In absolute and relative terms the 1545 epidemic was one of the worst demographic catastrophes in human history, approaching even the Black Death of bubonic plague, which killed approximately 25 million in western Europe from 1347 to 1351 or about 50% of the regional population. The epidemic of cocoliztli from1545 to 1548 killed an estimated 5 million to 15 million people, or up to 80% of the native population of Mexico ( Figure 1). The Mexican population did not recover to pre-Hispanic levels until the 20th century. The 15 cocoliztli epidemics appear to have been hemorrhagic fevers caused by an indigenous viral agent and aggravated by unusual climatic conditions. The 16th-century population collapse in Mexico, based on estimates of Cook and Simpson ( 1). These droughts appear to have interacted with ecologic and sociologic conditions, magnifying the human impact of infectious disease in 16th-century Mexico.

Tree-ring evidence, allowing reconstructions of the levels precipitation, indicate that the worst drought to afflict North America in the past 500 years also occurred in the mid-16th century, when severe drought extended at times from Mexico to the boreal forest and from the Pacific to Atlantic coasts ( 6). Recent epidemiologic research suggests that the events in 15, associated with a high death rate and referred to as cocoliztli (Nahuatl for 'pest'), may have been due to indigenous hemorrhagic fevers ( 4, 5). The catastrophic epidemics that began in 15 subsequently killed an additional 7 million to 17 million people in the highlands of Mexico ( 1– 3).

The native people of Mexico experienced an epidemic disease in the wake of European conquest ( Figure 1), beginning with the smallpox epidemic of 1519 to 1520 when 5 million to 8 million people perished.

Death Letter by David W. Peters