You've heard of people who don't wash their hands. They get sick easily, and often have chronic illnes that continues for a long period of time. It seems to go away for a month, but it comes right back.
People consume food that is contaminated they have gotten food poisioning. But it could be more then that.

You've also heard of parasites and how people get them when they travel to new countries, and places. But they all live here as well. As of today global deaths are caused more by parasites then cancer. Every year more people die of parasite infection than of cancer and the rates are slowly but steadily climbing.

Food intake is one of the most common ways to get infected by a parasite. Vegetables grown on farms, unless washed properly, fertilized with waste can transfer the eggs of parasites. When contaminated vegetables are injested parasites imediately latch on to intestines, the brain, muscles, tissues, bones and other parts of the body rich with blood. It can occur almost anywhere where food is bought, sold, harvested, and handled. Parasites could be living in your homes, and fancy five star resteraunts, so you must be careful. Not only through food intake can parasites inter your body they can be picked up from soil. Your hands may have dirt underneath your nails, and when you lift them up to bite your nails they parasites are injested. You forgot to wash your hands and it may cause you a life. Please be careful, wash your hands, don't consume raw meat, or unwashed vegetables. If you go out to eat and your vegeies aren't wet don't eat them.

Works Cited
for further information, cleansing options, and symptoms please go to...
http://www.puristat.com