Why don't you try coconut oil? Coconut oil has powerful antibacterial, antifungal, antiparasitic, antiprotozoal, etc. properties/benefits. Maybe the lice are thriving because of these microorganisms. If it is, then coconut oil should be able to help you. Give it a fair shot. You have nothing to lose.

Frederick
Coconut Oil Central - The Home For Premium Coconut Oil Information