Hmmm... It's so funny to talk about this kind of stuff in this manner, but here goes.
I have always found the Master-Cleanse to be sufficient in passing all the icky critters from my bod. And, for myself anyway, its not like they came out wiggling and woogling and waving hello. They were tiny and seemed pretty much dead to me.
As far as herb goes, I wonder if acidophilus might do the trick. I have a bottle of it right here in front of me and it says it "encourages intestinal microflora balance". I had just assumed this meant it "ate" up the icky critters. Regardless, this stuff has never failed me when I have a stomach virus.