Contagion: How Commerce Has Spread Disease

Mark Harrison’s medical history books are always big. Contagion is another masterful reach across continents and time, beginning in the 14th century and ending today.

It is a history of disease and a history of commerce in equal measure. The premise is familiar: infectious disease always tracks along commercial routes, deriving from, but also threatening, the more productive versions of exchange represented by trade. Almost everyone who writes about the history of contagion notes this. Few offer the historical substance behind the commonplace observation, however. None has done so with Harrison’s combination of carefully executed detail and grand scope.

Conventionally, a world history of contagion begins with the meeting of the Old World and the New, the “Columbian Exchange”, in environmental historian Alfred Crosby’s enduring phrase. But this book’s claim to “world history” status is immeasurably strengthened by Harrison’s decision to open with continental Eurasia instead: the less familiar set of trading and disease networks that stretched across the Mongol Empire, the Levant and Christendom. Not maritime but territorial commerce; not 16th-century syphilis but 14th-century plague.

There is a permanent tension at the heart of the matter that has driven the history itself, and Harrison’s account of it. On the one hand, the spread of disease plainly needed to be addressed. Increasingly it became the job of states to do so. On the other hand, minimising contagion through quarantine or sanitary measures always came at a commercial cost: the ruin of perishable goods; the disruption to return schedules; perhaps the suspension of trade altogether. Unsurprisingly, powerful merchant interests sought to undermine the efficacy of quarantine. Harrison shows just how high the stakes were, as this basic scenario played out repeatedly over time, within and between states, merchants, transport companies, and emerging health and commercial regulatory bodies.

Harrison works with the idea that managing disease, “coping with plague”, was a key driver for the development of states themselves: their centralisation, administrative mechanisms, local powers and need for international agreement. The last point, often enough, was less about how to impose quarantine than how to minimise it, thereby enabling international trade.

Contagion is at its most lively when Harrison recounts episodes of contagion-based sabotage. There was occasional traffic in misinformation about which port and which vessel housed cholera, plague or yellow fever. By the 19th century, notification of disease had formed the basis of some of the earliest international negotiations, treaties and agreements, and so this was dirty diplomacy indeed. It was also, Harrison suggests, war by other means. The episodes suggest that the twinned phenomena “contagion” and “commerce” were really triplets, joined by “communication”. The book should also be read, then, as the long back-story to information-driven biosecurity measures today.

There are very few historical topics that present genuinely similar components across societies and centuries: this is one. And this is why the tensions and the politics are so instantly recognisable, as Harrison tracks through 14th-century Genoa, 19th-century Mecca and 21st-century Hong Kong. Arguably, the only kind of trade that remains untouched by contagion now is virtual trading in currency and stocks. That, of course, is subject to a different species of virus altogether. In all other respects this long history remains with us, if anything heightened by globalised economies and the mass movement of people, and by dangerous concentrations of (and traffic between) animal and human bodies. Harrison presents us with a magisterial history that is as much about the precarious present as the past.