From Lost Fables Wiki
Comes from having mucous membranes exposed to the spores of the Deep Fungus, a type of fungi
Non-Infectious beyond the first host
Disturbing the wrong sort of fungus, commonly referred to as Deep Fungus, will release a cloud of spores, which, if they touch a mucous membrane, will begin to infect the person. Hosts are almost always Glubokiy or Karmeny Karlik, as they both eat lots of fungus, and collect fungi from the depths.
Immediately upon contact, the membrane it passes through will become irritated. Noses will run, eyes will water, lips and the tongue will swell, and all of the above will become intensely itchy. If not dealt with quickly, the fungus will spread to the host’s eyes and begin to go to work, starting to grow on the surface of the eye. Little black tendrils will slowly extend from the corners of the eye to the pupil, and begin to branch out to cover the whole thing after a time, until, over the course of a month, the entire sclera of the eye will be covered in black growth. Though the process is very uncomfortable, causing the eyes to be itchy and watery the whole time, the end result is not actually entirely bad, as the growth seems to fuse with the eyes. On the upside, this increases the subject’s peripheral vision greatly, and allows them to see almost perfectly in the dark, assuming there’s any light whatsoever. The downside is that light becomes agonizing for those infected.
The infection will never kill its host, and dealing with it is rather easy, though very unpleasant.
Light, even the light of a simple torch, will kill the fungus after a course of several, typically three, hours. This is an extremely agonizing process, leading many who contract the fungus to instead constantly wear dark-tinted glasses.