Parasites, yeast and toxic bacteria can all be checked for with laboratory testing. A surprisingly large percentage of the population is infected with these "bugs". You do not have to travel to third world countries to contract a parasite. They are commonly ingested in food that has been prepared by an infected cook. When these pathogens are found, treatment usually involves some combination of herbs, medication and dietary changes. One laboratory I commonly use performs a "Sensitivity Test" on the toxic organisms isolated from stool samples. This involves exposing the "bug" to varying concentrations of different herbs and medication. The purpose is to see which compounds are most effective in killing the organism. In this way, treatment becomes customized and more effective.