I had an experience with parasites from raw oysters or chicken liver. I'm pretty sure that it was the chicken liver, but since I ate them together, I can't 100% rule out the oysters (tho I had them before w/o any probs).
Parasites attach themselves to the intestinal wall, making them notoriously difficult to get rid of. Unlike bacteria or toxins, your body generally can't just flush them out, b/c they're hanging on for dear life. Not only that, there are 100's of different types, so even if you go to a doctor to test, there's no gaurantee they will test for the type you might be infected with. So the only real way to get rid of them is to either fast for a long time (starve them out), or to eat a large amount of the things that kill them and thier eggs.
Things that are really good at killing parasites and their eggs:
-garlic, lots of garlic
-ginger
-cloves (might be able to find whole dried cloves in the spice isle, if not, you can find it in a tincture)
-wormood (tho I think it's mildly toxic so you don't want to eat too much too often - also in a tincture)
-black walnut hulls - I could only find a tincture
Things that are mildly anit-parasitic
-onions
-very spicy peppers such as habanero
-apple cider vinegar (I've read they don't like acid)
-pumpkin seeds (only paralyzes them)
-cinammon
Now everything I read online was along the lines of... "combine x, y, and z together and do this 3 times a day for 4 weeks, then increase the dose [or change the ingredients] and take for another 4 weeks." If you're interested in a long term slow working cure, then there's lots of info on the internet for various regimens. I was not interested in taking tinctures for over a month, so I went in totally bonzai and got rid of them in a day. Here's what I did:
Although I ate lunch, it went right through me, as I hadn't eaten any ginger or garlic with my beef - for a whole month, food passed straight through me if I didn't eat garlic or ginger with it. I finally got cheezed off enough that I decided to eat only the things that would get rid of them, and keep at it until they were gone. So...
Instead of supper, I chopped up 3 large pieces of garlic (as in 2-3 of the pieces you would pull off the whole clove), about twice as much of ginger, and 2 habanero peppers, minus the seeds. I mixed it all with apple cider vinegar and drank/chewed. Probably I should have just minced in a food processor, as chewing it burned pretty bad. I ate most of it, and went to bed. The next morning I ate the rest. Almost immediatly I had diahrea - it smelled pretty awful, and definitely different than usual. Then I got some clove, wormwood, and black walnut hull tinctures and helped myself to generous portions (a good bit more than what the bottle says to take). Again, the same reaction, but milder than the first.
I wasn't really trusting of the tinctures - I don't trust anything that's much processed and tinctures seem to fit that bill - so I decided I would go find anything and everything I could that was anti-parastical, and mix together. So I went to the store and found some dried cloves, cinammon sticks, and pumpkin seeds. I started by eating just a bit of the pumpkin seeds. Then minced garlic, ginger, onions, dried cloves, and cinammon in a food processor. I mixed with water and added plenty more of the 3 tinctures I had. By this time it was afternoon, and I ate the rest of this horrid concoction, very bitter. Judging by the taste (I had to chew this up since it didn't mince very well), I assumed I would have an upset stomach very soon followed by some liquid diahrea. I actually had neither, and after a half hour or so, I started to feel rather energized. I let all that pass through until evening, and then ate a little supper, with more garlic and ginger (I wasn't takin no chances).
I haven't had any symptoms of parasites since. I did eat 2-3 pieces of garlic and plenty of ginger every day for the next few weeks, but it was mostly out of caution, and I don't think it was probably necessary, but it couldn't hurt... except for I smelt of garlic for a few weeks.
Like I said, kind of an all out knock out punch, and it works. Most of the herbs that kill parasites are VERY bitter and/or VERY spicy, and taste horrible in their raw, whole form, so expect that. Good luck, shout with questions.