Numerous parasites can be transmitted by food including many protozoa and helminths. In the United States, the most common foodborne parasites are protozoa such as Cryptosporidium spp., Giardia intestinalis, Cyclospora cayetanensis, Toxoplasma gondii, and Entamoeba histolytica; roundworms such as Trichinella spiralis and Anisakis spp.; and tapeworms such as Diphyllobothrium spp. and Taenia spp.

Many of these organisms can also be transmitted by water, soil, or person-to-person contact. Occasionally in the U.S., but often in developing countries, a wide variety of helminthic roundworms, tapeworms, and flukes are transmitted in foods such as

• undercooked fish, crabs, and mollusks;
• undercooked meat; raw aquatic plants such as watercress;
• raw vegetables that have been contaminated by human or animal feces;

Some foods are contamined by food service workers who practice poor hygiene or who work in unsanitary facilities.

Symptoms of foodborne parasitic infections vary greatly depending on the type of parasite. Protozoa such as Cryptosporidium spp., Giardia intestinalis, and Cyclospora cayetanensis most commonly cause diarrhea and other gastrointestinal symptoms. Helminthic infections can cause abdominal pain, diarrhea, muscle pain, cough, skin lesions, malnutrition, weight loss, neurological and many other symptoms depending on the particular organism and burden of infection. Treatment is available for most of the foodborne parasitic organisms.