For more general information see Bubonic plague.

Bubonic plague is an infectious disease that is believed to have caused several epidemics or pandemics throughout history. A major pandemic in historic times, called the Third Pandemic, began in China in 1855, spreading the bubonic plague to all inhabited continents, and ultimately killing more than 12 million people in India and China alone.

Casualty patterns indicate that waves of this pandemic may have been from two different sources. The first was primarily bubonic and was carried around the world through ocean going trade, through transporting infected persons, rats and cargos harboring fleas. The second, more virulent strain, was primarily pnuemonic in character with a strong person to person contagion. This strain was largely confined to Manchuria and Mongolia.

Researchers during the "Third Pandemic" identified plague vectors and the plague bacillus. In 1896, bacteriologist Alexandre Yersin isolated the responsible bacterium (yersinia pestis) and determined the common mode of transmission. The disease is caused by a bacterium usually transmitted by the bite of fleas from an infected host, often a black rat. The bacteria are transferred from the blood of infected rats to the rat flea (Xenopsylla cheopsis ). The bacillus multiplies in the stomach of the flea, blocking it. When the flea next bites a mammal, the consumed blood is regurgitated along with the bacillus into the bloodstream of the bitten animal. Any serious outbreak of plague is started by other disease outbreaks in the rodent population. During these outbreaks, infected fleas that have lost their normal hosts seek other sources of blood. The bacterium which causes this disease, the Yersinia pestis, was named for Yersin. His discoveries led in time to modern treatment methods.

See also

• Black Death
• Epidemics
• Medieval demography
• Plague
• Plague of Justinian

References

• Kelly, John. The Great Mortality: An Intimate History of the Black Death, the Most Devastating Plague of All Time. New York: HarperCollins Publishers Inc., 2005. ISBN 0060006927.
• McNeill, William H. Plagues and People. New York: Anchor Books, 1976. ISBN 0385121229.
• Orent, Wendy. Plague: The Mysterious Past and Terrifying Future of the World's Most Dangerous Disease. New York: Free Press, 2004. ISBN 0743236858.