5. An unknown illness killed half of the indigenous population of Mexico in the 16th century
In the 16th century, a series of severe droughts plagued Mexico. In their aftermath, a recurring disease struck the indigenous peoples, their Spanish conquerors, and the African slaves the conquistadores imported to New Spain. The Aztecs called the disease cocoliztli. For centuries speculation was that the disease was a form of hemorrhagic fever, carried by the vesper mouse, which flourished in the rains which followed the droughts. More recent scholarship identifies the illness as a form of salmonella enterica. The disease spread throughout Mexico, and similar symptoms emerged in other regions of New Spain, suggesting to some that the disease originated with the Spaniards, who brought it from Europe.
The symptoms suffered were similar to some of those presented in other diseases, known to the Spanish doctors. They included typhus, measles, smallpox, and yellow fever. Cocoliztli presented other symptoms not shared with the above, and was invariably fatal. Spanish physicians and priests identified the disease as “God sent down such sickness upon the Indians that three out of every four of them perished”. That estimate of the death rate may be low. Some scholars estimated that 90% of the indigenous peoples of Mexico died of the disease combined with the effects of droughts, and the Spanish conquest of New Spain. Modern estimates attribute 2-2.5 million deaths, 50% of the population, to the disease itself.