None of the fluke infections are endemic in the US except for Nanophyetus salmoncola, which is occasionally transmitted by salmonid fish in the Pacific Northwest. However, part of a patient's history may indicate residence or travel in one of the endemic countries. Thus, it is possible to diagnose fluke infections in the US and the ability to identify their eggs is necessary for a definitive diagnosis. Keep in mind that although not all of the trematodes covered in this course live in the intestines, they can all be diagnosed by finding their eggs in human stool specimens. One thing noticeable on many fluke eggs that are not seen in other types of worm eggs is an operculum, which is a little "lid" at the one end of the worm. Occasionally it can be flipped up or missing.
Table 2 shows diagnostic features of the flukes that live in the intestinal tract and biliary system, along with their typical geographic locations and means of how they are acquired. The following page will have charts of the flukes living in the lungs and veins.
Table 2. Flukes Living in the Intestinal Tract and Liver/Biliary System.| Species and Description | Image | Geographic Location | Means of Infection |
| Fasciolopsis buski "Giant intestinal fluke" 130-150 x 60-90 µm It is morphologically indistinguishable from Fasciola hepatica. |  (8)
| South and Southeastern Asia | Consuming metacercariae on uncooked acquatic vegetation |
| Heterophyes and Metagonimus | Similar to Clonorchis eggs; mostly indistinguishable from them | Egypt, Middle East and Far East, Siberia, Balkan states, Israel, Spain | Consuming metacercariae on undercooked fish |
| Nanophyetus salmoncola 87-97 x 38-55 x µm Similar to F. hepatica and F. buski, but smaller. |  (9) | Pacific Northwest US | Consuming metacercariae on undercooked salmon |
| Fasciola hepatica Indistinguishable from Fasciolopsis eggs 130-150 x 60-90 µm. This image has an open operculum, but that is not necessary for identification. |  (10) | Sheep and cattle raising areas of more than 70 countries, including parts of Europe, Latin America, Asia, Africa | Consuming metacercariae on vegetation |
| Clonorchis and Opistorchis ~27-35 x 11-20 µm Note opercular shoulders and a slight knob at the opposite end. |  (11) | East Asia into far eastern Russia | Consuming metacercariae on undercooked freshwater fish |
