I spent a great deal of time in the summer with my niece. She had confirmed ringworm. (which is fungal - not a parasite) It was a dry/scaly perfect circle on her shoulder blade. Anyway, she was treated with Lamisil cream. It didn't really clear it up though, it stayed the same - didn't get worse, didn't spread. But stayed the same for a long time.
Finally I took over the situation and bought her some pure tea tree oil. With in a couple of days of applying it thrice daily. It was looking smaller and not as "scaley".
So I would just suggest tea tree oil applied 3x per day for as long as needed.
Note: Grapefruit seed extract can irritate delicate skin - or even give a burning sensation. Depending on the strength/brand.