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Plague Facts (cont.)

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What is plague? What is the history of plague?

Plague is a bacterial disease that is infamous for causing millions of deaths due to a pandemic (widespread epidemic) during the Middle Ages in Europe, peaking in the 14th century. Many historical references describe the illness, which has been referred to as the Black Death or a "pestilence in the air." The first reported plague pandemic began in 541 A.D. and lasted for over 200 years, killing an estimated 100 million people or more throughout the Mediterranean basin. The so-called Black Death, or pandemic of the Middle Ages, began in China and made its way to Europe, causing the death of 60% of the entire population. The third, or modern, pandemic started in China in the 19th century and spread to port cities all over the world. More recently, the World Health Organization reported an outbreak of plague in Madagascar in November 2014 and again from August through October 30, 2017, with a total of 1,801 confirmed, probable, and suspected cases of plague, including 127 deaths according to Madagascar health officials.

Rodents and many other kinds of animals can be infected with plague-causing bacteria. People contract the bacteria through bites of fleas that have fed on plague-infected rodents. Humans can also develop the infection from handling fluids or tissues from infected animals. People with pneumonic plague can also transmit the infection to other humans via coughing infectious droplets into the air.

What causes plague?

The bacteria that cause plague are known as Yersinia pestis. In the natural state, the bacteria infect wild rodents. Plague can still be found in many areas of the world, but 95% of cases today occur in Madagascar and sub-Saharan Africa. The World Health Organization states that between 1,000-2,000 cases are reported each year worldwide, but there are estimated to be more cases that go unreported. The Yersinia pestis bacteria are found in the U.S. in semi-arid areas of the southwest. Fleas that feed off of infected animals transmit the bacteria to other animals. Rats, ground squirrels, mice, prairie dogs, chipmunks, voles, and rabbits are examples of animals that may carry the plague bacteria. The bacteria are believed to persist at a low level in natural populations of these animals. When a large number of infected wild rodents die, fleas that have bitten these animals may bite humans and domestic animals. Cats that are bitten usually become ill, and they may cough infectious droplets into the surrounding air. While infected dogs may not appear ill, they may still carry infected fleas into the home.

The last urban outbreak of human cases of flea-transmitted plague in the U.S. occurred in the 1920s. Plague in the U.S. is rare today but occasionally occurs in the southwestern portion of the country (including Northern New Mexico, Northern Arizona, and Southern Colorado) where wild rodents may be infected. Between 1900-2012, 1,006 confirmed or probable cases of plague occurred in the U.S.

Medically Reviewed by a Doctor on 11/14/2017


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