In recent years, there have been dire warnings of antibiotic resistance and uncontrollable pandemics. And the general public would be wise to listen. In spite of our knowledge of bacteria and viruses, we can still be caught by surprise, as can be seen from the recent Ebola outbreak. Those who do not learn from history are doomed to repeat it, as George Santayana famously observed, and it is therefore useful to know a little about the greatest of pandemics: the so-called "Black Death" that devastated medieval Europe.
Historians debate many aspects of the 14th century plague, from its nature to its effects. However, they do at least agree on the dates. The disease originated in China in the 1330s. Over the subsequent decade or so it killed around 25 million people, before reaching Turkey in the early 1340s, carried either on ships or along the Silk Road.
In 1346 it struck the Crimea. From there it moved around the Mediterranean coast, up through France, into the UK, then on to Holland, Germany, Scandinavia and Russia. Generally, it seems to have spread through the coastal cities, moving from the Crimea to places like Venice, Naples, Marseille, etc, and entering England through the Channel ports.
In just six years, between 1346 and 1352, it killed around a third of Europe's population, though some believe it to have been as much as 60 per cent! But Europe was not the only place to suffer; during the 14th century, the world's total population fell from 450 to 350 million. Though no part of Europe was spared, some were hit worse than others. The island of Sicily, for example, lost over half of its population, while Denmark did not return to its 1300 level until 1801.
As if all this were not scary enough, the disease reappeared over the following centuries, though it never again inflicted losses on such a scale. Samuel Pepys, for example, nervously records rumours of plague deaths in his famous diary. And even as late as the 1720s, Daniel Defoe, author of Robinson Crusoe, published A Journal of the Plague Year, describing a late 17th century outbreak in London.
Of course, those living through the horror had no idea of its cause. To observers, it must have seemed like the end of the world. Thanks to modern microscopes, we know that disease is caused by viruses and bacterium. The inhabitants of 14th century Europe did not know this and, given the religious temper of the time, it is unsurprising that many thought it a divine punishment. Others argued that it accumulated in the air. This explanation, known as the "miasma theory," persisted into the 19th century.
People did recognize, however, that it could be spread from one body to another. In 1346, for example, plague broke out in the ranks of a Tartar army besieging Caffa in the Crimea. In what is perhaps the first example of biological warfare, the Tartar commander ordered the corpses of the dead to be catapulted into the city, where the disease then spread.
For a long time, historians assumed the bubonic plague was responsible. This is caused by a bacterium known as Yersinia pestis, which exists in rodent populations. It causes three different forms of plague, the bubonic being the best known. There are still several cases each year. Thankfully, however, they can now be treated with antibiotics. Left untreated, around 80 per cent die within a week. Modern antibiotics have reduced this to around 11 per cent.
In late 19th century India, British and Indian doctors studied outbreaks of bubonic plague and tried to understand its nature and movements. But it was to be the Swiss bacteriologist Alexandre Yersin who identified the bacillus responsible (hence the name Yersinia). It was then hypothesized that fleas had spread the bacterium in the 14th century. The flea bites the rat, absorbs the bacterium, goes on to bite a human being and thus spreads the disease.
In 1894, Yersin was part of a team of experts who travelled to Hong Kong to study an outbreak. But it was Paul-Louis Simond who, in 1898, linked the spread of bubonic plague to flea bites. Doctors also noted similarities between the symptoms and those described in the 14th century. When infected, the individual develops boils or swellings (known as buboes in the medieval world). These tend to appear in the groin or along the neck. The lymph nodes then fill with pus and swell.
Not everyone agrees with the bubonic plague theory, however. In the 1970s, it was challenged by the British bacteriologist J. F. D. Shrewsbury. In 1984, the zoologist Graham Twigg also disputed it, arguing that the Black Death was in fact caused by a form of anthrax. Later, Susan Scott and Christopher Duncan argued that it was more like modern Ebola. Numerous reasons exist for such skepticism. For example, many argue that flea bites do not explain the speed at which it spread.
In any case, the psychological impact must have been enormous. The rigid feudal system that dominated Europe was shaken to the core. Landowners, who had previously considered their tenants little better than livestock, now found themselves having to cajole, flatter and even pay their remaining peasants to care for the land and bring in the harvest.
Whatever the cause, the sheer scale of suffering and death was appalling. Whole villages were quite literally wiped out. And the worst hit towns must have resembled a post-apocalyptic movie.
First, and most obviously, there was sheer ignorance. Even the most sophisticated and observant knew nothing of viruses or bacteria. Health and illness were instead explained through the four humours. The body, so the theory went, is composed of four fluids: phlegm, blood, yellow bile and black bile. When these are in perfect balance, the individual feels healthy and happy. When one appears in excess, or diminishes, illness follows. Doctors tried to rebalance these humours by literally "bleeding" their patient, or by prescribing herbs and flowers.
Another interesting idea is known as the "disease pool theory." Until very recently, human populations were isolated from one another. Europeans, East Asians and sub-Saharan Africans each established a kind of equilibrium with the various diseases that ravaged their communities. In other words, within discrete zones the inhabitants built up a resilience, or immunity, to the more common diseases.
Disease is far more lethal when introduced to a population never exposed to it before. The best known example is Columbus' arrival in the Americas. The European traders and explorers who followed brought with them diseases like measles and smallpox. The American Indians had no immunity to such things and so died in their millions. In the case of the Black Death, it evolved in the Asian disease pool and was brought to the Western pool by the Tartars. Europeans, like the Indians a few centuries later, had evolved no immune response.
Experts often warn of antibiotic resistance, and when one considers an event like the Black Death it is easy to understand their fear. In general, people shrug their shoulders and assume that science will develop a solution. Or they dismiss pandemics as medieval: something that only happens in times of ignorance and superstition. Surely, they think, that could not occur today, not with our knowledge of viruses and bacteria.
But it has happened. In recent years, there have outbreaks of Zika, SARS, Swine Flu, and, of course, Ebola. Between 2014 and 2016, around 28,000 people were infected with Ebola, half of them fatally. Another 'Black Death,' though unlikely, is possible.
Along with an increasing resistance to antibiotics, there are several other reasons for this threat. First, the world's population is still growing. And it is growing fastest in Africa, the least developed part of the world. These ever-increasing numbers are also moving from the land into the cities. Urbanization is certain to be a major trend of the 21st century. By 2050, for example, two-thirds of the world's population will live in towns or cities.
So you will have lots of people crammed together, enabling disease to spread more quickly and infect more of them. It will also put a strain on sanitation systems, increasing the spread of disease. A growing population, combined with urbanization, also means a greater demand for food, which means more animals being bred for meat. Unfortunately, animals tend to harbour infectious disease. Cattle, for example, spread TB, while poultry created the avian flu outbreak.
Climate change is another cause for concern. This will mean more heat and more rain. That in turn will mean more insects and more waterborne disease. It will also mean more natural disasters. Floods, famines, and droughts will encourage people to migrate in huge numbers. For example, there may be a mass exodus from sub-Saharan Africa into Europe.
In any case, people are already moving around the world on a scale never seen before. The different races testify to the fact that large populations were isolated from one another for long periods of human history. Today, you can fly from New York to Tokyo in a few hours. And in the near future we will invent even quicker ways of moving around.
The Black Death was an exceptional event. And even the most pessimistic would have to acknowledge that we understand a great deal more than our medieval ancestors. Horror on such a scale is unlikely today. However, that does not mean it has nothing to teach us.