The human body is literally crawling with hundreds of strains of viruses, yeasts and bacteria and other small foreign organisms. The digestive tract alone holds more than 1kg of bacteria. In the right balance, these organisms are necessary for proper digestion and nutrient absorption. We definitely do not want to be completely sterile. However, there are over 130 species of parasites which can cause up to 400 different diseases. Here is more information about what to look out for and how to manage them.