Plague in the 21st Century

Plague in the 21st Century

This article relates to So Very Small

Thomas Levenson begins So Very Small, his history of the development of germ theory, with an account of the Great Plague that struck London in 1665. Although this was the last major outbreak to hit England, Yersinia pestis, the bacterium which causes bubonic and pneumonic plague, has survived—and indeed thrived—well into the 21^st century. As recently as 2010, the National Institutes of Health claimed that, thanks to a proliferation of trade routes across the globe, the "plague is more widespread today than it has ever been."



Thankfully, these days plague bacteria mostly limit themselves to the world's rodent population. As Levenson describes, modern sanitation and hygiene practices have ensured that the majority of humans no longer share so much of their personal space with rats—or, more importantly, the fleas which thrive in their fur and can transmit the disease to humans. But that doesn't stop new human cases of plague emerging even today. It might seem extraordinary, but the United States sees an average of seven plague cases every year, and the World Health Organization estimates the annual global figure to be in the thousands. That's a far cry from the tens of millions who died within less than a decade during the Black Death, but the disease can still be deadly. Pneumonic plague can kill within 24 hours and remains fatal in 100 percent of cases when left untreated.

In 2014, for example, plague broke out on the island of Madagascar. Although the spread of the disease was limited—with only 263 cases reported to the WHO—the average fatality rate was still over 25 percent, meaning one in every four people who caught it died. (This rate could be as high as 60 percent depending on how late the patient received treatment.) Similar outbreaks in the Democratic Republic of Congo, where the plague is endemic to certain regions, saw lethality reaching over 30 percent.

As Levenson outlines, the development of germ theory heralded the arrival of modern antibiotics, which can be extremely effective against ancient scourges like the plague. The result is that Yersinia pestis (in its current strain) is unlikely to cause the widespread devastation it once did. But antibiotics can only work in places where they're being administered, and cases can only be detected in facilities with the medical equipment to do so. It's little wonder then that, given what we know about the way the plague spreads, you're more likely to die from it in certain parts of Africa than anywhere else on the globe. What was once the great leveler—culling rich and poor alike—is now a disease of poverty, by its very definition proliferating among the kind of deprivation where its hosts—infected rats and fleas—thrive the best.

As the NIH admits, the plague "cannot be eradicated." Levenson celebrates the fact that scientific progress over generations means we can live more safely even alongside deadly microorganisms—but he also reminds us that progress never spreads itself equally. The story of So Very Small is that humanity has fashioned the tools to mitigate the worst effects of diseases like the plague; the story of plague in the 21^st century is that the poorest on our planet also need access to those tools that so many of us take for granted.

Reported Plague Cases by Country, 2013–2018 courtesy of Centers for Disease Control

Filed under Medicine, Science and Tech

This article relates to So Very Small. It first ran in the June 4, 2025 issue of BookBrowse Recommends.