[Opisthorchis felineus] [Opisthorchis viverrini]
Trematodes (flukes) Opisthorchis viverrini (Southeast Asian liver fluke) and Opisthorchis felineus (cat liver fluke).
The adult flukes deposit fully developed eggs that are passed in the feces . After ingestion by a suitable snail (first intermediate host) , the eggs release miracidia , which undergo in the snail several developmental stages (sporocysts , rediae , cercariae ). Cercariae are released from the snail and penetrate freshwater fish (second intermediate host), encysting as metacercariae in the muscles or under the scales . The mammalian definitive host (cats, dogs, and various fish-eating mammals including humans) become infected by ingesting undercooked fish containing metacercariae. After ingestion, the metacercariae excyst in the duodenum and ascend through the ampulla of Vater into the biliary ducts, where they attach and develop into adults, which lay eggs after 3 to 4 weeks . The adult flukes (O. viverrini: 5 mm to 10 mm by 1 mm to 2 mm; O. felineus: 7 mm to 12 mm by 2 mm to 3 mm) reside in the biliary and pancreatic ducts of the mammalian host, where they attach to the mucosa.
Opisthorchis viverrini is found mainly in northeast Thailand, Laos, Cambodia, and central and southern Vietnam. Opisthorchis felineus is found mainly in Italy, Germany, Belarus, Russia, Kazakhstan, and Ukraine.
Most infections are asymptomatic. Most pathologic manifestations result from inflammation and intermittent obstruction of the biliary ducts. In mild cases, manifestations include dyspepsia, abdominal pain, diarrhea, or constipation. With infections of longer duration, the symptoms can be more severe, and hepatomegaly and malnutrition may be present. In rare cases, cholangitis, cholecystitis, and chlolangiocarcinoma may develop. In addition, infections due to Opisthorchis felineus may present an acute phase resembling Katayama fever (schistosomiasis), with fever, facial edema, lymphadenopathy, arthralgias, rash, and eosinophilia. Chronic forms of Opisthorchis felineus infections present the same manifestations as Opisthorchis viverrini, with in addition involvement of the pancreatic ducts.
Eggs of Opisthorchis spp. in wet mounts.
Adults of Opisthorchis spp.
Intermediate hosts of Opisthorchis spp.
Diagnosis is based on microscopic identification of eggs in stool specimens. However, the eggs of Opisthorchis are practically indistinguishable from those of Clonorchis. The adult fluke can also be recovered at surgery.
Serologic testing is currently not available for Opisthorchis infection in the United States.
More on: Morphologic comparison with other intestinal parasites
Treatment information for opisthorchis can be found at: https://www.cdc.gov/parasites/opisthorchis/health_professionals/index.html
DPDx is an educational resource designed for health professionals and laboratory scientists. For an overview including prevention, control, and treatment visit www.cdc.gov/parasites/.