La Peste (1695) wax sculpture, Gaetano Zumbo, Museum of Specola, Florence

The Black Death: the Plague that Sowed Terror and Death in Medieval Europe - Part 2

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Science had to wait until the nineteenth century to banish the idea of ​​a supposed supernatural origin of the plague. The fear of a pandemic on a global scale persisted for four centuries (and even longer) after finding that the disease had spread out over vast regions of Asia as well.

The Deadly Bacteria behind the Bubonic Plague

However, that same fear propelled scientists to search for the origins of the plague. Two bacteriologists, Kitasato and Yersin, independently (but practically in unison) discovered in 1894 that the real cause of the plague was the bacteria Yersinia pestis (named in honor of Yersin.)

Yersinia pestis was present in black rats and other rodents and is thought to have been transmitted by parasites living in/on these animals, especially fleas. The plague was, therefore, a zoonosis disease passing from animals to humans. Zoonosis helps to explain why the spread of the plague was so rapid and easy, because rats and humans lived alongside each other and shared barns, mills, roads, and housing, in addition to being transported together in boats. 

Portrait of Alexandre Emile John Yersin, Swiss physician and bacteriologist, co-discoverer of the bacteria responsible for the bubonic plague

Portrait of Alexandre Emile John Yersin, Swiss physician and bacteriologist, co-discoverer of the bacteria responsible for the bubonic plague. (Wikimedia Commons )

Both bacteriologists discovered that the bacteria were present in homes for a period of between 16 and 23 days before the first symptoms of the disease took hold in the victims. Then three to five more days passed until the first deaths occurred. On average, it took another week until the population acquired full awareness of the seriousness of the problem they were facing.

A Medieval Society without Cats

Remember that when the plague struck Europe, the continent was undergoing a deep economic crisis caused by the decline of the feudal system due to a series of bad harvests and excessive overcrowding.

In medieval Europe one of the main predators of the black rat was the cat, domesticated by the ancient Egyptians and introduced on the continent by the Phoenicians in the ninth century BC. Since then cats lived with humans and served a role by keeping away rats and other rodents. But everything changed in the twelfth century AD.

Cats - above all black cats, were exterminated in many regions of Europe because they were considered animals linked to witchcraft and demonic practices during the middle ages.

Cats - above all black cats, were exterminated in many regions of Europe because they were considered animals linked to witchcraft and demonic practices during the middle ages. (Torange)

In the late twelfth century in southern France there was the "First Inquisition" which was created by religious courts to combat heresy and witchcraft. At the same time cats began to be considered suspicious animals because of their independent nature and their ability to survive in extraordinary circumstances. Gradually they began to be associated with witches and witchcraft. The population began to fear cats as they associated them with satanic and demonic characteristics.

The first step to condemn the “evil” black cats was given by Pope Gregory IX, who in his Bull “Vox in Rama,” in the early thirteenth century, stated that  “The evil black cat had fallen from the clouds bringing unhappiness to man.” That was how medieval citizens began to believe that it was safer to exterminate cats – especially the black ones.

However, the various superstitions and ecclesiastical decisions meant that with the passage of time, there was an almost widespread killing of cats in many parts of Europe. Several sources indicate the number of cats killed was approximately 200,000. The result of this extermination was the rapid proliferation of rodents, particularly the "black rat" which, as we saw above, was found out to be the main transmitter of the deadly Black Plague.

Plagues: Types, Symptoms and Consequences

A plague is a severe and often deadly bacterial infection caused by the bacterium Yersinia pestis. Rodents usually carry the disease and it spreads through their fleas. People contract it when they were bitten by a flea that carries the bacteria from an infected rodent. In exceptional cases, the disease can also be contracted by handling an infected animal.

Bacteria Yersinia pestis

Bacteria Yersinia pestis (Public Domain)

A plague infection of the lungs, called pneumonic plague, can spread from one human to another, when someone with pneumonic plague coughs and microscopic droplets carrying the bacteria move through the air and are inhaled by another person. 

The plague can happen almost anywhere. Some scholars believe there is still a moderate possibility of a plague occurring in Africa, Asia, and South America. Recently there have even been cases of a plague in the United States. 

