Around the year 1346, the first cases of the Black Death began in Europe, a deadly disease that claimed millions of lives on the old continent. This was not the first epidemic unleashed by the bacterium Yersinia pestis : in the 6th century it had also been responsible for the Justinian plague, which devastated the Byzantine Empire. Nor would it be the last, as in the 19th century it also raged in Asia and today there are still small outbreaks of the disease, which fortunately can already be controlled with antibiotics.
Why was the Black Death epidemic so deadly? A work published in the journal Nature in 2011 revealed the results of an analysis that compared the genomes of different strains of Y. pestis and concluded that there are no genetic differences between the bacteria that caused the plague in medieval Europe and those that cause the plague. at the moment. That is, it is not that they were more virulent, so the reasons why so many lives were claimed are surely of another nature.
This is very easy to understand if we think about the mechanism used by the bacteria that cause the Black Death to spread. Like so many other parasites, Y. pestis uses animal vectors, and in this case rats and fleas are very common. When a flea carrier bites a person, it transmits the bacteria, and this individual becomes infected. The overcrowded and unsanitary conditions in which the cities of Old Europe lived at that time were the perfect breeding ground for fleas to quickly transmit the disease.
Bubonic plague and pneumonic plague
The black plague is also transmitted by other routes: “When an infected individual does not receive adequate treatment, the most probable thing is that the bacteria proliferate and move towards the lungs”, explains David G. Jara in his book The Grasshopper Enchantress and other essays on the natural history of parasites . “Once they have colonized these organs, they will come out along with the coughs and bloody sputum of the patient, and the bite of any insect will no longer be necessary to spread the disease from person to person; All you need to do is breathe in some of the bacteria-laden droplets of saliva to make you sick. This variant is known as pneumonic plague and, in addition to being more lethal than bubonic plague – the one that produces buboes or swollen lymph nodes -, it spreads at full speed among individuals in a population without the participation of rodents or fleas ”.
This is how the plague came to Europe
The most widely accepted hypothesis argues that the plague would have originated in Mongolia : in this country, marmots are a very frequent reservoir of the disease, and it is likely that fleas had caused the jump to man. “It is even possible that the participation of the flea was not even necessary to take this first step, since currently marmot meat is a product consumed by shepherds and hunters of the Mongolian steppes”, explains David G. Jara in the book aforesaid.
The Mongol soldiers displaced to the battle front in the Crimean peninsula would have brought the disease to this region, which in turn was an important starting point for trade routes that reached all of Europe, and in this way Yersinia pestis would have colonized the continent at high speed.
The details of the spread of bubonic plague in Europe are a most interesting topic in the field of epidemiology. Investigations suggest that the ‘ground zero’ in Europe would be the Sicilian port of Messina (Italy), where a ship full of dying sailors from the Black Sea would have arrived in December 1347.
According to a study published in Scientific Report in 2017, the intricate network of roads that connected major European cities during the Middle Ages facilitated the spread of the plague. The work showed, thanks to a mathematical simulation, that the most central cities within the communication network, as well as the most populated, were those with the highest incidence of the Black Death , in which the disease manifested itself with greater severity and also outbreaks were more likely to recur.
The black plague today
What Happens Today? Could the bubonic plague turn into a terrible epidemic again? Currently, sub-Saharan Africa concentrates most of the new cases, which reappear periodically from time to time. One of the possible causes that plague is so difficult to eradicate is due to the fact that, according to a study published in the journal Applied and Environmental Microbiology, the bacterium Y. pestis would use amoebas as a refuge when conditions are unfavorable, and this It would ensure a prolonged survival in time.
