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Western University
Microbiology and Immunology
Microbiology and Immunology 2500A/B
John Mc Cormick

Plague Nursery Rhymes and Plague Ring around the Rosy  refers to the swelling of lymph nodes (buboes) A pocket full of Posy  refers to people carrying around flowers and herbs to freshen the air (under the impression that the bad air was causing these problems) Ashes, Ashes  refers to the many dead bodies that had to be burned because they couldn’t bury them all They all fall down  refers to how everyone dies Plague (Bubonic) The incubation period lasts 2-6 days, and death occurs in about 2-4 days. Patients experience a sudden onset of fever, chills, headaches, muscle pains, and weakness. This is accompanied with painful swelling of the lymph nodes (buboes) in the armpits, leg, neck, or groin. The bubonic plague results in high fever, delirium and mental deterioration, large blackish pustules that burst, vomiting of blood, and bleeding of the lungs. Pandemics of Plague There are 3 pandemics of plague studied in this lecture: 1. The Plague of Justinian 2. The Black Death 3. Mid 19 Century Plague Pandemics: The Plague of Justinian (First Pandemic) th This plague was named after the Roman Emperor Justinian. It started in the 6 century (541-542 AD) and was probably caused by Yersinia pestis carried by infected fleas in rats. This spread throughout the Mediterranean, Italy, and Europe, killing ~50% of those infected. It continued in cycles for ~200 years until about 750 AD, then disappears for ~800 years  estimated to have killed 100 million people. Yersinia Properties:  G-  Rod-shaped  Facultative anaerobe There are 3 species of Yersinia that are pathogenic for humans: 1. Y. enterocolitica: causes “yersiniosis” which is a rare cause of diarrehea and abdominal pain 2. Y. pseudotuberculosis: primarily an animal pathogen that causes tuberculosis-like symptoms in animals, and enteritis in humans 3. Y. pestis: cause of Plague Yersinia pestis Y. pestis was discovered by Yersin and Kitasato in 1894. “Pestis” stands for pestilence, which is a contagious or infectious epidemic disease. Y. pestis is an extremely virulent pathogen and causes death in 2-4 days by sepsis and/or overwhelming pneumonia with respiratory failure. Note: Y. pestis is not an efficient colonizer of humans. Plague Pandemics: The Black Death (Second Pandemic) The “Black Death” referred to a medieval pandemic caused by Y. pestis. It originated in Asia and reached Europe in the Late 1340s. It reduced the global population from ~450 million to 350-375 million  killed ~25 million Europeans (1/3 of the total population). The plague doctors weren’t actual physicians; they did manual jobs and became doctors during the plague epidemic. They wore a beak to protect them from inhaling the organism, and a cloak to prevent them from contact with fleas (important for transmission). The striking feature was the beak however, which was filled with herbs and flowers to minimize the bad air and ward off the stench. In 1348, people had no idea what was happening. There was no real treatment, but people were bloodletting in hopes of curing the disease. Many people believed that this was God’s anger or Satan’s influence, and they were persecuting strangers, witches, and minorities to find someone to blame. As a result, European social order, family structure, agriculture, the military and the feudal system, were destroyed Feudal System The Feudal system was the political and social order prevalent in Europe. A few people had everything, and most people had nothing  very little opportunity for advancement (if you were a peasant, you would always be a peasant). The plague created vacant towns and farms, and positions of authority need to be filled. There was a demand for physicians, gravediggers, and clergy, and this gave peasants opportunities to move up in the system. The plague resulted in the disruption of the feudal system. Did Y. pestis really cause the Black Death? London, England has plague pits where known victims of the bubonic plague were buried. Researchers took the teeth of victims, ground them up, and were able to sequence the entire genome of Y. pestis. This technology only allowed them to capture sequences already known of Y. pestis so if there was something specific about the organism we wouldn’t know. Plague Pandemics: Mid 19 Century (Plague Pandemics) Started in the mid-1850s in China and spread to all continents (considered active until 1959). It reached San Francisco in the mid-1900s and infected rats exchanged fleas with local wildlife (Y. pestis is now established in Southwestern U.S.). It resulted in over 12 million deaths in China and India alone. Pathogenesis of Y. pestis Organisms live in rodents and are transmitted by fleas. The flea takes a blood meal from an infected rat and the flea now becomes infected with Y. pestis, causing a ‘blocking’ in the flea. This causes biofilm to form in the proventriculus (after the esophagus and before the midgut), so the fleas will try to take a blood meal but they cant get the blood into the stomach because it is blocked. The fleas begin to starve as a
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