The White Plague, also known by its scientific name Podosphaera dermatrophis, is a type of fungus that attacks human flesh. The fungus originated as a type of powdery mildew that commonly attacks most cucurbits (cucumbers, squash, etc) but mutated and spread to the human population of Cibola. It is non-discriminatory in attacking both living and dead/decaying human flesh, and is also known to attack other living or dead organisms. In the natural cycle of ecology, it is not uncommon for fungi to attack flesh, especially in helping to break down dead organisms into simpler forms. In addition, fungal diseases on living flesh are not uncommon (e.g. athlete's foot). The White Plague however was very different in that it was an extremely aggressive form of fungal infection. It also reproduced prolifically, thus spreading the infection at a rapid rate.
The undead Liches of Treisenberg were affected to such an extent that their entire population was halved, with the remainder fleeing to underground vaults and depths unknown. The surviving population of living humans of Treisenberg and, subsequently, Helderbourgh, were able to successfully develop a sulphur-based inoculant to wipe out the fungus. Unfortunately the cure came too late, as Treisenberg descended into a civil war spurred on by the mass deaths, resulting in the eventual formation of Helderbourgh.
The fungus, for its part, has since spread to Shireroth and Natopia, ravaging the populations of those two increasingly decrepit empires. Fungal reproduction is through spores, which cannot survive long distances over saline water. Therefore researchers suggest that the spores must have been transported to Benacia via trade goods. Determining a point of origin, however, has been extremely difficult, as several nations have a presence on Cibola, and the spores can survive for several years in products such as wood, soil, paper, produce and more. Some have even suggested biological terrorism, pointing fingers at such states as Goetia; but these claims are currently unfounded and merely conjecture.