Parasites refer to both endoparasites causing the infection within the body and ectoparasites causing infection on the surface of the body. Primary transmission is along the fecal-oral route and so the health emphasis is on hygiene, clean water, and cooked food. Infections caused by protozoa include head lice, giardia lamblia, entamoeba histolytica, blastocystis hominis, dientamoeba fragilis, and cryptosporidium. Notable helminths include pinworms, roundworms, and tapeworms. Common symptoms of parasitic infection include gastrointestinal distress, joint aches, chronic fatigue, excessive hunger, and immune dysfunction. Parasitic infections also contribute to a variety of major diseases including Crohn disease, ulcerative colitis, arthritis, and rheumatoid symptoms. In the United States, diarrhea caused by endoparasites is the third leading cause of illness.