It is if you look at the liver! Sorry, I?m being facetious, so I?ll explain properly.
Parasites in the liver usually cause the surface to carry white spots or to become mottled.
Cutting the liver and the ducts within might reveal small, flat, dark brown creatures which are liver fluke; but in all cases where an infestation is present or suspected, the liver should be destroyed.
The rest of the carcass is okay to eat.