Electric magnetic fields are everywhere. Any device that generates electricity creates a field....even the earth itself. The point being made is that HIGH sources of EMFs are to be avoided. If the zapper creates a HIGH source of electric magnetic fields, it will decompose the oxalic acid within the blood. The strength of the field can only be determined through use of a gauss meter.
I can only suggest that you ask yourself if you truly believe that the zapper is effective. If parasites are present, oxalic acid will effectively kill them. As mentioned before.....ask any beekeeper. The use of oxalic acid on beehives kills all invading mites and does not harm the bees in any way. If the parasites within the body are exposed to the blood enriched with oxalic acid their chances of survival are next to none.