How the Bubonic Plague Spread

The bubonic plague was one of the most notorious diseases of the Middle Ages. Although it was only responsible for a few hundred deaths per year in medieval Europe, it wiped out large swaths of the population. As a result, scientists have spent centuries trying to understand how the plague was transmitted, and why it struck so hard in the fourteenth century.

Early modern medical professionals recognized the plague as a contagion transmitted through the air, which they called the plague or pestilence. The disease appeared after a massive infestation of fleas from an animal bite or a contaminated surface or object. It was very difficult to diagnose early on because the symptoms resembled those of other diseases. In fact, it was only in the middle of the eighteenth century that physician-researchers first noted the similarity between the symptoms of bubonic plague and those of jaundice.

In order to try to determine what actually caused the plague, scientists studied the buboes, or pustules, on the patients’ skin. While these pustules were not harmful to humans, they did emit a pungent odor that could alert the immune system to an upcoming outbreak. For that reason, people were advised to cover their body with protective clothing and bury clothes, blankets, bedding, and other personal items that might be contaminated.

Scientists also concluded that the plague was spread by rodents. This conclusion was drawn from the appearance of rat droppings in the buboes. In addition, the buboes often contained sores, which were interpreted as a wound caused by a rat bite.

When scientists determined that the bubonic plague was transmitted through the air, they believed that mice and rats would jump from house to house in search of food, causing an epidemic. When an outbreak occurred, death was common.

They also determined that while the bubonic plague had originated in Asia, it traveled south to Europe and could travel as far as the Mediterranean Sea. At this time, doctors noticed that the buboes tended to appear in areas where people lived near streets, which led them to conclude that the buboes resulted from “lewd, filthy public places.”

To understand how the plague was spread, doctors also studied the fleas that carried the disease. Fleas feasted on the blood of human victims. Upon emergence of the disease, the fleas had to seek another host.

Scientists concluded that the plague was spread by fleas, which are now widely found in all parts of the world. They also found that although mice and rats were responsible for outbreaks, they sometimes also came into contact with humans and could transfer the disease to them. According to scientists, the fatality rate was forty percent, which can be attributed to “high prevalence of collateral hosts.”

When scientists learned how the plague was spread, they devoted many years to studying the buboes and conducting experiments on mice. One scientist created an experiment to determine whether rats were more likely to bite a mouse with large pustules, while another attempted to pinpoint the source of the plague by injecting rats with a virus that mimicked the plague’s symptoms.

Furthermore, scientists focused on the living conditions in which plague victims lived, including the numbers of people and the amount of cleanliness in the surroundings. They conducted experiments to see if the rats could transmit the disease to humans. In a study published in 1907, it was determined that a rodent strain that had lived in dark, damp tunnels where there were not many people was unable to spread the plague.

In the meantime, it was not possible to treat or cure the bubonic plague on the spot. Although several attempts were made in the nineteenth century, no treatment worked and even after exposure to ultraviolet rays, the symptoms of the disease persisted. As a result, people became fearful of contracting the disease and buried their dead.

In the twentieth century, plague reappeared, and scientists concentrated on studies of the bubonic plague. In addition, a separate group of scientists examined the effects of modern hygiene practices on the bubonic plague, such as the use of sanitary protection. Their research concluded that the bubonic plague was extremely contagious and highly transmissible through coughing, sneezing, running nose, coughing, or inhalation.