Complex sentence: Moreta, while attending a Ruathan gather, first heard of a disease, later found to be caused by a mysterious Southern Continent feline, that was infecting all of Pern, including dragonriders and herdbeasts, although dragons were immune.
Split into simpler sentences: Moreta, while attending a Ruathan gather, first heard of a disease, later found to be caused by a mysterious Southern Continent feline, that was infecting all of Pern. The disease soon began infecting all of Pern, including dragonriders and herdbeasts, although dragons were immune.