Pandemics and the course of history

We think of pandemics as something out of the ordinary, a dangerous disruption to everyday life; but the reality is that they are a recurrent, even normal, feature of human history, viewed across the millennia. The process of industrialisation during the nineteenth century brought repeated waves of cholera, typhus and typhoid, all of which spread easily in the crowded and insanitary conditions of rapidly expanding cities that were attracting a constant flow of immigrants, many of whom lived close to the poverty line. Even so, the impact of cholera was not entirely negative. It was soon realised that the solution to its spread lay in better sanitation; the consequence in London was the construction of massive sewers that still serve the city.

Pandemics within modern cities have many antecedents, and not simply within urban societies. Thus we would probably want to include within the category of pandemics the diseases, including smallpox and measles, that wiped out maybe nine-tenths of the native population in the areas of the Americas conquered by Spain and other colonial powers in the aftermath of Columbus’s discovery of the route across the Atlantic. Sometimes this is cast as a European crime against native peoples, and there is no doubt that the heavy physical demands Columbus placed on the native people of his major acquisition, Hispaniola (today Haiti and the Dominican Republic) weakened still further what little resistance people had to the European diseases that arrived with the conquerors. But this, along with the devastating effects of the conquest of Mexico and Peru, was not an intended consequence of these invasions: the Spaniards wanted to make use of the manpower of the native population, but as that population died out they had recourse to the importation of black slaves, the beginning of the infamous Atlantic slave trade. One could therefore argue that the trade in black slaves across the Atlantic had its roots in the great American pandemics of the early sixteenth century. 

Europe had experienced its own devastating pandemic a century and a half earlier, with the arrival of bubonic plague in 1347. There is some evidence of small-scale outbreaks of bubonic plague, endemic among small rodents, along the famous Silk Roads that linked the area of modern Ukraine with the vast expanses of Eurasia, as fast east as China. The major Genoese trading centre in the Black Sea, Caffa in Crimea, was under siege by a Tatar army that used the bodies of plague victims as cannon fodder, catapulting them into the city and infecting its inhabitants; from there the disease spread on Genoese ships along the trade routes that led into the Mediterranean, arriving before long in Messina. Setting aside the multiple pandemics in the Americas, just mentioned, the Black Death is thought to have wiped out up to half of the population of Europe and the Mediterranean within about five years. In its pneumonic form it was most lethal – its mortality rate approached 100%. 

Recovery was severely hampered by its return again and again in the fourteenth century, and spasmodically thereafter. Its economic effects were drastic and we can talk literally of economic and social dislocation: large areas of the countryside were depopulated, and survivors often migrated to the towns where demand for workers was strong, significantly changing the balance between the rural and urban population. However, it is important to distinguish the short and long-term effects of the Black Death. Those who inherited wealth from deceased relatives often found themselves better off, with the result that demand for bettr food and for high and medium quality goods, such as cloths, expanded. A new and confident urban middle class emerged. Outside the cities, empty areas were given over to sheep and pastoral activity boomed in areas such as Spain and southern Italy. The Black Death effected an economic revolution. 

People learned to live with plague. Great cities such as Milan might lock themselves down. Quarantine was taken seriously. Plague increasingly became endemic, that is, confined to particular areas, with severe outbreaks in Milan in 1630 (memorably described by Manzoni), in London in 1665 and as late 1720 in Marseille. Europeans had no defence against this disease because it had been absent from the region for many centuries. Although the plague reported by the Greek historian and general Thucydides which took hold of Athens in 430-26 BC appears to have been typhoid rather than bubonic plague, the pandemic that hit the Byzantine Empire in AD 541-9 is now known to have been bubonic plague, and appears to have had similar effects to the Black Death: very heavy mortality, major economic consequences in the countryside as a result of population loss, and the shrinking of towns in parts of the eastern Mediterranean. 

In its pneumonic form this disease was spread by droplets in people’s breath, and many of the worst pandemics have been transmitted in this way, even when the bacillus or virus is totally different. The Spanish influenza pandemic of 1918-20 is thought to have killed as many as 500,000,000 people worldwide, and its spread was facilitated by the movement of armies at the end of the First World War – it was not in fact Spanish, and Spain had kept out of the war. But wartime deprivation had probably weakened resistance in many of the countries it reached. Mutations in the influenza virus have been watched carefully, bearing in mind events such as the Asian flu of 1957 and the Hong Kong flu of 1968. 

But such diseases can also lose some of their potency, to judge, perhaps prematurely, from Covid-19. A lesson from the history of the Black Death is that a bacterium or virus that wants to survive cannot risk exceptionally heavy mortality for a long period. In such cases it kills not just people but ultimately itself as well, since the presence of many fewer people mean that it loses the opportunity to spread.