Zapper works where current goes. A lot on blood or lymph, very little, or not at all on hollow organs like the intestinal track. So don’t count on a zapper to kill parasites there. But…
Occasionally, there is enough electric charges accumulated there, to disturb the intestinal flora, specially if you zap for a looong time (1h and more) or use a zapper using frequency effect.
Note : A zapper doesn’t makes a difference between “good” or “bad” bacteria. It kills them all, and let us complain about the missing good ones (:-)
Everyone reacting on a different way to a zapper’s session, have some probiotic handily, and take some as needed. But definitively, the main effect of a zapper is not “there”