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Jan. 18 (UPI) -- Scientists have uncovered new clues to the germs responsible for killing millions of native people in 16th century Mexico. Still, unanswered questions remain. In the century that followed the arrival of the Spanish in the Americas, a series of pandemics wiped out 80 percent of Mexico's indigenous population. In some places, nine in ten people perished. The death tolls remain unmatched in history.
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One of the pandemics obliterated the Aztecs in southern Mexico. Between 1545 and 1550, the disease known locally as "cocoliztli" killed millions. Until recently, scientists struggled to identify cocoliztli.
New research, published this week in the journal Nature Ecology & Evolution, suggests the Aztecs were devastated by a rare strain of salmonella called paratyphi C.
Scientists identified the salmonella strain among the DNA from ten people buried at Teposcolula-Yucundaa, the only known burial site linked with cocoliztli.
Historical accounts of the disease and drawings of its symptoms suggest the pathogen was blood-borne. Those who were infected reportedly coughed up blood and suffered nose bleeds. But whatever caused cocoliztli, it left few discernible marks on the remains of its victims.
"This is one of the diseases that doesn't leave any visible clues on the skeleton," Åshild Vågene, a researcher with the Max Planck Institute, told National Geographic.
Scientists sequenced the genomes of individuals buried at Teposcolula-Yucundaa and compared the results to a database of pathogen DNA. Computer analysis showed the presence of paratyphi C was common among the DNA.
But despite headlines suggesting otherwise, the studies can't be certain that cocoliztli was a salmonella strain, or that salmonella was the primary driver of the pandemic that killed the Aztecs.
Cocoliztli is a word from Nahuatl, the language used by the Aztecs. It roughly translates as "pestilence," and historical accounts of the disease describe bleeding sores on the skin of the infected. According to Caroline Dodds Pennock, an indigenous historian at the University of Sheffield, such symptoms aren't typically associated with endemic fever.
Some historians suggest the cocoliztli could have been used to refer to a variety of illnesses afflicting the Aztecs during the 16th century. Pennock, who was not involved in the new study, suggests the Aztecs were not wiped out by a single pathogen, but a combination of threats.
"Such appalling mortality rates were not caused by a single, devastating plague," she wrote in The Conversation. "They reflect people who, lacking immunity to European diseases and suffering under colonialism, were battered by wave after wave of germs -- including flu, typhus, measles, smallpox and, almost certainly, enteric fever."
