1. There are two types of parasites: endoparasites and external parasites. External ones live on human skin (like fleas, lice, itch-mites) and endoparasites affect the system from the inside. No one can feel safe, they can be anywhere: in water, in sand, in vegetables which were not washed properly, on money. Certainly you should take some precautionary measures, but sooner or later anyone of us can confronted with spongers.