A series of epidemics in Mexico that decimated the Aztec population could have been a deadly strain of Salmonella originating in Europe, a pair of studies finds.

A deadly strain of the bacterium – Salmonella Paratyphi C – was found in the stomachs of bodies unearthed from 16th Century cemeteries in the Mexican Highlands, reported in a study published on the preprint server BiorXiv. The bacteria was found in bodies buried during a major disease epidemic, known as a cocoliztli, between 1545 and 1550.

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"The 1545 cocoliztli epidemic is regarded as one of the most devastating epidemics in New World history," the study authors write in the paper. They used a genomic technique called MALT to pick out the ancient Salmonella DNA from other contaminating microorganisms and the human host DNA.

This particular strain of deadly Salmonella was also circulating in Europe about 300 years previously, finds a second BiorXiv paper. The bacteria was recovered from a body buried in the 13th Century in Norway.

They found that the pathogen had been causing disease in humans for at least 1,000 years. It first infected humans after spreading from pigs, they say, as Paratyhpi C was found to have descended from swine pathogens.

Deadly pestilence

"Really, what we'd like to do is look at both strains [in the pair of papers] together," Hendrik Poinar, an evolutionary biologist at McMaster University, Canada, who was not involved in either paper, told the journal Nature. This analysis could shed more light on whether the strains were closely related.

Aztec warriors
An illustration showing a meeting between the Spanish explorer Hernando Cortez (1485-1547) andMontezuma (1466-1520), king of the Aztecs. Hulton Archive/Getty Images

It's a widely accepted theory that major epidemics led to the collapse of the Aztec population, killing about 80% of Mexico's native people of the time in less than a century. The nature of the disease that caused the deaths, however, has been disputed. Measles, mumps and smallpox are among the candidates, which may have had a European origin, transmitted to the Aztec population by the 16th Century Spanish invasion.

However, climate variation has also been suggested as a cause for the disease outbreaks. Research into the climate of 16th Century Mexico suggested that heavy rainfall followed by drought brought bouts of haemorrhagic fever that coincided with the two major epidemics of the century.