Dragonsblood — Todd McCaffrey

A mysterious epidemic is striking dragons, and the next deadly cycle of Threadfall is only days away. Somehow, dragonrider Lorana must find a way to save all the dragons--including her own beloved Arith--before they ... succumb to the sickness, leaving Pern undefended. No doubt the first colonists, who originally bred the dragons, possessed the advanced technology to find a cure. But over the centuries, that knowledge was lost.

Five hundred years in the past, a scientist foresees that a disease may ultimately destroy the dragons, and she is determined to find a way to change the future. Now two brave women, separated by hundreds of years but joined by bonds transcending time, become unknowing allies in a desperate race for nothing less than Pern's survival.