Scientific+Context+of+the+Third+Plague

**What is the plague?**

 The plague is a disease of rodents that can be spread to humans by the transmission of infected fleas. The plague has three different forms, (1) bubonic plague which is the infection of the lymph glands, (2) septicaemia plague which is the infection of the blood and (3) pneumonic plague which is the infection of the lungs. It can spread by bites of infected fleas by either direct contact with the tissues or body fluids of a plague infected animal. It can also be transmitted by inhaling infectious airborne droplets from a person or animal with pneumonia plague or by laboratory exposure to the plague bacteria [1].



 At the University of Chicago a researcher died after being exposed to a strain of bacteria that causes the plague on September 21st, 2009. Professor Casadaban was trying to develop a vaccine to prevent the bacterial infection related to the plague.

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**Symptoms:**
 * Lymph nodes swell causing painful lumps (buboes)
 * Fever, headaches, chills, extreme tiredness and bleeding
 * Some have gastrointestinal symptoms such as nausea and vomiting
 * Pains and aches in the joints may be present
 * Symptoms usually begin within 2 to 6 days after the exposure (bubonic plague)[2]



 **What differentiated the third plague from the previous two plagues?**

 Each pandemic was caused by a different biovar of //Yersinia pestis//. //Y. pestis// is the bacterium responsible for the three different plagues. A biovar is a prokaryotic strain that differs physiologically and/or biochemically from other strains in a particular species. //Y. pestis// is responsible for every plague, the only difference being that they were caused by different forms of the bacterium [3]. //Y. pestis// is a gram-negative bacterium from the family //Enterobacteriaceae//, which is a very large family of bacteria including many familiar pathogens. It can be isolated into the three groups, (1) antique biovar (glycerol fermentation and nitrate reduction), (2) Medievalis biovar (glycerol fermentation and lack of nitrate reduction) and lastly, (3) Orientalis biovar (lack of glycerol of fermentation and nitrate reduction)[4].

 The plague is not only a disease of the past but it is regarded as a re-emerging infectious disease. //Yersinia pestis// is rapidly evolving which recently acquired genes coding for antibiotic resistance [5].

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<span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal; margin-bottom: 0cm;"> **Different forms of //Yersinia pestis// infected plagues:**

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal; margin-bottom: 0cm;"> The least common but most dangerous form of //Y. pestis// is found in pneumonic plague. This plague is due to inhalation of infectious respiratory droplets expelled from a human or animal that has plague pneumonia. It more commonly develops by complications of septicemic plague. This form is characterized by an infection of the lungs. Some signs include<span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal; margin-bottom: 0cm; vertical-align: super;">[6] :
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal;">Severe pneumonia
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal;">High fever
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal;">Difficulty breathing/shortness of breath
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal;">Coughing up blood
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal;">Lack of energy



<span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal; margin-bottom: 0cm;"> Septicemic plague occurs when //Y. pestis// invades and continues to multiply in the bloodstream. This form can develop without detectable lymph node swelling and pain; and characterized by an infection in the bloodstream. Some signs include<span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal; margin-bottom: 0cm; vertical-align: super;">[7] :
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal;">Lack of energy
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal;">High fever
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal;">Shock
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal;">Delirium
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal;">Hypotension

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal; margin-bottom: 0cm;"> The most common disease caused by //Y. pestis// is the bubonic plague. Swollen, painful lymph nodes are caused by the multiplication of bacteria; and characterized by an infection in the lymph nodes. Some signs include<span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal; margin-bottom: 0cm; vertical-align: super;">[8] :
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal;">Fever
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal;">Chills
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal;">Malaise
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal;">Muscle pain
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal;">Nausea
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal;">Sore throat
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal;">Headache
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal;">Extreme weakness
 * <span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal;">Swelling of lymph nodes (buboes)

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal; margin-bottom: 0cm;"> **Transmission:**

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal;"> Transmission commonly occurs when a rodent is infected with the bacterium, and the flea passes along the infection by biting the human host <span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal; margin-bottom: 0cm; vertical-align: super;">[9] <span style="font-family: Arial,Helvetica,sans-serif;">. During the bubonic plague, hygiene was not as important as it is today. Inadequate hygiene standards added to the transmission ability of //Yersinia pestis//. The living condition were a lot more poor between 1894 and 1901 when the third plague pandemic was occurring. These living conditions created more rodents (especially rats) to reside in areas that were heavily populated by humans. Hygiene was the main defense against the bubonic plague.



