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Microbiology and Immunology
Microbiology and Immunology 2500A/B

Lecture 3: Plague 09/12/2012 Plague  Incubation of 2-6 days, death in about 2-4 days  Patients experience sudden onset of fever, chills, headaches, muscle pain, weakness  Painful swellings (buboes) of the lymph nodes in the armpits, legs, neck, or groin  High fever, delirium and mental deterioration, large blackish pustules that burst, vomiting of blood, bleeding in the lungs Plague Pandemics  The “Plague of Justinian” – the first pandemic o Named after the Roman Emperor Justinian th o Started in the 6 century (541-542 AD) o Caused by Yersinia pestis (probably) o Spread to the Mediterranian, Italy and throughout Europe o About 50% of the population is estimated to have died o Continued in cycles for another 200 years until about 750 AD then disappears for ~800 years o Estimated to have killed 100 million people  The “Black Death” – the second pandemic o Medieval pandemic caused by Yersinia pestis o Originated in Asia and reached Europe in the late 1340s o Reduced the global population from about 450 million to 350-375 million o Killed about 25 million Europeans (1/3 of the total population) o Plague doctors – beak of the mask worn by them was loaded with herbs and such to avoid infection o 1348 – people had no idea what was happening o No (real) treatment, despite doctors (e.g. bloodletting), fear turned to panic o Standard treatment – frogs were placed on buboes o Many people believed this was due to “God's anger” or "Satan's influence" o Persecution of strangers, minorities, and witches o European social order, family structure, agriculture, the military and the feudal system, were destroyed  The Feudal System: o Political and social structure prevalent in Europe o Little opportunity for advancement o A few people had everything, most had little o Plague created vacant towns and farms, positions of authority need to be filled o Demand for physicians, clergy, gravediggers o Provided new opportunities for the peasants  Mid-19 Century – the third pandemic o Started in China in the 1850s and spread to all continents – considered active until 1959 o More than 12 million deaths in China and India alone o Reached San Francisco in 1900 – infected rats exchanged fleas with local wildlife – Y. pestis is now established in Southwestern U.S. Yersinia  Gram negative rods, facultative anaerobes  3 species pathogenic for humans: o Y. enterocolitica – causes "yersiniosis" – a rare cause of diarrhea and abdominal pain o Y. pseudotuberculosis – primarily an animal pathogen that can cause tuberculosis-like symptoms in animals, enteritis in humans o Y. pestis – cause of Plague Yersinia Pestis  Discovered independently by Alexandre Yersin and Shibasaburo Kitasato in 1894  Pestis – pestilence (contagious or infectious epidemic disease)  An extraordinarily virulent pathogen  Causes death in 2-4 days by sepsis and/or overwhelming pneumonia with respiratory failure  Not an efficient colonizer of humans Did Y. Pestis Really Cause the Black Death?  Samples of teeth from the bodies that carried the plague were taken – DNA was extracted from the teeth of these victims  Genome of Y. pestis was sequenced from teeth – thus, Y. pestis did cause the Black Death Pathogenesis of Yersinia Pestis  Organisms live in rodents and are transmitted by fleas  A “zoonotic” pathogen – diseases that are transferred from animals to humans are known as zoonotic pathogens  Y. pestis causes "blocking" in the flea  Biofilm formation in the proventriculus  "Starving fleas“ – blood cannot remain in fleas, thus fleas keep biting, spreading disease  Causes regurgitation of organisms  Very low infective dose (about 10 cells)  Y. pestis initially survives and grows in macrophages  Trafficked to the lymph nodes, which leads to swelling, which leads to buboes  Y. pestis continue to grow extracellularly  At the terminal stage of the disease, the blood contains high concentrations of bacterial cells  Essential for transmission as fleas take a blood meal Evolution of Yersinia Pestis  Y. pestis evolved from Y. pseudotubercul
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