"The disease came from animals that didn't exist in the Americas," said Elsa Malvido, a Mexican colonial historian who has spent 40 years tracing the origins of the diseases that decimated the Aztecs.
argues that the later epidemics were caused by bubonic plague carried to Mexico by black rats aboard the Spanish galleons.
cites indigenous codices that describe a plague of rats preceding the epidemics.
acknowledged, "As long as I don't have a skeleton to extract DNA, of course, these are all hypotheses."
AcuÃ±a-Soto counters that the disease doesn't fit the pattern of bubonic plague, which he
said tends to spread inland from coastal areas and kills a minority of those infected.
In contrast, he
said, cocoliztli originated in central Mexico City and had the most devastating impact in the highlands.
The later epidemics coincided with two major droughts, which may have magnified the impact of the disease, he