It seems to me that there were several bacterial/viral invasions mediated by human migration over the past -20,000 years. Each ice advance lowered the oceans and allowed populations to colonise the exposed continental shelf = migrate and fill interior niches. Ice melts and migrations are deterred. Populations endure their pathogens, and evolve their set of pathogens. This seems to have had 2-3 recurrences - the recent Spanish/UK/European colonisation killed over 90% of the indigines to the ends of the rivers. These infections were bidirectional but not symmetrical. The Americas bore the brunt of these deaths. Measles/smallpox/chicken pox/mumps being highly lethal(death rates varied but data is sparse). Europe got syphilis(disputed - but generally held).
Has there been any 'archeo-bacterial-viral' work done on this? I know bones/teeth can be used as proxies for some infections?