Todd McCaffrey 
Dragongirl 

Shortly after Fiona»s return to Fort Weyr, three Turns older and wiser, her queen, Talenth, is infected with the dreaded sickness that has consumed so many of Pern»s precious fire-breathing dragons. Talenth»s recovery and the recovery of all the other dragons of Pern is delivered by the unflagging efforts of Lorana and Kindan at Benden Weyr — but their one vital clue is only bought with the loss of all the dragons of Telgar Weyr.
Fiona is sent to relieve the distressed weyrfolk of the now-dragonless Weyr. When her queen, Talenth, rises to mate, Fiona finds herself not only Telgar»s senior Weyrwoman but in the center of the dilemma that confronts all Pern — how can the one thousand fighting dragons do the job of three thousand? And, if they can»t, how long will it be before all of Pern is consumed by Thread?