In a village the characters hear rumors of a man that recently came through screaming of demon attacks and murderous insects. He was sweating and the village thought he was delirious and had a disease so quickly they chased him from the village.
The party will come across a dead man a few miles outside town. If they go through his belongings they find a large golden necklace with square cut emeralds in it. The necklace is cursed and will draw demon attacks at random intervals and insect attacks during the night. Eventually these attacks will kill them if they do not get rid of it or return it to its original site.
Alternatively it could be some gold coins that carry the curse to make the cause less obvious.