Yersinia pestis a.k.a. Black Plague a.k.a. Black Death

Yersinia pestis

Yersinia pestis, Black Plague, Black Death.

Yersinia pestis (formerly Pasteurella pestis) is a Gram-negative, rod-shaped coccobacillus, a facultative anaerobic bacterium that can infect humans and animals. It causes the deadly disease named plague. Human Y. pestis infection takes three main forms: pneumonic, septicemic, and bubonic plagues. All three forms were responsible for a number of high-mortality epidemics throughout human history, including: the sixth century’s Plague of Justinian; the Black Death, which accounted for the death of at least one-third of the European population between 1347 and 1353; and the 19th century’s Third Pandemic. These plagues probably originated in rodent populations in Europe or much less likely China.

Y. pestis was discovered in 1894 by Alexandre Yersin, a Swiss/French physician and bacteriologist from the Pasteur Institute, during an epidemic of plague in Hong Kong. Yersin was a member of the Pasteur school of thought. Kitasato Shibasaburō, a German-trained Japanese bacteriologist who practiced Koch’s methodology, was also engaged at the time in finding the causative agent of plague. However, Yersin actually linked plague with Y. pestis. Originally named Pasteurella pestis, the organism was renamed in 1967.


During the past few days, I’ve posted beautiful pictures of MERS and ebola viruses attacking monkey cells. This picture is of Yersinia pestis bacteria in the gut of an infected flea.

Y. pestis has been far deadlier than either of the two viruses, but probably only because it’s been around longer and attacked before the advent of modern science or medicine. During a six-year period between 1347 and 1353, it wiped out a third of the population of Europe. Such an outbreak now would be relatively minor, since it’s susceptible to treatment with antibiotics. Viruses, unfortunately, are not.

Live plague bacteria; dead MERS and ebola viruses

Keep in mind that bacteria are live single-celled organisms, whereas viruses are just dead chemicals. Nevertheless, they both reproduce inside appropriate hosts and sometimes cause disease and death. Viruses can do this because they contain genes corresponding vaguely to some of the genes in living organisms. When they enter a living cell, their host’s machinery copies them along with its own DNA. By blindly and unintentionally taking advantage of the cell’s reproductive processes, they reproduce themselves like exceedingly tiny little chemical zombies and even evolve into new forms, just as if they were living creatures. But they are not.

Certain bacteria, like Y. Pestis, also grow mainly inside a host, but for a different set of reasons. That’s where it gets the best combination of nutrients it requires, as well as precise environmental needs like moisture, temperature, protection from the elements, and maybe a thousand other little things. But bacteria are real living creatures many times larger than most viruses, and they have the ability to engulf nutrients, make use of oxygen as we do (in most cases), and make their own proteins and genetic materials without hijacking the host’s chemical factories to do it.

As seen from the Wikipedia quote above, Y. pestis has been a deadly enemy of mankind for at least 1,700 years and strikes in at least three forms. It’s not likely to go away soon, either; because it infects a variety of rodents and other small mammals without killing them. Fleas usually transfer it to humans, although the pneumonic form spreads through coughing and sneezing once somebody gets it.

Ring around the rosie.

The popular children’s game “Ring Around the Rosie” may have originated during one of the ancient epidemics, although some experts disagree about this. English versions include references to sneezing and falling down, as well as “pockets full of posies.” It is said that sneezing was a symptom of the disease, while falling down refers to dying. A “pocket full of posies” was to ward off the smell of death. The “rosie” in the title may have been a rose bush.

Ashes to ashes, we all fall down.

Similar games, using similar tunes and similar lyrics, appear in several other European languages; but experts don’t agree on their sources. The game seems pretty morbid, if that really is what the words refer to; but I suppose a little bit of morbidity is to be expected when it seems as if everybody you know is dying.



Please leave a comment. Tell me what you like or dislike about this post, but please be polite about it. Remember, this site is all "G Rated." Thank you.

This site uses Akismet to reduce spam. Learn how your comment data is processed.