The Black Death - World Deadliest Epidemics Pt. I

A couple of weeks ago, we finished our blog post series about One Health and the Sustainable Development Goals in which we covered each SDG and how it relates to One Health. For this new series, we will talk about something different, but equally important. 

Today, we are launching a series of blog posts discussing the deadliest recorded epidemics in history. We think that looking back at what happened in the past could help us all to understand how pandemics and epidemics are managed now, what we have learned from some of the darkest moments in public health history, and how it has helped us prevent potentially bigger pandemics, and more recently, build concepts like One Health. But do not worry, check our social media channels, where we will provide you with some memes to make the whole experience a bit more fun.

A plague doctor — Even if these doctors appeared in a later outbreak, their image is one of the most well-known symbols of the bubonic plague in the world.

Introduction

We will start with the Black Death (1346-1353). You might have heard about the Great Plague, the Pestilence, or the Bubonic Plague. Well, they are all caused by the same bacterium, and the different names just reflect the different forms and symptoms of the disease. But exactly, what is it?

The Black Death was one of the most devastating pandemics in human history. Even if we do not know the exact number of deaths, it is estimated that it killed between 75 and 200 million people in Europe, Asia, and Africa. The disease was caused by the bacterium Yersinia pestis, which was spread by fleas that infested rats, which in turn, were close to humans (sounds like One Health right?). Once the infected fleas bit a human, the bacterium entered the body and caused the disease. After a human was infected, the disease could be transmitted from person to person through contact with cough droplets or by contact with contaminated objects.

Types of plague

When a person gets infected, the disease can develop in three separate ways depending on which part of the body is affected. The most common was the so-called bubonic plague. Initially, it causes fevers, chills, muscle aches, and headaches. After a few days, the lymph nodes become swollen and painful (called buboes, hence the name: bubonic) often rupturing and releasing pus, blood, and more bacteria into the environment. 

The second form of the disease is called the septicemic plague. A person suffering from this kind of plague develops a severe infection throughout the body given that the bacterium enters the bloodstream, and even if it has similar initial symptoms to the bubonic plague, here the skin turns black due to internal bleeding (one of the reasons behind the Black Death name), and the patient suffering from it also develops heavy vomiting and diarrhea. 

The third way is known as the pneumonic plague, which even if it is the less common one, is the most dangerous as it is highly virulent (it is transmitted through droplets) and affects the lungs causing serious respiratory issues. 

So, where did it come from?

We now know that the plague killed millions and that it had three different “varieties”. But, the question (as with COVID-19) is, where did it come from originally? Well, this is where it becomes really interesting. 

The Danse Macabre or the Dance of Death showing skeletons dancing — Art was heavily influenced by the plague. Many artists and painters found inspiration in the grim reality that the world was going through at that moment.

Until very recently, science was not very certain of the bacterium’s origin. We knew that it entered the Mediterranean via trade ships coming from the Black Sea and started spreading there, but regarding what happened before that the evidence was not clear. However, in 2022, European researchers published the results of a study where they dug up 14th-century graves from an unknown epidemic with tombstones marked with “pestilence” as a cause of death in cemeteries located in what is now Kyrgyzstan. By doing ancient DNA genomic analyses on seven of those buried bodies, they discovered that in fact, Yersinia pestis was the cause of death for these individuals. Moreover, they discovered that exactly around that same period, there was a massive diversification event of Y. pestis  strains, effectively creating the strains that years down would cause the Black Death pandemic.

They also compared these ancient DNA samples with modern strains to geographically locate the origin of the bacterium in the past. The results show that the most closely related strains are those coming from the Tian Shan mountains in central Asia, pointing at the region as the geographical origin of the Black Death.

What did we learn from it?

The massive impact that the Black Death had worldwide led to the development of several medical advances to effectively and timely control the spread of the epidemic. Some of the most important ones were:

Surveillance and reporting: The disease highlighted the importance of early detection and reporting of outbreaks. Governments developed major surveillance systems to keep track of where the outbreaks were happening, how hard they were impacting the population, and how they were evolving.
Quarantine and isolation: During the plague, many communities placed affected patients and their families in isolation to control the spread of the disease. Also, some cities started to enforce a confinement period for travelers coming from areas affected by the plague. These cities required 40 days (about 1 and a half months) to make sure that the travelers were not infected with the plague. That is where the word quarantine comes from, “quarantino” which is an ancient Italian word for “forty.”
Sanitary control measures: The plague also made the governments realize the importance of having a country-wide presence of early versions of hospitals, medical professionals, and other rudimentary sanitation systems to prevent and control outbreaks in a timely manner.
Scientific research: The Black Death was a major driver and catalyst for early scientific research on infectious diseases, public health, and sanitation systems. Given the major death toll that the disease exerted on the population, it became extremely important to understand the mechanisms behind the transmission and recovery of the plague.

Conclusion

There is a lot more to say about the Black Death, but we hope that you have learned something new about this incredibly significant disease. It is important to highlight that the disease is still alive, and even if major advances have been achieved to control it, there are still outbreaks in some developing countries. Please let us know if you liked this post, and keep an eye on our social media channels, we will be posting more famous epidemics soon!