[muawiyah]

The Americas had had a problem with hanta virus for thousands of years. That's what killed off the Indians AND delayed European invasion and settlement for a good century and a half after Columbus' voyages.

In what is now the East Coast of the United States, for example, the Indians OUTNUMBERED the newcomers until about 1648 ~ that's when a particularly bad winter combined with a slightly higher than normal incidence of several communicable diseases (probably could add in the flu to the situation), boosted the death rate among Indians and Europeans right through the roof.

The big difference between the two groups wasn't natural resistance ~ it was far simpler ~ Europeans could ship in an indefinite resupply of human beings, which they promptly did.

There are a number of good books on the market that cover the American population catastrophe of the 16th and 17th centuries.

[Eric in the Ozarks]

Mann, the historian, says the big difference was the lack of resistance. Only a comparative handful of Europeans arrived between 1519 and 1623. The indigenous population dropped from about 25 million to about 700,000 in about 100 years, a 97 percent reduction.
Hantavirius was called “Cocolitli” by central Americans. Small pox was the chief killer and is described unmistakably in 16th century drawings.