The Black Death took place from 1347 up to 1353 and ended up ravaging Europe and leaving millions dead. Outbreaks of the plague carried on across Europe until the start of the 1900s.
About Black Death
Live Science notes how it is commonly recited that rats were the culprits behind the spread of the plague. In some areas of the world, the bacterium behind the plague, Yersinia pestis, stays within wild rodents as well as their fleas. Such a thing is dubbed an animal reservoir.
Though the plague outbreak starts among rodents, , at times it reaches humans as well. While Europe could have had animal reservoirs that led to plague pandemics, the said plague could have been reintroduced again and again from Asia.
A recent study included in the PNAS journal revealed that environmental conditions across Europe would have stopped the plague from lasting in long-term and persistent animal reservoirs. Given this, specialists are left with a question regarding how the Black Death was able to thrive across Europe for such a remarkable duration.
How Did Black Death Persist?
According to the Conversation, there are two possibilities granted by the study. Firstly, the plague could have been reintroduced from reservoirs in Asia. Secondly, there may have been medium-term or short-term reservoirs across Europe. Both scenarios could have also supported each other.
However, the Black Death's fast transmission and succeeding outbreaks in the next centuries suggest that rats could not have been the culprits behind the plague's transmission.
To know if the plague could persist in long-term reservoirs across Europe, the scientists assessed factors like climatic conditions, soil qualities, rodent varieties, and terrain types. All of these seemingly affected the plague's capacity to persist within reservoirs.
The Conversation reports that, for instance, higher concentration levels of certain soil elements, such as iron, copper, and magnesium, high pH of the soil, lower temperatures, lower rainfall, and higher altitudes seem to support the development of reservoirs that are persistent. The reason behind this, however, is not quite clear.
Based on the scientists' analysis, it was seen that plague reservoirs of wild rodents for centuries were less likely to have existed since the start of the Black Death until the early 1900s. In-depth research does not cross out any of the said reservoirs across Europe.
Such a case sharply differs from regions within the western US and China, which are areas that harbor all of the aforementioned conditions for the persistent wild rodent reservoirs of Yersinia pestis.
Are Rats Really the Culprit Behind the Plague?
To learn more about how rats played a role in the spread of the plague, the researchers looked into three pandemics and compared them.
The Conversation notes that contemporary specialists describe the second pandemic plague as having a faster and wider spread compared to any other disease of the Middle Ages. Irrespective of how the second pandemic started, rodents that were wild and not wild (particularly rats) had slower movement compared to the spread across the continent.
Other than this, there were also discrepancies regarding the plague's seasonality. Third pandemic plagues closely mirror rat flea fertility cycles. These intensify in humid circumstances and within a temperature range of 10 to 25 degrees Celsius.
However, the plagues of the second pandemic plagues were able to cross the winter season bubonically. Other than this, across the climes of the Mediterranean, the plague from 1348 up to the 1500s peaked during the driest and hottest months.
Such observations do not coincide with plague seasons across such regions in the 2000s. Due to higher temperatures and comparatively lower humidity, such months were the least likely times for rat or human outbreaks to take place.
Such differences make specialists wonder if the plague's bubonic form was dependent on rodents for transmission when it may have efficiently spread from human to human instead. Questions regarding the exact roles of rats and humans in these previous pandemics require further study.
Read also: Black Death Vaccine: First Phase of Human Trials Begins, Will This End the Bubonic Plague?
Check out more news and information on the Black Death in Science Times.
