The Great Epidemics of All Time


Have you ever wondered what in history has claimed the greatest number of human victims? Natural disasters? Famines? Wars? Well, as tragic as all these events have been, to figure out the enemy number one of Humankind, we need to focus on something invisible to the naked eye: pathogens (the microbes responsible for infectious diseases). Indeed, for millennia, epidemics have massacred unarmed people, leaving a long trail of mourning since the dawn of time.

In 430 BCE, Athens and its Empire challenged rival Sparta for supremacy over Hellas. The war plans of Athenian strategist Pericles failed significantly; the Spartan army devastated Attica and besieged Athens itself. The most terrible enemy, however, was not outside, but inside the walls: in the city where the germs of a terrible pestilence lurked; the historian Thucydides narrates what happened.

The raging of the disease is confirmed by the discovery of mass and hasty burials dating back to that time; yet, neither the Thucydides report, nor the human remains, allow us to identify without doubt the terrible biological murderer. Scholars have hypothesized that the epidemic could have been smallpox, typhoid, typhoid fever, plague, or even haemorrhagic fever, akin to today’s Ebola. What we do know is that perhaps as many as 100,000 people lost their lives; that is, over one-third of the population of Athens. This is an impressive number, far superior to that of the deaths caused by the conflict. Over the centuries, bacteria, viruses, and other pathogens continue to kill more than the sword.

In the newly discovered Americas, natives were suddenly exposed to microbes brought by Europeans. The immune system of these populations had never come into contact with similar infections, so it was completely unprepared to fight the diseases they caused. Flu, measles, smallpox, typhus, and cholera exterminated the Amerindians; it is a destiny well represented by the Taìno people who lived in the Caribbean. Six years were enough to reduce them to less than 500 survivors.

Although Europeans gave free vent to extreme violence, such rapid extinction was largely due to new diseases; particularly smallpox, which is the same infectious agent that allowed few Spaniards to prevail over the powerful and well-organized Aztec Empire. However, when it comes to microbes, trips are almost never one way. The conquistadores may have brought to the Americas illnesses until then unknown, but all studies suggest they brought back to Europe syphilis, which exploded with particular virulence in the old continent. The first major epidemic occurred in Naples during 1495, just three years after the discovery of the New World; it then spread rapidly throughout Europe, where—according to some scholars—it exterminated about five million people immediately in the following years.

Over the centuries, things have not changed much; 2348 years after the plague of Athens, Major Powers in Europe confronted each other in the bloodiest conflict fought until then, World War I, where armies were equipped with repeating rifles, machine guns, and airplanes. The German Imperial Army had the Paris-Geschütz (Paris Gun), capable of bombing the enemy capital from 130 kilometers away; but, all pales in comparison with what microscopic infectious agents can do.

After four years of conflict, on the armies on their last leg fell the most devastating epidemic of all time: the Spanish flu, fostered by poor hygienic conditions. It is estimated to have provoked 50–100 million deaths around the world between 1918 and 1919. During the 20th century, before being definitively defeated in 1980, smallpox again claimed 300–500 million victims; three times more than all the bloody conflicts of that century.

Original article published in SCIplanet magazine, Winter 2020 issue.

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