Artists' Interpretation of the state of an infected Dragon. The infection in this case was allowed to proceed for a full month as the Dragonlord bonded with her could not bear to slay her. It was reported that the pain was such that it overwhelmed the mind and resulted in behaviours more akin to a wild beast.
The Underworld's touch is a dreaded disease that is almost always fatal. The disease was first discovered when The Order of the Dragonlords attempted to use the Underworld as a means of transit to avoid the influence of Sydon. While some journeys were successful it was soon discovered that some sickened. The first sign was a rash that soon turned ashy grey. It left flesh dead to feeling and oddly spongy to the touch. The rash would spread and cause extreme pain to the individual. Many efforts were made to heal or stem the disease including flaying the infected skin and powerful cleric magic but nothing was able to stop the spread. The few cases where victims were cured involved amputation of the affected area as soon as the disease took hold, followed up by Dragon fire to seal the wound. After expeditions were sent underground failed to find the cause, The Order of the Dragonlords sealed most entries to the Underworld in an effort to stop it from spreading. Alas even now, almost five centuries hence, it will take hold in random places. If this happens it is of utmost importance that the surrounding area is purified.
This disease is unusually effective, being able to affect creatures that do not seem to experience other forms of sickness. There are records of Dragon's contracting the illness and it's suspected that Dragonlord Dourin Kobalos was felled by it although no corpse was found. Most worryingly however is unlike most ailments, this does not just affect creatures but the land itself. Villages where the plague takes hold alter entirely, the ground becoming grey and cracked and the buildings warping to match the curves of the ground. Many philosophers in the The Academy of Mytros proposed that everything was being reshaped to match what the Underworld looked like but as any infected area was quickly destroyed (and the inhabitants killed) they have not been able to fully witness a transformation. The longest the infection has been observed was a month whereupon the victim's eyes started glowing softly and various pieces started falling off. The subject was quickly put out of their misery and the responsible Academy members were fined for irresponsible research.
In a vision that Tryntia had, the whole of Mytros had been taken over by this plague, it having spread from gigantic chasms that had formed to connect the underworld and Mytros. The city was filled with victims of the plague intent on only one thing, spreading the touch. The disease had been rampant for years from what she could see and it had transformed the people it affected. Where eyes would normally be, a great hole had formed that extended almost to the back of the skull. The end result resembled a maddened caricature of a Cyclops.
There are of course claims that this is no disease but instead it is the will of Lutheria, punishing mortals for daring to breach the underground, but they are considered heresy and should not be considered.