[brian_cloutier]

The book mentions population density but quickly discards population density as the primary factor. Instead it focuses on domesticated animals. Eurasians had many domesticated animals and often lived in close quarters with them. The New World had an extreme paucity of domesticable animals and therefore much less exposure to disease vectors and therefore no major disease capable of wiping out populations. (pg 212-213)

[soapdog]

Yes, that is key! The lack of beasts of burden and domesticated animals in the Americas. People often overlook this when talking about "how could a whole continent be wiped out by pox"