Given the number of new arrivals that was a death rate to equal the worst Indian death rates.
Recall, at the time of initial settlement (1609) Virginia was just now at the end of nearly half a century of semi-arid conditions within which was a 17 year drought sufficient to have driven EVERYONE to live above the Fall Line. Those conductions always presage a major hanta virus outbreak once the drought breaks and the grasslands return.
Other historians have noted a similar period up the coast in the decade prior to the 1646-48 die-offs.
It was not the case that white folks just stood around and watched Indians died. Everybody died. The whites had backup resources in Europe. The Indians didn't.
Mann's estimate of 25 million is far too low. The agricultural base extant in the Americas at the time of first contact was far too large for such a small population.
Even if the Indians had had superior technology and were discovering Europe and Africa, they'd still died off in the Americas ~ as they had been doing for thousands of years.
There are some history writers who would agree; 25 million is probably on the low side. I agree, climate changes moved or wiped out large numbers.
If these estimates are correct, central and south America had a larger and healthier population than most of Europe.
It would be interesting to see a graph showing the European and native populations from 1510-1800.
As I recall from reading early accounts, settlers in Jamestown Virginia suffered a lot from malaria and typhoid fever. http://www.u-s-history.com/pages/h519.html