The average time between infection and the onset of symptoms is around 2 to 8 days, but in the case of pneumonic plague it may be only one day. The three most common forms of plague are bubonic plague, pneumonic plague, and septicemic plague.

Bubonic plague is an infection of the lymph nodes. Its symptoms usually appear suddenly, after 2-5 days of exposure to the bacteria. Its main symptoms include chills, fever, malaise, headache, muscle pain, seizures, and formation of bubones (painful swollen lymph nodes), armpit or neck.

Pneumonic plague is a lung infection and its symptoms also appear suddenly, normally within 2 to 3 days after exposure. Symptoms of the pneumonic plague include severe coughing, difficulty breathing, coughing or expulsion of blood and/or bloody/foamy mucus, and chest pain when breathing deeply.

The formation of buboes is one of the main symptoms of bubonic plague. Illustration Toggenburg Bible (1411)

The formation of buboes is one of the main symptoms of bubonic plague. Illustration Toggenburg Bible (1411) (Wikimedia Commons)

Septicemic plague, which is an infection of the blood, can cause death even before showing symptoms. If symptoms do occur they often include abdominal pain, bleeding due to problems with blood clotting, diarrhea, fever, nausea, and vomiting.

People infected with the plague need immediate treatment. If it is not received within 24 hours of the onset of initial symptoms, the victim of the disease will likely die. To fight the disease, antibiotics such as streptomycin, gentamicin, doxycycline or ciprofloxacin are used today. The use of oxygen, intravenous fluids, and respiratory support is often also necessary.

In addition, patients suffering from pneumonic plague must be isolated from caregivers and other patients. Also, people who have had contact with someone infected with pneumonic plague must be monitored closely and receive antibiotics as a preventive measure.

What if it wasn’t Black Rats?

According to the findings of a new study by Nils Stenseth, a researcher at the University of Oslo, we may have to rewrite part of the story of the Plague because black rats may not be to blame for the outbreak of the bubonic plague in Europe after all.

According to the research team in charge of the study, repeated plague epidemics were caused by another rodent: the gerbilino or gerbil (Gerbillinae) from Asia.

A Mongolian gerbil, perhaps the true flea-bearers that caused the plague epidemics in Europe.

A Mongolian gerbil, perhaps the true flea-bearers that caused the plague epidemics in Europe. (Wikimedia Commons)

After comparing the tree rings in Europe where the worst outbreaks of the plague took place, it was noted that the weather conditions were not optimal for rats to be the culprits. The team wrote in their report:

“We showed that there were good conditions for gerbils and fleas in Central Asia, and the bacteria appeared a few years later in European port cities and then expanded across the continent. For that warm summers were needed, without much rainfall - dry but not too dry. We looked at the broad spectrum of climatic indices and saw no relationship between the onset of fever and climate.”

The team believes that the specific weather conditions in Asia may have caused the increase in the gerbil population, what they claim were the real transmitters of the disease.

Burned houses in China during the plague of 1890.

Burned houses in China during the plague of 1890. (Wikimedia Commons)

Stenseth’s team now plans to analyze the DNA of the plague bacteria obtained from former European skeletons. If the genetic material shows a lot of variations, it may indicate that the theory is correct because it would suggest different waves of Plague arrivals from Asia - showing more than a single strain which is thought to arise from one main rat invasion.

The plague disappeared from Europe in the nineteenth century. However, even today, cases are still recorded around the world.

Featured image: La Peste (1695) wax sculpture, Gaetano Zumbo, Museum of Specola, Florence (Wikimedia Commons)

Author: Mariló TA

This article was first published in Spanish at and has been translated with permission.


California investigates possible second case of plague visited Yosemite. Artículo/19-08-2015.

The Black Death, the epidemic more mortífera.

What caused the Black Death in Europe?

Medical Encyclopedia. Death.

Stories of our history. The Black Death.

Causes and consequences of the plague negra

Cats, witches and black plague.

Ole J. Benedictow. (2011). The Black Death, 1346-1353: The Complete History.

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