Black Death And Dark Memories

Bubonic plague has struck several times in the past 2,000 years, killing millions of people and altering the course of history. Each epidemic amplified the fear that came with the next outbreak.

The disease is caused by a strain of bacteria, Yersinia pestis, that lives on fleas that live on rats. But bubonic plague, which became known as the Black Death, also can be passed from infected person to infected person through respiratory droplets, so it cannot be eradicated simply by killing rats.

Historians describe three great waves of plague, said Mary Fissell, a historian at Johns Hopkins: the Plague of Justinian, in the sixth century; the medieval epidemic, in the 14th century; and a pandemic that struck in the late 19th and early 20th centuries.

The medieval pandemic began in 1331 in China. The illness, along with a civil war that was raging at the time, killed half the population of China. From there, the plague moved along trade routes to Europe, North Africa and the Middle East. In the years between 1347 and 1351, it killed at least a third of the European population. Half of the population of Siena, Italy, died.

“It is impossible for the human tongue to recount the awful truth,” wrote the 14th-century chronicler Agnolo di Tura. “Indeed, one who did not see such horribleness can be called blessed.” The infected, he wrote, “swell beneath the armpits and in their groins, and fall over while talking.” The dead were buried in pits, in piles.

In Florence, wrote Giovanni Boccaccio, “No more respect was accorded to dead people than would nowadays be accorded to dead goats.” Some hid in their homes. Others refused to accept the threat. Their way of coping, Boccaccio wrote, was to “drink heavily, enjoy life to the full, go round singing and merrymaking, and gratify all of one’s cravings when the opportunity emerged, and shrug the whole thing off as one enormous joke.”

That pandemic ended, but the plague recurred. One of the worst outbreaks began in China in 1855 and spread worldwide, killing more than 12 million in India alone. Health authorities in Bombay burned whole neighborhoods trying to rid them of the plague. “Nobody knew if it made a difference,” the Yale historian Frank Snowden said.

Dissecting rats in New Orleans in 1914 for signs that they might be carrying bubonic plague.

Dissecting rats in New Orleans in 1914 for signs that they might be carrying bubonic plague.Credit...Corbis, via Getty Images

It is not clear what made the bubonic plague die down. Some scholars have argued that cold weather killed the disease-carrying fleas, but that would not have interrupted the spread by the respiratory route, Dr. Snowden noted.

Or perhaps it was a change in the rats. By the 19th century, the plague was being carried not by black rats but by brown rats, which are stronger and more vicious and more likely to live apart from humans.

“You certainly wouldn’t want one for a pet,” Dr. Snowden said.

Another hypothesis is that the bacterium evolved to be less deadly. Or maybe actions by humans, such as the burning of villages, helped quell the epidemic.

The plague never really went away. In the United States, infections are endemic among prairie dogs in the Southwest and can be transmitted to people. Dr. Snowden said that one of his friends became infected after a stay at a hotel in New Mexico. The previous occupant of his room had a dog, which had fleas that carried the microbe.

Such cases are rare, and can now be successfully treated with antibiotics, but any report of a case of the plague stirs up fear.