What disease is caused by the bacterium Yersinia pestis?

Plague is the disease caused by the bacterium Yersinia pestis. It is an infectious disease with three principal forms: bubonic plague, septicemic plague, and pneumonic plague.

Yersinia pestis usually circulates among rodents and is commonly transmitted to people through the bite of an infected flea. Bubonic plague causes swollen, painful lymph nodes called buboes. Septicemic plague infects the bloodstream, while pneumonic plague affects the lungs and can spread through respiratory droplets. Prompt antibiotic treatment greatly improves the outlook.

The bacterium was identified during the 1894 plague epidemic in Hong Kong by Alexandre Yersin, a physician and bacteriologist associated with the Pasteur Institute. Japanese bacteriologist Kitasato Shibasaburō was investigating the same outbreak independently. The organism was initially named Pasteurella pestis and was renamed Yersinia pestis in 1944.

Plague is strongly associated with the Black Death, but it is not merely a medieval disease. The bacterium remains present in wildlife reservoirs, and modern cases still occur, particularly in parts of Madagascar, the Democratic Republic of the Congo, Peru, and the western United States. Malaria, typhoid, and cholera are caused by different pathogens.