A healthy intestinal tract is a key to preventing attacks by various pathogens. Parasites can be fought with high doseages of such probiotic substances as Lactobacillus acidophilus, L. bulgaricus, and bifidobacteria. Treatments need to last for several months, however. The health and number of organisms making up the normal flora of the bowel needs to be strong in order to compete against potential pathogens. Intestinal parasites and yeasts can ravage the intestinal flora, preventing the vital manufacture and absorption of nutrients, causing the whole body to breakdown in some fashion.