During the Interregnum, when sorcery no longer functioned, there was no adequate treatment for many different types of disease.
This resulted in a series of damaging plagues, made worse by the invasions of the Eastern Kingdoms. (Since the Easterners had no sorcery even before the Interregnum, plagues have always been common in the East).
These plagues caused a resurgence in the need for skilled Pyrologists, such as Tevna, who burned bodies of the dead in order to limit the spread of the disease.
Upon the return of the Orb and the re-establishment of The Empire, the spread of plague has greatly dimished, restoring a greater sense of stability and greatly aiding the Imperial economy.