No, maw worm are not fatal however they are parasitic and inhabits the rectum of the humans especially in children. However, they can cause complications if left untreated. Guinea worm disease or dracunculiasis is a disease that is caused by guinea worm and is caused through contaminated water that contains water fleas with guinea worm larvae. The parasite migrates through subcutaneous tissues causing severe pain in the joints. No cure is available for the guinea worm disease till now.