2History of PlagueArguably the ultimate scourge of mankind (and over 100 species of animals) was the so-called Black Death. The generic "plague" (with a lower case p) has entered the language as a descriptor for any deadly epidemic disease. Plague (with an upper case P) is caused by Yersinia pestis, a rod-shaped, Gram negative bacterium. As few as one bacterium is an infective dose!
3FactsPlague is caused by the bacteria Yersinia pestis. Rodents, such as rats, carry the disease. It is spread by their fleas. People can get the plague when they are bitten by a flea that carries the plague bacteria from an infected rodent. A plague lung infection called pneumonic plague can spread from human to human. An epidemic may be started this way.In the Middle Ages in Europe, massive plague epidemics killed millions of people. Plague can still be found in Africa, Asia, and South America. Today, plague is rare in the United States, but it has been known to occur in parts of California, Arizona, Colorado, and New Mexico.
4FactsThere three most common forms of plague are: Bubonic plague -- an infection of the lymph nodes Pneumonic plague -- an infection of the lungs Septicemic plague -- an infection of the bloodThe time between being infected and developing symptoms is typically 2 to 7 days, but may be as short as 1 day for pneumonic plague. Risk factors for plague include a recent flea bite and exposure to rodents, especially rabbits, squirrels, or prairie dogs, or scratches or bites from infected domestic cats.
5History of PlagueSimple children's rhymes illustrate some profundities associated with the times, e.g. ”Ring around the rosies, A pocket full of posies, Ashes, ashes! We all fall down.”
6The Black DeathAlso known as the Great Plague originated in China in 1334 and spread along the great trade routes to Constantinople and then to Europe, where it claimed an estimated 60% of the European population. Entire towns were wiped out. It has even been considered a factor in the emergence of the Renaissance in the late 14th century.
7The Black DeathIt is estimated that The Black Death was responsible for 200 million deaths in Europe between , with outbreaks occurring well into the 1400’sThe 1328 outbreak in China caused the population to drop from 125 million to 90 million in just fifty years 7500 victims of the disease were dying every day
8Case StudyA 25-year-old New Mexico rancher was admitted to an El Paso Hospital on February 12 because of a two-day history of headache, chills, and fever. The day before admission, he began vomiting. The day of admission, an orange-sized swelling in the left axilla was noted. A lymph-node aspirate and a smear of peripheral blood were reported to contain gram-positive cocci, often in pairs. Under the assumption that a gram-positive organism had caused the patient's illness, he was given cefoxitin.
9Case Study cont.The man was acutely ill. Within a few hours of admission, he had a cardiopulmonary arrest. During resuscitation efforts, he vomited and aspirated his vomitus; a chest X-ray showed bilateral infiltrate. Additionally, the patient bled from several body sites. The patient died within 6 hours of admission. In the 2 weeks prior to becoming ill, the patient had trapped, killed, and skinned 3 kit foxes, 4 coyotes, and 1 bobcat. The patient had cut his left hand shortly before skinning the bobcat on February 7
10PathogenesisYersinia pestis is primarily a rodent pathogen, with humans being an accidental host when bitten by an infected rat flea. The flea draws viable Y. pestis organisms into its intestinal tract. These organisms multiply in the flea and block the flea's proventriculus. Some Y. pestis in the flea are then regurgitated when the flea gets its next blood meal thus transferring the infection to a new host. While growing in the flea, Y. pestis loses its capsular layer. Most of the organisms are phagocytosed and killed by the polymorphonuclear leukocytes in the human host. A few bacilli are taken up by tissue macrophages. The macrophages are unable to kill Y. pestis and provide a protected environment for the organisms to synthesize their virulence factors.
11PathogenesisThe organisms then kill the macrophage and are released into the extracellular environment, where they resist phagocytosis by the polymorphs. The Y. pestis quickly spread to the draining lymph nodes, which become hot, swollen, tender, and hemorrhagic. This gives rise to the characteristic black buboes responsible for the name of this disease. Within hours of the initial flea bite, the infection spills out into the bloodstream, leading to involvement of the liver, spleen, and lungs. The patient develops a severe bacterial pneumonia, exhaling large numbers of viable organisms into the air during coughing fits. As the epidemic of bubonic plague develops, it eventually shifts into a predominately pneumonic form, which is far more difficult to control and which has 100 percent mortality.
12TransmissionFlea bites. Plague bacteria are most often transmitted by the bite of an infected flea. Contact with contaminated fluid or tissue. Humans can become infected when handling tissue or body fluids of a plague-infected animal. Infectious droplets. When a person has plague pneumonia, they may cough droplets containing the plague bacteria into air.
14SymptomsBubonic plague symptoms appear suddenly, usually after days of exposure to the bacteria. Symptoms include:ChillsFeverGeneral ill feeling (malaise)HeadacheMuscle painSeizuresSmooth, painful lymph gland swelling called a buboCommonly found in the groin, but may occur in the armpits or neck, most often at the site of the infection (bite or scratch)Pain may occur in the area before the swelling appears
15TreatmentPeople with the plague need immediate treatment. If treatment is not received within 24 hours of when the first symptoms occur, death may occur.Antibiotics such as streptomycin, gentamicin, doxycycline, or ciprofloxacin are used to treat plague. Oxygen, intravenous fluids, and respiratory support usually are also needed.
17This bar graph shows the number of plague cases by year, but can be interpreted in two separate time frames.Plague cases in the United States, 1900–2010. In 1907, an outbreak of plague followed in the aftermath of the San Francisco earthquake. Since the mid–20th century, plague in the United States has typically occurred in the rural West.
18Plague WorldwidePlague epidemics have occurred in Africa, Asia, and South America but most human cases since the 1990s have occurred in Africa.
19SourcesMedicine Plus Hartford University Science Illustrated scienceillustrated.com.au University of Maryland Centers for disease control Middle Ages History A.T. Still University
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