I would add to this answer that whatever the full range of parasite killing/disabling benefits zappers provide, part of this range may possibly be the result of the given zapper producing an output frequency (of sufficient amplitude) and harmonics that covers known MORs - what Rife described as Mortal Oscilitory Rate.... apparently every bug / parasite / pathogen / virus has one. Granted, what Rife is alleged to have done in his earliest of work using his "beam" equipment, it is said to have generated an AC output of frequencies that included RF, some other anecdotes & snippets (especialy the Hoyland factor) indicates at least a few audio-range frequencies were also found to be beneficial, and of the more prominent scraps out there alleged to be from his decades of research indicates his earliest equipment utilized a carrier frequency (in the MHz range) upon which individual MOR frequencies could be (dialed in and ) piggybacked onto the carrier.... effectively a custom-form of radio broadcast fpr deeply penetrating a patient's body with these various MOR frequencies....... we may never know what he knew.