Thought history was shaped by great men? No – by little germs

A plague doctor, depicted in an engraving from c1656 - Hulton Archive
A plague doctor, depicted in an engraving from c1656 - Hulton Archive

That infectious diseases are not just illnesses that happen to us but a fundamental part of who we are – and thus of our history – is the premise of this absorbing book. The microscopic living world of microbes and bacteria is, explains Jonathan Kennedy, director of global public health programmes at Barts and the London Medical School, essential to our survival.

Starting with the earliest humans, Pathogenesis takes us through millennia to show how outbreaks of infectious disease have destroyed millions of lives – indeed, whole civilisations – as well as remodelling the societies that survive. Our pre-history was punctuated by massive waves of migration that often resulted in one group, bringing with them diseases to which they were more or less immune, wiping out the indigenous population – or vice versa. One reason, for instance, for the successful emergence of homo sapiens from Africa into Europe was the fact that they interbred with the blue-eyed resident Neanderthals, thus gaining the latter’s immunity to European pathogens.

What gave infectious diseases their real start, however, was when nomadic hunter-gatherers switched to farming, as one-place living meant settlements and, later, closely packed towns that facilitated the transfer of pathogens from one person to another. Enter smallpox, polio – both visible in Egyptian mummies – and mosquito-borne diseases. Homer’s Iliad begins with a plague in the Greek encampment outside Troy; the Plague of Athens, believed to have been either typhus or smallpox, played a part in the war between Athens and Sparta.

Ancient Rome, despite its public baths (where the same water was used by thousands) was a filthy place, with high child mortality. “Anyone who survived until adulthood would have acquired immunity,” says Kennedy, “but people who came from outside, including those who came to conquer the city, were at high risk.” What finally did for Hannibal and his elephants was Italy’s endemic malaria. Far-reaching trade, in turn, brought many pathogens to densely-populated Rome. When the Antonine Plague (believed to be smallpox) struck in AD 165, followed by the Cyprian Plague in 250 AD, the army shrank so much that slaves and gladiators had to be recruited, the economy nosedived and the decline of the Empire was hastened.

Then, in 541 AD, came the most deadly of all pathogens: Bubonic Plague. This, the Justinian Plague, killed almost half the world’s then-population and raged for centuries. What gave it its longevity was that the rodents of Central Asia, gerbils and marmots, in whom it was endemic and who were largely immune to it, when forced by climate change to seek food elsewhere, came in contact with the black rats of the nearest settlements – who carried it to humans. Trade did the rest.

Probably the most famous outbreaks today are the medieval plagues, especially the fourteenth century Black Death – the most fatal pandemic ever recorded, with its death toll of 75 to 100 million. Social norms broke down, people starved, Jews were massacred, buildings razed and the plague itself was frequently seen as a form of divine retribution. It struck again and again all over Europe – in 1656, it killed half the inhabitants of Naples and Genoa, and allowed the rise of the Ottomans, whose nomadic life made them less vulnerable than those in tightly-packed cities. "Without the plague," says Kennedy, "it is inconceivable that the Ottomans would have been able to quickly establish control over [such] a vast territory." In Britain, with the Industrial Revolution, cholera raged through crowded slums, forcing state intervention over public health.

And finally, in our own times, Covid-19 arrived and transformed our lives, causing huge damage to industry, the loss of countless jobs and the closure of schools. It's estimated that the education of almost half the world’s students has been affected. Great swathes of social behaviour have changed, from a greater reliance on the internet to increased "pavement" life: thanks to social distancing, we learned the Continental habit of eating outside a café even in winter. Fewer people, I note, now kiss on meeting or parting. And without the virus, would we ever have had “WFH”?

Kennedy’s intertwined story of humanity and humongous disease is told lucidly and knowledgeably, with ample historical context. The latter section is filled with much detail – although I was surprised to see that Spanish flu, the great killer of the early 20th century (over 50 million worldwide), didn’t get a mention. As for the future, the next great pandemic, thinks Kennedy, might be from AMR (antimicrobiotic resistance), as bacteria have grown steadily more resistant to antibiotics, thanks largely to over-prescribing. His conclusion: just as the great improvement in public health came not from “cures” but from investment in proper sanitation and better living conditions, so our own best hope is to tackle today’s root causes of ill health, most of which, like bad housing, poor diet and unhygienic conditions, spring from poverty. “Reducing stark inequalities,” he writes, “would be a very good start”.

Pathogenesis: How Infectious Diseases Shaped Human History is published by Transworld at £25. To order your copy for £25, call 0844 871 1514 or visit Telegraph Books