The place I come from is called Hinamizawa. It's a small village just south of central Japan, with less than 2000 residents. Each one of these residents also carries the disease. It's called 'Hinamizawa Syndrome', but only a few people in the village know about it.
It's a silent disease, with various levels... Level 1 is impossible to detect, and level 5 is impossible to miss. Once someone develops the symptoms of the disease they're... overcome with paranoia and everyone around them will start looking like their enemies. They start to see illusions... hear people say things that weren't said, see them do things that weren't done... because of the illusions, they start behaving in an extremely violent manner. Eventually, they claw out their throat... and die.
The only thing that we know causes the symptoms to start is to... leave Hinamizawa, but there are also other things.
... Haha, sorry to get all serious on you all of a sudden.