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Yersinia Pestis '' seen at 2000x magnification This bacterium, carried and spread by fleas, is the cause of the various forms of the disease plague
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The or ''bubonic fever'' is the best-known
Variant of the deadly
Infectious Disease caused by the
Enterobacteria ''
Yersinia Pestis ''. The epidemiological use of the term ''
Plague '' is currently applied to bacterial infections that cause ''
Bubo es'', although historically the medical use of the term plague has been applied to
Pandemic infections in general.
Bubonic plague is mainly a disease in
Rodent s and
Flea s. Infection in a human occurs when a person is bitten by a flea that has been infected by biting a rodent that has been infected by the bite of another infected flea. The bacteria multiply inside the flea, sticking together to form a plug that blocks its stomach and causes it to begin to starve. The flea then voraciously bites a host and continues to feed, even though it can not quell its hunger, and consequently the flea vomits blood tainted with the bacteria back into the bite wound. The bubonic plague bacterium then infects a new victim, and the flea eventually dies from starvation. Any serious outbreak of plague is usually started by other disease outbreaks in rodents, or a rise in the rodent population.
In
1894 , two bacteriologists,
Alexandre Yersin of
France and
Shibasaburo Kitasato of
Japan , independently isolated the bacterium in
Hong Kong responsible for the
Third Pandemic . Though both investigators reported their findings, a series of confusing and contradictory statements by Kitasato eventually led to the acceptance of Yersin as the primary discoverer of the organism. Yersin named it ''Pasteurella pestis'' in honor of the
Pasteur Institute , where he worked, but in 1967 it was moved to a new genus, renamed ''
Yersinia Pestis '' in honor of Yersin. Yersin also noted that rats were affected by plague not only during plague epidemics but also often preceding such epidemics in humans, and that plague was regarded by many locals as a disease of rats: villagers in China and India asserted that, when large numbers of rats were found dead, plague outbreaks in people soon followed.
In
1898 , the French scientist
Paul-Louis Simond (who had also come to China to battle the
Third Pandemic ) established the rat-flea
Vector that drives the disease. He had noted that persons who became ill did not have to be in close contact with each other to acquire the disease. In Yunnan, China, inhabitants would flee from their homes as soon as they saw dead rats, and on the island of Formosa (Taiwan), residents considered handling dead rats a risk for developing plague. These observations led him to suspect that the flea might be an intermediary factor in the transmission of plague, since people acquired plague only if they were in contact with recently dead rats, but not affected if they touched rats that had been dead for more than 24 hours. In a now classic experiment, Simond demonstrated how a healthy rat died of plague after infected fleas had jumped to it from a plague-dead rat.