<span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal; margin-bottom: 0cm;"> **Control and Vaccination:**

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal; margin-bottom: 0cm;"> The progression of the disease is very fast, and the mortality rate is high so diagnosis must be made quickly. There are a few precautions that can be taken to try and avoid contracting the deadly infectious disease<span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal; margin-bottom: 0cm; vertical-align: super;">[1<span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px;">0] <span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px;">. <span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: 17px;">Specific antibiotics can be used to treat the bubonic plague. Such examples include, streptomycin, gentamycin, tetracyclines and chloramphenicol. For someone with severe symptoms the antibiotics are given through intravenous (IV) line. The antibiotics can be taken orally for someone with more mild symptoms.

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<span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal;">Please click on the bubonic plague option to play the interactive video

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal; margin-bottom: 0cm;"> **Germ Theory:**



<span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal; margin-bottom: 0cm;"> Louis Pasteur (1822-1895) is one of the best known nineteenth-century scientists and is considered the founder of microbiology. His most important work would be the discovery of pasteurization of foods – in particular sterilization of milk<span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal; margin-bottom: 0cm; vertical-align: super;">[11]. He had discovered that spoiled organisms could be inactivated in wine by heating it up to a temperature below its own boiling point. This process was then applied to milk and is still extremely important.

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<span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: 18px; margin-bottom: 0cm;"> Some of his other work included the development of vaccines, and solved the mysteries of rabies, anthrax, chicken cholera, and silkworm diseases<span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: 18px; margin-bottom: 0cm; vertical-align: super;">[12]. He helped make the important changes in hospital practices to minimize the spread of disease by microbes. This was possible through his discovery that weakened forms of microbes could be used as an immunization against more powerful forms of the microbe. Pasteur also found that rabies was transmitted by agents so small they could not be seen under a microscope, thus revealing the world of viruses<span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: 18px; margin-bottom: 0cm; vertical-align: super;">[13].

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal; margin-bottom: 0cm;"> **Global Effects:**

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal; margin-bottom: 0cm;"> The plague remains endemic in natural populations of rodents and a medical threat with a number of cases found in humans per year throughout Asia, parts of Africa, the United States and South America. //Yersinia pestis// is common in natural populations of great gerbils in Central Asia, where the human plague is still regularly reported. It has been shown that //Y. pestis// prevalence in gerbils increase with warmer springs and wetter summers based on field data from 1949-1995. It has been indicated that an increase of 1 ⁰ C in the spring can lead to an increase of prevalence by more than 50%<span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal; margin-bottom: 0cm; vertical-align: super;">[14].



<span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal; margin-bottom: 0cm; vertical-align: super;">[1] Health Promotion and Education. "Plague Facts." // NetFORUM Team/Pro //. Web. <http://www.dhpe.org/infect/plague.html>. <span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px; line-height: normal; margin-bottom: 0cm; vertical-align: super;">[2] // Ibid. // <span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px;"> [3] Scott, Susan, and Christopher J. Duncan. "Biology of Plagues: Evidence from Historical Populations.” //The University of Cambridge.// 614.4 (2001): 1-29. Web. <span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px;"> [4] Perry RD, Fetherston JD. Yersinia pestis--etiologic agent of plague. Clin Microbiol Rev. 1997 Jan;10:35-66. <span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px;"> [5] Scott, Susan, and Christopher J. Duncan. "Biology of Plagues: Evidence from Historical Populations.” //The University of Cambridge.// 614.4 (2001): 1-29. Web. <span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px;"> [6] Viruses, Bacteria, Fungi. "Yersinia Pestis » Gram-Negative Bacteria » Pathogen Profile Dictionary. "//Pathogen Profile Dictionary//. Web. <http://www.ppdictionary.com/bacteria/gnbac/pestis.htm> <span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px;"> [7] //Ibid.// <span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px;"> [8] //Ibid.// <span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px;"> [9] //Ibid.// <span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px;"> [10] //Ibid.// <span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px;"> [11] Medical Discoveries. "Pasteur, Louis - Used, Body, Function, Early Life and Research, Germ Theory and Pasteurization, Immunization." // Medical Discoveries //. Web. <http://www.discoveriesinmedicine.com/General-Information-and-Biographies/Pasteur-Louis.html>. <span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px;"> [12] National Health Museum. "Louis Pasteur (1822-1895)." // Access Excellence @ the National Health Museum // .Web. <http://www.accessexcellence.org/RC/AB/BC/Louis_Pasteur.php>. <span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px;"> [13] Medical Discoveries. "Pasteur, Louis - Used, Body, Function, Early Life and Research, Germ Theory and Pasteurization, Immunization." // Medical Discoveries //. Web. <http://www.discoveriesinmedicine.com/General-Information-and-Biographies/Pasteur-Louis.html>. <span style="font-family: Arial,Helvetica,sans-serif; font-size: 12px;"> [14] Stenseth, N. Chr. "Plague Dynamics Are Driven by Climate Variation." //Proceedings of the National Academy of Sciences// 103.35 (2006): 13110-3115. Print.