Bubonic plague is a zoonotic disease, circulating mainly among small rodents and their fleas, and is one of three types of infections caused by Yersinia pestis (formerly known as Pasteurella pestis), which belongs to the family Enterobacteriaceae. Without treatment, the bubonic plague kills about two out of three infected humans within 4 days.
The term bubonic plague is derived from the Greek word βουβών, meaning "groin." Swollen lymph nodes (buboes) especially occur in the armpit and groin in persons suffering from bubonic plague. Bubonic plague was often used synonymously for plague, but it does in fact refer specifically to an infection that enters through the skin and travels through the lymphatics, as is often seen in flea-borne infections.
Bubonic plague—along with the septicemic plague and the pneumonic plague, which are the two other manifestations of Y. pestis—is generally believed to be the cause of the Black Death that swept through Europe in the 14th century and killed an estimated 25 million people, or 30–60% of the European population. Because the plague killed so many of the working population, wages rose and some historians have seen this as a turning point in European economic development. 
The most infamous symptom of bubonic plague is an infection of the lymph glands (lymphadenitis), which become swollen and painful and are known as buboes. After being transmitted via the bite of an infected flea the Y. pestis bacteria become localized in an inflamed lymph node where they begin to replicate. Buboes associated with the bubonic plague are commonly found in the armpits, upper femoral, groin and neck region. Acral gangrene of the fingers, toes, lips and nose, is another common symptom. The black color of the necrotized tissue is the origin of the term "Black Death", the bubonic plague pandemic that swept Europe in the mid-fourteenth century.
Due to its bite-based form of infection, the bubonic plague is often the first step of a progressive series of illnesses. Bubonic plague symptoms appear suddenly, usually 2–5 days after exposure to the bacteria. Symptoms include:
Gangrene of the extremities such as toes, fingers, lips and tip of the nose.
Other symptoms include heavy breathing, continuous blood vomiting, aching limbs, coughing, and extreme pain. The pain is usually caused by the decay or decomposure of the skin while the person is still alive. Additional symptoms include extreme fatigue, gastrointestinal problems, lenticulae (black dots scattered throughout the body), delirium and coma.
Two other types of Y. pestis plague are pneumonic and septicemic. Pneumonic plague, unlike the bubonic or septicemic, induces coughing and is very infectious, allowing it to be spread person-to-person.
Bubonic plague is an infection of the lymphatic system, usually resulting from the bite of an infected flea, Xenopsylla cheopis (the rat flea). In very rare circumstances like the septicemic plague the disease can be transmitted by direct contact with infected tissue or exposure to a cough of another human. The fleas are often found on rodents such as rats and mice, and seek out other prey when their rodent hosts die. The bacteria form aggregates in the gut of infected fleas and this results in the flea regurgitating ingested blood, which is now infected, into the bite site of a rodent or human host. Once established, bacteria rapidly spread to the lymph nodes and multiply.
Y. pestis bacilli can resist phagocytosis and even reproduce inside phagocytes and kill them. As the disease progresses, the lymph nodes can haemorrhage and become swollen and necrotic. Bubonic plague can progress to lethal septicemic plague in some cases. The plague is also known to spread to the lungs and become the disease known as the pneumonic plague, This form of the disease is highly communicable as the bacteria can be transmitted in droplets emitted when coughing or sneezing.
Several classes of antibiotics are effective in treating bubonic plague. These include aminoglycosides such as streptomycin and gentamicin, tetracyclines (especially doxycycline), and the fluoroquinolone ciprofloxacin. Mortality associated with treated cases of bubonic plague is about 1-15%, compared to a mortality rate of 50-90% in untreated cases.
People potentially infected with the plague need immediate treatment and should be given antibiotics within 24 hours of the first symptoms to prevent death. Other treatments include oxygen, intravenous fluids, and respiratory support. People who have had contact with anyone infected by pneumonic plague are given prophylactic antibiotics.
Laboratory testing is required, in order to diagnose and confirm plague. Ideally, confirmation is through the identification of Y. pestis culture from a patient sample. Confirmation of infection can be done by examining serum taken during the early and late stages of infection. To quickly screen for the Y. pestis antigen in patients, rapid dipstick tests have been developed for field use.
See main article: Plague of Justinian, Black Death and Third plague pandemic. The first recorded epidemic ravaged the Byzantine Empire during the sixth century, and was named the Plague of Justinian after emperor Justinian I, who was infected but survived through extensive treatment. 
