If you are refering to aquired immunity
in which the fish develope a resistance to the theronts trying to find a host, then they will not be elimated. The cycle will continue as long as a fish host remains to become infected. The life cycle is therefore not broken only it's ability to reproduce enmass is restricted to a less noticable few.
's can be an effective aid but are by no means a cure. They can help reduce the amount of free swimming theronts
thereby speeding up the eradication when combined with an effective cure such as hyposalinity or chelated copper. UV
's will also not prevent the problem either only reduce the number of theronts
Treating the fish in a seperate QT will ensure all fish no longer carry any trophonts
to later infect any new additions to the tank. Remember that any new fish you add will not have this higher resistance to the parasite and will easily become infected. The higher numbers of theronts
could then also make it harder for the previously "conditioned" fish to resist the theronts