The bark of Cinchona trees (from which quinine is obtained) was first described as a remedy for malaria by Jesuit missionaries in Peru. Protestant hostility toward Jesuits, however, led to a distrust of “Peruvian bark” in England. An apothecary’s apprentice named Robert Talbor warned patients to “beware of all palliative cures and especially that known by the name of Jesuits’ powder,” instead offering his own secret remedy. His treatment was highly effective, earning him a fortune. A year after his death, his “En­glish remedy” was revealed to be an infusion of cinchona powder mixed with opium and wine.

In the late eighteenth century, yellow fever was widespread in the Caribbean; case-fatality rates among British troops there were as high as 70 percent. The fate of French troops sent to Saint-Domingue to suppress a slave rebellion was even worse. “Evidence suggests the troops were actually an expeditionary force with intentions to invade North America through New Orleans and to establish a major holding in the Mississippi valley,” wrote the authors of a 2013 scholarly paper. Mortality from the disease thwarted Napoleon’s “secret ambition to colonize and hold French-held lands, which later became better known as the Louisiana Purchase.”

In 1942 a contaminated yellow-fever vaccine caused an outbreak of hepatitis B among more than 300,000 U.S. Army and Allied troops. Nearly 50,000 clinical cases resulted from the contamination, including 29,000 incidents of overt jaundice. There had been medical evidence of postvaccination epidemics of hepatitis in both men and horses since 1885.

“There are observances necessary for a healthy man to employ during a pestilence,” advised the first-century Roman medical writer Aulus Cornelius Celsus, “although in spite of them, one cannot be secure.” Best of all is “to go abroad, take a voyage. When this cannot be, to be carried in a litter, walk in the open before the heat of the day, gently, and to be anointed in like manner.”

During the fifth century, the body of a ten-year-old child was buried in the Umbrian town of Lugnano with a rock inside its mouth. The practice was part of a folk custom intended to prevent corpses from turning into vampires and infecting the living with malaria. “I’ve never seen anything like it,” said the lead archaeologist who uncovered the skeleton in 2018.

“People think this pandemic is an accident,” wrote Nassim Nicholas Taleb in May 2020 of the Covid-19 crisis. “It is not. It is part of the system we have built. When you read the history of England, Italy, and the Middle East, you read of frequent quarantines and lockdowns because of sieges and plagues. These were built into the economic landscape and into the costs of every merchant. So the cost of the pandemic and future pandemics should be set against gross domestic product figures. We must realize our real economic growth is much lower than our annual figures suggest because the disasters wipe out the growth of preceding years.”

In 1890 Russian botanist Dmitri Ivanovsky was commissioned to study a disease destroying tobacco plants in Crimea. Filtering the sap from affected plants, Ivanovsky discovered in 1892 the presence of a small parasitic microorganism invisible under great magnification—a virus—which he thought was a minuscule bacterium. In 1898 Dutch microbiologist Martinus W. Beijerinck became the first person to recognize viruses as reproducing entities distinct from other organisms.