See main article: Black Death. In the Early Modern period (1340-1500,) Europe experienced the worst human disaster in its history when the Black Death (also known as the bubonic plague) hit in 1347, destroying a third of the population. It is commonly believed that society subsequently became more violent as the mass mortality rate cheapened life and thus increased warfare, crime, popular revolt, waves of flagellants, and persecution . The Black Death originated in or near China and spread from Italy and then throughout other European countries.New research suggests that it began in the spring of 1346 in the stepped region, where a plague reservoir stretches from the north-western shore of the Caspian Sea into southern Russia. The Mongols had cut off the trade route, the Silk Road, between China and Europe which halted spread of the Black Death from the east Russia towards western Europe. The epidemic began with an attack that Mongols launched on the Italian merchant's last trading station in the region, Caffa in the Crimea .In the autumn of 1346, plague broke out among the besiegers and from them penetrated into the town. When spring arrived, the Italian merchants fled on their ships, unknowningly carrying the Black Death. Carried by the fleas on rats, the plague initially spread to humans near the Black Sea and then outwards to the rest of Europe as a result of people fleeing from one area to another.
The plague victims had a 50/50 chance of surviving due to symptoms such as high fevers and internal bleeding that caused black spots and large tumors. “The victim feels a profound depression, and death usually comes after three to five days. ”
There were many ethno-medical beliefs of prevention methods for avoiding the Black Death. One of the most famous ideas was that by walking around with flowers in or around their nose people would be able to "ward off the stench and perhaps the evil that afflicted them." There were also many religious prevention methods. One such method used was to carve the symbol of the cross onto the front door of a house with the words "Lord have mercy on us" near it.
Pistoia, a city in Italy, even went as far as enacting rules and regulations on the city and its inhabitants to keep it safe from the Black Death. The rules stated that no one was allowed to visit any plague-infected area and if they did they were not allowed back into the city. Some other rules were that no linen or woolen goods were to be imported into the city and no corpses were to be buried in the city. However, no matter how strictly they were enforced, the rules never helped and the city eventually became infected.
Religion, specifically last rites, was one of the most important things to people during the Black Death. However, during the days of the plague, last rites were becoming harder and harder to receive. In the beginning of the plague there were not enough clergymen to offer last rites to everyone and eventually by the end; plague victims were simply denied last rites because the remaining holy men did not want to contract the fatal disease.
See main article: Miasma theory. Medieval doctors thought the plague was created by air corrupted by humid weather, decaying unburied bodies, and fumes produced by poor sanitation. The recommended treatment of the plague was a good diet, rest, and relocating to a non-infected environment so the individual could get access to clean air. This did help, but not for the reasons the doctors of the time thought. In actuality, because they recommended moving away from unsanitary conditions, people were, in effect, getting away from the rodents that harbored the fleas carrying the infection. Using the broad based antibiotic streptomycin has proven to be dramatically successful against the bubonic plague within 12 hours of infection .
thumb|upright|Directions for searchers, Pune plague of 1897
The next few centuries were marked by several local outbreaks of lesser severity. The Great Plague of Seville (1647), the Great Plague of London (1665–1666), the Great Plague of Vienna (1679), and the Great Plague of Marseille (1720), were the last major outbreaks of the bubonic plague in Europe.
The plague resurfaced in the mid-19th century; like the Black Death, the Third Pandemic began in Central Asia. The disease killed millions in China and India — a British colony at the time — and then spread worldwide. The outbreak continued into the early 20th century. In 1897, the city of Pune in India was severely affected by the outbreak.
In 1899, the island of Hawaii was also hit by the plague causing it to be brought over into the United States. The first evidence of the disease was found in Oahu's Chinatown. It is located very closely to the island's piers and because rats could stow away in the cargo ships they were able to transfer here from China without being seen. As the rats made their ways to the nearest city, people were starting to fall ill and on December 12, 1899 the first case was confirmed. The Board of Health then quickly thought of ways to prevent the disease from spreading even farther inland. Their solution was to burn any suspected buildings that might have been infected with the disease. On December 31, 1899 the board started the first fire. They had originally planned to burn only several buildings and thought they could control the flames as each building was finished, but the fire got out of control, burning down neighboring buildings. The resulting fire caused many of Chinatown's homes to be destroyed and an estimated 4,000 people were left homeless.
In 1994, a plague outbreak in five Indian states caused an estimated 700 infections (including 52 deaths) and triggered a large migration of Indians within India as they tried to avoid the plague.
Some of the earliest instances of biological warfare were said to have been product of the plague, as armies of the 14th century were recorded catapulting diseased corpses over the walls of towns and villages in order to spread the pestilence.
Later, plague was used during the Second Sino-Japanese War as a bacteriological weapon by the Imperial Japanese Army. These weapons were provided by Shirō Ishii's units and used in experiments on humans before being used on the field. For example, in 1940, the Imperial Japanese Army Air Service bombed Ningbo with fleas carrying the bubonic plague. During the Khabarovsk War Crime Trials, the accused, such as Major General Kiyashi Kawashima, testified that, in 1941, some 40 members of Unit 731 air-dropped plague-contaminated fleas on Changde. These operations caused epidemic plague outbreaks.