Yes and no. parasite cleansing should be done 2-3 times per year - every year. The very first cleanse will remove the old, established infections and the ones there after will remove any new infections and will help to prevent getiing new infections.
Regular parasite cleansing will keep the parasites from "taking over" - in other words, if you should happen to pick up a parasite infection - the parasites will simply not have enough TIME to reproduce enough to cause major harm. Even if you pick up an infection - the next scheduled cleanse will get rid of it very quickly :)