I've never had that happen to my eels,it has happened to my fish tank critters before.Some of the meds they offer for Ick control is for most fish,& it can kill invertebrate species such as eels,puffer fish,shark and more I just don't know them all.If you go to the pet shope just ask them.
I wouldn't try to cure them 1st it'll take to much time for the meds to fix them 2nd I would think the eels might have a different smell/taste to them & that would just suck JMO
5/0