Plague rats were not the carriers

Experts are studying how the plague spread so much in the Middle Ages

In the 14th century, the plague reached Europe, causing people to die in parts of the country. The plague is arguably one of the worst pandemics in human history, claiming millions of lives. The cause of the disease is now known, but it was still unclear how the plague could spread so quickly from person to person. Researchers now found that primarily lice and human fleas were responsible for the rapid spread and not, as previously thought, rats and their parasites.

The scientists of the University of Oslo found in their study that the plague in the Middle Ages was probably transmitted via lice and fleas from person to person. So far, there have been assumptions that the disease was spread by rats and their parasites. The experts published the results of their study in the English-language journal Proceedings of the National Academy of Sciences..

Due to the high risk of infection, many plague doctors protected themselves with masks with long bills and sealed eye openings. (Image: Dennis van de Hoef / fotolia.com)

The plague and its effects in the Middle Ages

The plague is a terrible disease, which alone in the period between the year 1346 and 1353 nearly one third of the population in Europe was ravaging. In outbreaks, which occurred again and again for about 500 years, up to 60 percent of the population succumbed to the bacterium Yersinia pestis. The disease is also known as black death thanks to its most famous outbreak, due to blackened and swollen lymph nodes. These occurred after bacteria had penetrated through the skin.

Human fleas and lice were the transmitter

The biggest mystery of the disease is the physical mechanism that hastened the rapid spread of the disease, say the experts. In a long-standing theory, rats, mice or other rodents acted as hosts of the bacteria. For a long time, fleas were considered to be the main carriers of the infected animals and then humans. The rapid pace of transmission and spread can be explained but rather by human fleas and lice, explain the researchers. Such parasites were very widespread in the Middle Ages and virtually omnipresent.

Rats probably did not play a big role in the spread

According to the researchers, the deadly bacterium transmitted from a rodent to humans and parasites sometime before the big outbreak of the plague. So it could spread more and more. The rats probably did not play a big role anymore. The plague can be treated with antibiotics if it is detected early, but the symptoms can be fatal if not treated in time. However, in the Middle Ages such drugs were not available to those affected. The newly developed mathematical model used in the study revealed that rodents were unjustly accused of spreading the plague, according to author Katharine Dean of the University of Oslo.

Scientists create model for the spread of the plague

The scientists created a list of plague characteristics based on current field observations, experimental data, and estimates for their model. For example, these included facts that the likelihood of recovering from the disease was 40 percent, and a louse with pest bacteria remained infectious for about three days. One person during this time could house on average about six fleas. So-called mortality records from several centuries provided the most critical detail. At that time, observers were able to document the increase and decrease in plague deaths per week because the disease was so virulent and the signs of infection were so obvious, explains Boris Schmid of the University of Oslo.

There were three different scenarios for the model

By analyzing three different scenarios, the scientists were able to determine how the plague spread. In a common lice and fleas the plague. In the second scenario, rodents and their parasites spread the plague. In the third case, coughing people spread a version of the disease called pulmonary plague.

What did the model do??

The model with the rodents did not correspond to the historical mortality rates. The result showed a delayed, very high increase in deaths, which is not reflected in the mortality data. Also, the model with the lung plague did not fit the data of the former deaths, say the experts. Human body lice or fleas were the main transmission pathways in medieval pandemics, the authors speculate. Earlier, researchers had expressed some doubts about the theory that the fleas of rats (Xenopsylla cheopis) have triggered the spread of the plague.

Even today, there are still outbreaks of the plague

Plague outbreaks are still taking place today. According to the World Health Organization WHO, the disease has recently been suspected or confirmed in 171 deaths in Madagascar. (As)