Treatment:
Make a strong tea concoction with rosemary. Do not boil, just steep for 24 hours or more. Dip the cat in this (when just warm, not hot) up to neck and use hand to scoop some onto head without getting it inside eyes, nose or ears. Dunk cat in and out a few time, rubbing fur to rustle fleas out.
I always check animal again with flea comb before tossing out the bath water just in case they need another dunk.
If the animal will allow, choose to soak them for a minute or two.
*crazy cat tip: wrap cat tightly to hold legs against body (not harmfully) in a t-shirt (thin, so the concoction will penetrates well) so they can not rip you to shreds
Prevention:
5 drops lavender oil (most important)
5 drops lemongrass oil
5 drops cedar oil
*mix with tablespoon rubbing alcohol to break oils
*add two cups water
*spray animal with solution as needed (I do once a day if in the "wild") ensuring to avoid face.