weakness, headache|
|Usual onset||1–7 days after exposure|
|Types||Bubonic plague, septicemic plague, pneumonic plague|
|Diagnostic method||Finding the bacterium in a lymph node, blood, sputum|
|Treatment||Antibiotics and supportive care|
|Medication||Gentamicin and a fluoroquinolone|
|Prognosis||~10% risk of death (with treatment)|
|Frequency||~600 cases a year|
Bubonic and septicemic plague are generally spread by flea bites or handling an infected animal. The pneumonic form is generally spread between people through the air via infectious droplets. Diagnosis is typically by finding the bacterium in fluid from a lymph node, blood or sputum.
Those at high risk may be vaccinated. Those exposed to a case of pneumonic plague may be treated with preventive medication. If infected, treatment is with antibiotics and supportive care. Typically antibiotics include a combination of gentamicin and a fluoroquinolone. The risk of death with treatment is about 10% while without it is about 70%.
Globally, about 600 cases are reported a year. In 2017, the countries with the most cases include the Democratic Republic of the Congo, Madagascar and Peru. In the United States, infections occasionally occur in rural areas, where the bacteria are believed to circulate among rodents. It has historically occurred in large outbreaks, with the best known being the Black Death in the 14th century, which resulted in more than 50 million deaths.