Grausen

Grausen (GROW-zən; Germ. "horror") is a condition caused by a unicellular eukaryotic parasite called Daemoni adspicio (Lat. "I see the devil"), a species described in 2013 by Juliette Silverton. For centuries prior to this groundbreaking discovery in 2013, Grausen was an unexplained phenomenon dealt with in an urgent manner by the Wesen Council.

Cure
Daemoni adspicio are dependent on body temperature, so getting the victim's body temperature down to hypothermic levels will cause the parasite to leave the victim's body though the nose and ears where it will die.

History
Before Nick's encounter there was much confusion as to what Grausen were exactly. Some believed they were past Wesen spirits that invaded children, others believed they were mutations, but everyone acknowledged how dangerous they could be. In 1682, the Wesen Council communicated for the first time with Royals and Grimms regarding Grausens. They forged an agreement to have all Grausens "dealt with" because if left to grow into maturity Grausens have been known to become some of the world's most notorious psychopaths, sometimes wreaking havoc on entire continents. If there's even a possibility of a Grausen sighting, an individual must notify the Council, or else suffer the consequences.

Excerpt from Grimm Diaries
January 15, 1520

I hath heard of a being plagued by fits of violence in the hamlet of Wetsover.

''The being was no Wesen I have account of and perhaps not Wesen at all. A Grausen my kin called them in stories of olde.''

September 21, 1920 Atlantic City, New Jersey

''But I am left with a nagging question. I don't believe this is possession by any sort of devil or demon. I believe it is a disease, of what manner, I know not, nor how it is transmitted.''