Personally, I think parasites exist in most peoples imaginations.
Last nights chinese takeout can yield all sorts of scary monsters.
Some of the people on curezone must live in caves and eat bat guano to have so many parasites inside of them.
I've seen people on certain forums claim to have expelled 'tons' of parasites!
Anonymity is a posters best friend, you can pretty much say whatever you want.
And fortunately for them, there always seems to be someone that will believe them!