Yersinia pestis
Drew Menke

Yersinia pestis, is better known as the black plague/bubonic plague (Medievalis) has been the suspected culprit of many epidemics though out the world but most famously is that that killed roughly one third of the Europeans population from 1347 to 1353. (SIX YEARS >25 milion)! Other notable outbreaks or suspected outbreaks include the plague of Justinian (Antiqua) and the third pandemic (Orientalis).  All three of these are suspected biological variants with many different strains isolated from the same time period that differ in either biochemical or physiological makeup. There has not however been a major outbreak in North America or Europe in more than century only isolated cases. Worldwide 1000-3000 cases occur a year.


Yersinia pestis’s is classified as a coccobacillus (rod-shaped) facultative anaerobe that stains gram negative, and produces energy though fermentation. It was first discovered in 1894 by Alexandre Yersin a Swiss/French physician and bacteriology from the Pasteur institute, during an epidemic in Hong Kong.  Yersin was the first to demonstrate Kochs postulate with Yersinia pestis and demonstrate that it was the causative agent in the Hong Kong outbreak.

Yersinia pestis’s preferred or likely method of infection is thought a flee bite and is facilitated in its movement though the world in flees on warm blooded animals, most prominently rodents. Its most prominent symptoms include general malaise, high fever, pain or tenderness to the lymph node region, septicemia (blood poisoning) DIC (disseminated intravascular coagulation or pathological activation of blood clotting), convulsions, shock and dis-colorization of the skin often turning it blackish from necrotizing pneumonia which spawned the term “black death”. It most commonly diagnosed and transmitted in two forms the bubonic plague and pneumonic plague.

Bubonic plagues symptoms become apparent within the week of being infected from a flea bite. Yersinia pestis first targets the lymph nodes where it replicates and produces the characteristic Bubo (swollen, painful lymph nodes) it then spreads and death without treatment occurs for around 90% of those infected but can occur in instances closer to 100%. Pneumonic plague is most prevalent in highly populated centers because of its means of infection which are, contaminated respiratory droplets coughed up and inhaled by another person. This form of infection typically requires a smaller incubation period and has a much greater mortality rate of near or at 100%. With treatment after the initial onset of symptoms roughly 50% of those infected will survive. If either is caught early only 5-20% will be killed, this is why it is so important to treat right away. In the United States and other countries around the world infected patients with Yersinia pestis must be isolated.

Yersinia pestis’s such high mortality rate is believed to be due to it causing septicemia-induced shock. Host defense or resistance to Yersinia pestis’s deadly effects requires the acquisition or possession of the opsonic antibodies against F1 and V antigens, antibodies against F1 and V antigens induce phagocytosis and neutrophils. A vaccine for Yersinia pestis was introduced into the United states market but produced high rates of the vaccinated acquiring the bubonic plague, it was subsequently pulled from the market by the FDA. There have been other attempts at vaccines but none to date that provide protection at a reasonable cost or risk. Descendants of survivors of the medieval epidemic have been seen to be more resistant and less likely to acquiring an infection from Yersinia pestis to date.

Infected patients today are treatment from a choice and/or combination of antibiotics like Streptomycin, chloramphenicol tetracycline and fluoroquinolones (synthetic). If this method of treatment is insufficient circulatory, ventilator, or renal support is used. Yersinia pestis for a number of years has been suspected to have a potential in biological warfare because of its ability to be transmitted though the air and high mortality rate in urban and highly populated areas. It is thought that it could be easily spread by aerosol as well as other means.

I however like to look at it as a plush black stuffed coccobacillus with buggy eyes. CUTE!!

It I made a mistake please correct me!!



*Disclaimer - This report was written by a student participaring in a microbiology course at the Missouri University of Science and Technology. The accuracy of the contents of this report is not guaranteed and it is recommended that you seek additional sources of information to verify the contents.


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