Hulda Clark mentions in her books that the zapper does manage to kill big (not microscopic) parasitic worms inside the body, and that's why she recommend to use herbs containing anti helminth substances.
The electric signal produced by a zapper seems useless against big (not microscopic) parasitic worms and many are big (not microscopic) so to say that the zapper can kill all kinds of parasites in a human body (as you have written several times or as zappers sellers suggest, is deceptive and false (or please show me a proof))
However it may affect the small (microscopic) parasites in the blood, in the lymph, in the skin, in the others fluids) but will it kill them or just annoy them ? Again there is no proof of a killing effect. Only vague suggestions and hype.