Parasites can do an incredible amount of damage without being the obvious cause. For example, those that live in the intestines can cause digestive problems like flatulence, constipation, or diarrhea. They can cause malnutrition by leeching nutrients from their host, resulting in fatigue, apathy, depression, poor memory and concentration. Parasites can settle in the joints and muscles, form cysts, and create inflammations. Often the resultant pain is attributed to arthritis.
Parasites are able to travel almost anywhere in soft tissue, including the brain.
They can form granulomes in the lungs, liver, uterus, and other organs. They produce toxic metabolic wastes that can attack the central nervous system. This can result in restlessness, anxiety, and depression. Penetrating the skin, other parasites can cause rash, eczema, swelling, papular lesions, skin ulcers, or itching dermatitis. Normally, only the adult stage of these flukes occurs in humans.