Y is for Yersinia Pestis

Y is for Yersinia Pestis

Salem Friendship (Photo credit: Josh McGinn)

Salem Friendship (Photo credit: Josh McGinn)

Fall 1347 – I begged my parents to allow me to bring the harvest to town today. I have always loved watching the ships come into harbor and see the wares offloaded. The fabrics and fruits from The East ensnaring my attention, even though I know I will never have them. I visualize the colors dancing before my eyes. I watch the flags wave in the wind and the rats scurry down the hold lines. I hear the calls from the sailors to the shore, there is a flurry of activity and shouting. I don’t have time to investigate, I need to sell what I can and get home before nightfall.

As I return home with an empty cart, I mindless scratch at my ankles and legs, picking off the fleas and crushing them. Today’s produce sales were good. My parents will be proud. For the next two days, my parents allow me to bring the produce to town, but on the third day, I can barely walk. My mother applies poultices to my ankles and legs where the skin is torn and bleeding. There are swellings in my groin and armpits that stretch the skin painfully, finally bursting to drain pus and blood. Despite extra blankets and laying near the hearth, I shake from chills and fevers. The cough begins a few days later. I look down, I am covered in blood. As I lean back into my blankets, I smell smoke in the air.

†  †  †

Yersinia pestis model at the Smithsonian Natural History Museum (photo credit: Tim Evanson)

Yersinia pestis model at the Smithsonian Natural History Museum (photo credit: Tim Evanson)

Yersinia pestis, a gram negative rod-shaped coccobacillus, is the bacteria responsible for The Plague. In October 1347, 12 ships arrived in a Sicilian port, the crews were dead or dying, despite the attempts to turn them away, it was too late. The Black Death had arrived. The rats that traveled on merchant ships from Asia began to die off as well. The fleas that infested them needed a new source of food, so they began to feed off of humans. In the process, the fleas transmitted Yersinia pestis when they would vomit the rat’s blood into their human victim. The bacteria replicated at the site of flea bites and then spread through the lymphatic vessels, causing lymph nodes to swell (buboes) before erupting. Sometimes, the bacteria would cause sepsis (a severe blood infection) or spread to the lungs. These are the three forms of Plague: Bubonic, Septicemic, and Pneumonic.

From 1347 to 1353, one-third of Europe’s population died from “The Black Death” (the name given to this second Yersinia pestis pandemic). There was no escape from The Black Death in Europe. The cities were full of death, people would flea to the countryside, but the fleas followed infecting people and animals. Entire towns died off. In an attempt to prevent spread of disease and because there were few to bury the remains, homes and bodies were burned.

Today, although outbreaks still occur, Yersinia pestis can be treated with antibiotics.

Yersinia pestis found in a liver - note yellow spots (Photo credit: Jennifer Stewart, DVM)

Yersinia pestis found in a liver – note yellow spots (Photo credit: Jennifer Stewart, DVM)

Animals are also at risk, although cats are more prone to having and spreading infection compared to dogs.

Prevention is the best protection though.

  • Be aware if you live in an endemic area
  • In endemic areas, keep dogs and cats protected with flea prevention medications year round
  • In endemic area, do not allow dogs and cats to sleep in bed with you
  • Decrease rodent populations around homes, barns, businesses, and recreation areas
  • Use insect repellents when in areas that fleas are common
  • Wear gloves and other appropriate gear when handling animals or specimens that may be infected with Yersinia pestis


Photo Credit:

Yersinia Pestis Model at Smithsonian Museum of Natural History by Tim Evanson http://www.flickr.com/photos/23165290@N00/7283938624/ via Photopin.com http://photopin.com with Creative Common License https://creativecommons.org/licenses/by-sa/2.0/

Ship Josh McGinn http://www.flickr.com/photos/svenstorm/1548728822/ via Photopin.com http://photpin.com with Creative Common License https://creativecommons.org/licenses/by-nd/2.0/

Yersinia pestis in a liver by Jennifer Stewart, BS, DVM, DAVCP, MRCVS


4 thoughts on “Y is for Yersinia Pestis

    • Yes, it can be devastating. Thankful, now it is significantly easier to treat. The pandemics in the past were able to do so because there no antibiotics to treat them. It is amazing what science and medicine can give us.


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