''Grapefruit seed extract
Has been proven to be effective against over 800 strains of viruses and bacteria, 100 strains of fungi, plus a great number of single-celled parasites. No other antimicrobial can make such claims. Despite destroying harmful intestinal parasites, it does not significantly harm the normal bowel flora...''
Check the link to read the whole text; it has also a wealth of info on antiparasitic plants.