UV only solves one part of the equation. UV kills the free swimming stage of the parasite and only IF the organism goes through the sterilizer. Once it's on the fish, that ship has sailed. And since most people don't have it set up that 100% of their water goes through the UV, it can only kill a fraction of the free swimmers at best.
Best prevention: Quarantine/observation/treatment if indicated, along with low stress, good water quality and varied diet.
There are a few different methods for treatment, depending on how aggressive you want to be.
My preference: Seachem Cupramine IN A QUARANTINE TANK ONLY!!!!! Never in a display - copper kills inverts.
Other options: Seachem Metronidazole with Focus in the food, (can be done in DT), and/or the same as a water treatment (QT ONLY!)
Hyposalinity to deter the growth/reproduction of the parasite. This is sometimes helpful but most often if used in conjuction with another method.
Jenn