Review | Professor rewrites the history of disease and explains why Covid-19 was inevitable

Plagues Upon the Earth by Kyle Harper, pub. Princeton University Press It is time to reassess the human race’s supposed dominance of the planet. “It’s a microbe’s world,” writes Kyle Harper. “We’re just living in it.” Plagues Upon the Earth – Disease and the Course of Human History, the University of Oklahoma professor of classics and letters’ timely account of how disease has shaped humanity’s development, is science writing at its most lucid. This is an examination of our particular disease pool, how we acquired it, what factors have shaped it, and how it has changed us and we have changed it. It is a view of the world through the eyes of our germs. Harper draws on ancient medical records and the writings of historic diarists but also on the latest in genetic analysis to chart the emergence and spread of various diseases, often in ways that contradict previously accepted accounts of their origins and transmission. Think 2020 is bad? 1937 was Hong Kong’s year from hell By the end readers will be able to tell their viruses from their bacteria, protozoa, helminths and fungi, and understand that while there are pathogens that specialise in exploiting us, many of the most harmful are generalists resident in reservoir species such as bats, marmots and great apes – at least until an overly close encounter with humans provides an opportunity for a developmental leap. Many then kill us too quickly for human-to-human transmission to lead to a pandemic, but others such as Ebola, HIV, and as we know all too well, coronaviruses, can establish themselves long term in human populations, causing widespread death. Viruses break into our systems and use them for replicating themselves. There is no consensus as to whether they are even alive, but these have always been among our worst enemies (smallpox, measles). It has become possible to travel between virtually any two points on the planet during the incubation phase of any infection no matter how rapid its course Kyle Harper, in Plagues Upon the Earth – Disease and the Course of Human History Many bacteria are integral to human health, but others cause diseases such as cholera, typhoid fever and bubonic plague, although this is really a disease of rodents. Protozoa are single-celled organisms that cause diseases such as dysentery, and are also often vector-borne, mosquito-carried malaria remaining to this day one of the planet’s greatest killers. Helminths such as tapeworms and liver flukes, and fungi are typically more of a nuisance, like athlete’s foot, with little impact on human history other than indirectly as crop diseases. But the other pathogens have often dramatically reduced populations, causing empires to collapse or stimulating societal change. The miasma theory – that diseases are caused by bad smells – may have been mistaken, but steps to reduce sickness from this source required better organised and more interventional governments, and the filth was reduced with beneficial effects that germ theory would later explain. Once governments were capable of their enforcement, compulsory vaccination programmes saw off dozens of diseases, some permanently. Once governments had sufficient financial muscle they could arrange for the mass chlorination of drinking water, and Harper examines whether increased wealth led to increased health, or vice versa. Yet at times he seems almost to have sympathy for these mostly invisible enemies. “Our success as a species has been a boon for our parasites, which are trying to accomplish the same biological ends as you or I: acquiring chemical energy that can be metabolised to do the work of replicating genetic information.” Globalisation has played a major role in the spread of disease, but not just in the sense, as Harper points out, that “it has become possible to travel between virtually any two points on the planet during the incubation phase of any infection no matter how rapid its course”. As far back as 5,000 years ago, the domestication of the horse and the invention of the wheel both allowed more rapid and widespread distribution of infections. As for the future, Harper observes that we need to become better organised, and to do away with the chain of preventable human failures that has left us in our current position. “The lack of transparency, especially in the first days, the bumbling global health response, the unconscionable failures of leadership will share part of the blame.” Perhaps the main lesson is that the emergence of Covid-19 was just evolution going about its normal business, and what Harper calls “a perfectly inevitable disaster”. The emergence of further threats to human well-being is equally inevitable.