Table 1.

Effects of the K–T bolide impact on host populations and likely consequences on the contemporary virosphere.

Impact on host/vector population	Consequence for virus population	Favorable virus characteristics
Rapid extinction	Extinction unless alternative surviving host/vector species exist	Broad host range; multiple vector species
Slow progressive extinction	Extinction unless opportunity for adaptation to new host/vector	RNA viruses; mobile hosts
Contraction and isolation	Extinction unless host/vector survives in sufficient numbers to sustain transmission (Ro > 1); reduced genetic diversity; appearance of new genetic lineages	Persistent infection; vertical transmission; nonpathogenic
Migration	Survival unless vector unavailable; potential for exposure to and adaptation to new hosts/vectors	RNA viruses; broad host range; mobile hosts
Contraction and recovery	Survival unless host/vector populations contract to levels that cannot sustain transmission (Ro < 1)	Persistent infection; vertical transmission; nonpathogenic
Unaffected	Survival	All viruses