Bubonic plague is one of three types of plague caused by the plague bacterium (Yersinia pestis). One to seven days after exposure to the bacteria, flu-like symptoms develop. These symptoms include fever, headaches, and vomiting, as well as swollen and painful lymph nodes occurring in the area closest to where the bacteria entered the skin. Acral necrosis, the dark discoloration of skin, is another symptom. Occasionally, swollen lymph nodes, known as "buboes," may break open.The three types of plague are the result of the route of infection: bubonic plague, septicemic plague, and pneumonic plague. Bubonic plague is mainly spread by infected fleas from small animals. It may also result from exposure to the body fluids from a dead plague-infected animal. Mammals such as rabbits, hares, and some cat species are susceptible to bubonic plague, and typically die upon contraction. In the bubonic form of plague, the bacteria enter through the skin through a flea bite and travel via the lymphatic vessels to a lymph node, causing it to swell. Diagnosis is made by finding the bacteria in the blood, sputum, or fluid from lymph nodes.Prevention is through public health measures such as not handling dead animals in areas where plague is common. While vaccines against the plague have been developed, the World Health Organization recommends that only high-risk groups, such as certain laboratory personnel and health care workers, get inoculated. Several antibiotics are effective for treatment, including streptomycin, gentamicin, and doxycycline.Without treatment, plague results in the death of 30% to 90% of those infected. Death, if it occurs, is typically within 10 days. With treatment, the risk of death is around 10%. Globally between 2010 and 2015 there were 3,248 documented cases, which resulted in 584 deaths. The countries with the greatest number of cases are the Democratic Republic of the Congo, Madagascar, and Peru.The plague is considered the likely cause of the Black Death that swept through Asia, Europe, and Africa in the 14th century and killed an estimated 50 million people, including about 25% to 60% of the European population. Because the plague killed so many of the working population, wages rose due to the demand for labor. Some historians see this as a turning point in European economic development. The disease is also considered to have been responsible for the Plague of Justinian, originating in the Eastern Roman Empire in the 6th century CE, as well as the third epidemic, affecting China, Mongolia, and India, originating in the Yunnan Province in 1855. The term bubonic is derived from the Greek word , meaning "groin".

Baron Kitasato Shibasaburō (北里 柴三郎, January 29 [O.S. 17 January] , 1853 – June 13, 1931) was a Japanese physician and bacteriologist. He is remembered as the co-discoverer of the infectious agent of bubonic plague in Hong Kong during an outbreak in 1894, almost simultaneously with Alexandre Yersin.

Kitasato was nominated for the first annual Nobel Prize in Physiology or Medicine in 1901. Kitasato and Emil von Behring, working together in Berlin in 1890, announced the discovery of diphtheria antitoxin serum. Von Behring was awarded the 1901 Nobel Prize because of this work, but Kitasato was not.