Why did the Native Americans get sick when the Europeans came, but the Africans and the Asians didn't seem to be affected by European sicknesses?

I don't mean to be flip, but what's a European sickness? The diseases that caused the "virgin-soil" epidemics in the New World had all been endemic for centuries -- and likely millennia for some of them -- across Europe, Asia, and Africa. For example"

Smallpox -- it's origins are still a bit controversial; traditional explanation is from North Africa, but genetic information seems to suggest East Asia
Bubonic plague -- recent article using genetic sequencing also fingered China
Cholera -- was endemic in the Ganges river basic for centuries before colonialism caused it to spread throughout the world

The pre-Columbian world was still plenty interconnected. So what does it take for a "virgin soil" epidemic? This is certainly not my specialty, but there needs to be a population sufficiently cut off from reservoirs of disease such as to have a bottleneck effect. There is an example in Africa where natives were dramatically killed off by Old World diseases, and that would be the Khoi (ie, the Hottentots, though that's no longer a preferred term), who lived in the area of the Cape in what is now South Africa. There were cut off from the rest of Southern Africa by the Karoo. In 1713, a massive smallpox outbreak devastated their population (estimated 90% deaths), probably from a Dutch ship. The other big example is from Australia, where a smallpox epidemic killed a similarly large percentage of the aboriginal peoples (possible as a result of biological warfare on behalf of the English).

TL;DR: Africans and Asians didn't die off in impressive numbers from "European" diseases because they already had them -- and likely had spread some of them TO the Europeans in the first place.