Parasites - Opisthorchis Infection

L: Adult of O. felineus. R: A large group of fish. Fish do not have to ingest anything because the parasite can encyst under the scales or in flesh. Eating infected fish can result in Opisthorchis infection


Opisthorchis species are liver fluke parasites that humans can get by eating raw or undercooked fish from areas in Asia and Europe where the parasite is found, including Thailand, Laos, Cambodia, Vietnam, Germany, Italy, Belarus, Russia, Kazakhstan, and Ukraine. Liver flukes infect the liver, gallbladder, and bile duct in humans. While most infected persons do not show any symptoms, infections that last a long time can result in severe symptoms and serious illness. Untreated, infections may persist for up to 25–30 years, the lifespan of the parasite. Typical symptoms include indigestion, abdominal pain, diarrhea, or constipation. In severe cases, abdominal pain, nausea, and diarrhea can occur. O. felineus, in addition to presenting with the typical symptoms also seen in O. viverrini infections, can present with fever, facial swelling, swollen lymph glands, sore joints, and rash—similar to the signs and symptoms of schistosomiasis. Chronic O. felineus infections may also involve the pancreatic ducts.Diagnosis of Opisthorchis infection is based on microscopic identification of parasite eggs in stool specimens. Safe and effective medication is available to treat Opisthorchis infections. Adequately freezing or cooking fish will kill the parasite.

Images: Left: Adult of O. felineus. Right: A large group of fish. Fish do not have to ingest anything to become infected because the parasite can infect fish under the scales or through the flesh. Eating infected fish can result in Opisthorchis infection. (Credit: Web Atlas of Medical Parasitology and the Korean Society for Parasitology, NEFSC/NOAA)