Ask Lemmygrad

It's believed they had syphilis. But no other major diseases come to mind- perhaps because of the comparative lack of domesticated animals, or the smaller and less connected geographic area (compared to Afro-Eurasia), and perhaps because severe disease mutations would likely burn themselves out within such regions rather than travel the length of Afro-Eurasia like old world diseases...

There are a few, most notably syphilis

I know you didn't bring it up but the 90% thing is a myth. Rates were different for different outbreaks and many of the deaths chocked up to disease that contributed to the depopulation of Mesoamerica and the Gulf region (now US South) was due to mass slavery by the Spanish and Portuguese who were destroying villages and capturing slaves to work them to death mining silver and gold for a 7 year life expectancy in captivity.

Certainly some communities were hit extra hard by outbreaks, whole villages wiped out like the one the Mayflower colonists would inhabit with homes and food stores ready-made by the deceased.

However disease was consistently the largest killer during wars in the Colonial period. Outbreaks would kill half the population in the aftermath of wars throughout pre US and US history like that in the north east during the 1776 events and those in Oregon country right after Plateau wars in the 1850s and 60s.

Being displaced from sources of medicine, being displaced from clean water and food, losing elder knowledge keepers to the diseases, those elders were also more likely to be killed in a Conquistador's raid. There are many compounding reasons why disease was so rampant and deaths due to war usually came in the form of disease, for instance, some estimates put half the deaths in WW2 to disease and famine.

It is true, in a plainly quantitative sense of body counting, that the barrage of disease unleashed by the Europeans among the so-called "virgin soil" populations of the Americas caused more deaths than any other single force of destruction. However, by focusing almost entirely on disease, by displacing responsibility for the mass killing onto an army of invading microbes, contemporary authors increasingly have created the impression that the eradication of those tens of millions of people was inadvertent - a sad, but both inevitable and "unintended consequence" of human migration and progress. This is a modern version of what Alexander Saxton recently has described as the "soft side of anti-Indian racism" that emerged in America in the nineteenth century and that incorporated "expressions of regret over the fate of Indians into narratives that traced the inevitability of their extinction. Ideologically," Saxton adds, "the effect was to exonerate individuals, parties, nations, of any moral blame for what history had decreed." In fact, however, the near-total destruction of the Western Hemisphere's native people was neither inadvertent nor inevitable.

From almost the instant of first human contact between Europe and the Americas firestorms of microbial pestilence and purposeful genocide began laying waste the American natives. Although at times operating independently, for most of the long centuries of devastation that followed 1492, disease and genocide were interdependent forces acting dynamically - whipsawing their victims between plague and violence, each one feeding upon the other, and together driving countless numbers of entire ancient societies to the brink - and often over the brink - of total extermination.

Stannard, D.E. 1992. "American Holocaust: Columbus and the Conquest of the New World." Oxford University Press.

Even if the diseases brought by the colonizers were spread unintentionally which they werent it was all intentional. They spread it intentionally.