Gut bacteria linked to cataclysmic epidemic that wiped out 16th-century Mexico

By Beth Mole

In the wake of the Spanish conquest of the Aztec Empire in 1521, waves of epidemics slammed Mexico. By 1576, the population, which had been more than 20 million before the Spanish arrived, had crashed to two million. One brutal outbreak in 1545 was estimated to have killed between five and 15 million alone—or up to 80 percent of the population.

But, like the other epidemics, the disease behind the 1545 outbreak was a complete mystery—until now.

Genetic evidence pulled from the teeth of 10 victims suggests that the particularly nasty bacterium Salmonella enterica subsp. enterica serovar Paratyphi C contributed to the scourge of fever, bleeding, dysentery, and red rashes recorded at the time. The genetic data, published Monday in Nature Ecology and Evolution, offers the first molecular evidence to try to explain what’s “regarded as one of the most devastating epidemics in New World history,” the authors conclude.

For decades, researchers have speculated on the disease—or diseases—that caused the population collapse. Spanish invaders are thought to have unleashed a throng of pathogens and plagues from the Old World, including small pox and typhoid. In addition, some experts think that severe drought during the time may have awoken some dormant, native plagues. But it’s been a hard issue to settle with so few surviving clues and vague historical accounts. The series of epidemics, including the one in 1545, are simply referred to as cocoliztli, the generic Aztec word for pestilence.

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