What caused the cocoliztli epidemics that killed most of Mexico's people (1545, 1576 and later)?

In 1545 to 1548 and 1576 to 1580, an epidemic the Nahua called cocoliztli killed perhaps 5 to 15 million and then about half of the remaining native population; lesser outbreaks followed until 1642, and similar ones in 1736 and 1813. Acuna-Soto and colleagues (2002) proposed a native hemorrhagic fever carried by rodents, the outbreaks following megadrought and then returning rain. In 2018 ancient DNA from 1545 victims at Teposcolula yielded Salmonella Paratyphi C (enteric fever). Our test: what was the weather in central Mexico, where most people died, before and during each epidemic?

Where it stands (25 October 2026): in central Mexico, the worst drought of the last 600 years ran from 1514 to 1539 (the conquest years) and was followed by the wettest four decades of that span, 1540 to 1580, in which both great epidemics struck. The famous 16th-century megadrought of the 2002 paper is a northern (Durango) signal. Year by year, the records disagree on whether epidemic years themselves were wet.