alternatehistory.com

Despite the fact that no New World diseases devastated the Old World on the same scale as various Old World diseases, it is not true that the New World lacked virulent diseases altogether.

The balance of evidence (do read this article) suggests that a disease called cocoliztli, which caused 12 epidemics between 1545 and 1642, was an indigenous disease. The Spanish appear to have considered it so, since they were accustomed with various Old World diseases but simply called this new disease "cocolistle" or "the great pandemic."

However, it appears that cocoliztli was primarily a rural phenomenon, which helped protect the primarily urban Spanish although the Spanish and Africans still were affected. And thankfully it was unable to make the leap across the Atlantic that many Old World diseases did (overall it seems a very localized disease that only struck Mexico's highlands under specific environmental circumstances).

There is some evidence that a cocoliztli-like phenomenon may have contributed to the Classic collapse several centuries before European contact.

Your AHC is to make cocoliztli, or a similarly virulent American disease (cocoliztli may have killed as many as 80% of the population in one epidemic), spread and devastate the Old World. Bonus if you can sum up the consequences in various parts of the world.
Top