Yersinia Pestis. A Brief Overview on its History and Biology

Yersinia pestis

Throughout history, mankind and diseases have coexisted, sometimes maintaining a delicate balance, and other times waging full out war upon each other. Some diseases only cause mild discomfort, like the many strains of the virus that causes the common cold, to the bacteria that lives inside of us that can potentially make us deathly ill, such as Escherichia coli, better known as E. coli.

Surviving and thriving with diseases become an integral part of life and living, even though this has also caused many history-changing moments as man has had to learn that, no matter how strong humanity thinks it is, there are things out there that he must bow to. One such disease was one that came in three different surges, decimating the world as it was then, shaping cultures and folklore, as well as beginning the move toward trying to identify what these invisible soldiers are and how to protect from all the malevolent ‘germs’. This disease is formally known asYersinia pestis, but most know it by its more common name, the Bubonic Plague, the Black Death, or the Black Plague.

One of the worst diseases to hit humanity was not something that comes from water, or even the air. This microorganism came directly from infected rats, gaining infectivity as it moved from rat to flea, from flea to human (Waterman). Y. pestisis unique for its origins, as it is one of the only major bacterium that does not depend on human beings as hosts for any gains, and, when ‘processed’ in just the right way, can become the initial ground for one of the most sinister bacterium to ever be introduced to mammals (Tucker).

Y. pestis, when looking at the organism through a microscope, is a rod-shaped bacterium. One of the most important aspects of the bacterium is that it has been documented to grow the best around 82 degrees Fahrenheit, but can survive and thrive in temperatures up to 104 degrees Fahrenheit (Perry and Fetherston). This, of course, means that this bacterium will find the human bodies temperature to be an optimal breeding ground. This would also mean that an infected person would have to have an uncomfortably high fever for it to begin killing of any bacterium that is within the body, and even then, the 104-degree temperature is only on the uncomfortable edge for the microorganism itself.

Infected rat blood, when ingested by fleas, is processed as any other blood meal, working through the digestive system inside of the abdomen of the flea. However, as the infection takes hold, the bacterium slowly grows into a large mass inside of the parasite. This blockage is made entirely of the bacterium. This mass begins to wreak havoc on the flea’s ability to consume blood, resulting in the flea’s inability to gain nutrients from its blood meals. This is an interesting attribute toY. pestis, as the infection causes the flea to slowly starve to death. The flea begins to feed more often in a feeble attempt to survive, subsequently passing the disease on to those it feeds on at an even higher rate (Hinnebusch).

The transmission of the disease is also very interesting, as while it is found in various species of rats, it only begins to spread outside of the rat colonies once the fleas begin to move on to various other hosts. Rats have been found to work best as both vectors of the disease, as well as being the easiest to study, as they are easily containable in specific environments, and fleas are possibly the number one creature to feed upon the rat subjects. Studies have shown that there are over 1,500 species of fleas that can be possible vectors of the disease, but two have been instrumental to research for their ease in studies and the fact they are some of the most commonly found (Perry and Fetherston). These two areOropsylla montana, a flea that primarily effects Ground Squirrels, andXenopsylla cheopis,that feeds off the Oriental Rat. X. cheopisis the species of flea that is commonly associated withY. pestis(Hinnebusch).

The differences between these two different flea species are what make them so susceptible for being the optimal carriers of the disease. Studies show thatO. montana,once it succumbs to infection, is remarkably more infective during the first few days after contact with the bacterium, but it fades rather rapidly until the parasite either clears the bacterium or succumbs to it. X. cheopis,on the other hand, holds a pattern that is the exact opposite. As the infection rages within the parasite, the infectivity increases.

Studies have also shown thatO. montanahas an enlarged esophagus in comparison toX. cheopis, possibly allowing more of the bacterium to pass from the infected flea into the host. Infected fleas of both species were documents as having esophagus enlargement in both blocked and unblocked fleas (Hinnebusch).

Fleas play a major role in the spreading of the bacteriumYersinia pestis, transmitting it from rats and other rodents and vermin to other members of the mammal kingdom. Since fleas are hard to get rid of and are extremely mobile, it does not take long for them to pass on their diseases to human beings. The Bubonic Plague is one such disease that wreaked havoc on man for many centuries, reoccurring in the same areas multiple times over a substantial amount of time. Y. pestisis possibly one of the most ruthless bacterial infections, killing almost everything and everyone in a small amount of time, including the fleas that carry it from host to host.

One such disease came in three different surges, decimating the foundations of the known world as it was, shaping cultures and folklore, and kick-starting the move for humanity to begin the long trek to discover the nature of disease and the malevolent organisms that caused them. This disease is formally known asYersinia pestis,but most of the world knows it as The Black Plague, something that many people do not realize still effects humans to this day.

Yersinia pestishas been around for a very long time. Many believe that the disease had been lurking in Asia for centuries before the major outbreaks occurred. It is not a completely proven fact, but most historians believe that the Black Plague first came to Europe in the years sometime before 700 AD. It is widely believed that up to 40% of Constantinople's population was decimated in this time, but records are scarce (Ray). Due to the lack of found records, it is impossible to say how many lost their lives, or the precise details behind the causes of the outbreak. What brought it, and how quickly it filtered through the population remains a mystery.

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