Your instincts are guiding you in the right direction. Anything that kills fleas, ticks, mites etc. may work. The problem is, it seems to be in the blood.
If you start to have eye floaters this is a pretty good indicator. Keep working on killing all external manifestations of these things. They have to "come up for air" and that is when they are vulnerable. It may take a long time to get rid of, and make sure you do not get bitten by ANY insect.
I am researching a possible drug solution, but will take a while. Shroom