No idea if they're connected to parasites or not, but a hot sitz bath with some Epsom Salts and white oak bark will do wonders. Make should Epsom Salts are completely dissolved in the water and make sure the water is as hot as you can possibly stand. White Oak bark is very high in tannic acid which will shrink swollen tissue such as hemorrhoids. You can get white oak bark capsules, and then just empty a few of those capsules in some boiling water and let it steep for a bit and then put it in your sitz bath along with the Epsom salt. soak for about 15 min. like that.
Witch hazel is another Affective natural cure
And of course Preparation H, or the generic version, is also great remedy.