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Opisthorchiasis

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[Opisthorchis felineus] [Opisthorchis viverrini]

Causal Agents

Trematodes (flukes) Opisthorchis viverrini (Southeast Asian liver fluke) and Opisthorchis felineus (cat liver fluke).

 

Life Cycle

Lifecycle

The adult flukes deposit fully developed eggs that are passed in the feces The number 1. After ingestion by a suitable snail (first intermediate host) The number 2, the eggs release miracidia The number 2a , which undergo in the snail several developmental stages (sporocysts The number 2b, rediae The number 2c, cercariae The number 2d ). Cercariae are released from the snail The number 3 and penetrate freshwater fish (second intermediate host), encysting as metacercariae in the muscles or under the scales The number 4. 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 The number 5 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 number 6. 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.

Geographic Distribution

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.

Clinical Presentation

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.

 

Eggs of Opisthorchis spp. are 19-30 µm long by 10-20 µm wide and are often indistinguishable from the eggs of Clonorchis sinensis. The eggs are operculated and possess prominent opercular ‘shoulders’ and and abopercular knob. The eggs are embryonated when passed in feces.
Figure A: Egg of O. viverrini in an unstained wet mount of concentrated stool. Image taken at 400x magnification.
Figure B: Egg of O. viverrini in an unstained wet mount of concentrated stool. Image taken at 400x magnification
Figure C: Egg of O. viverrini in an unstained wet mount of concentrated stool. Image taken at 400x magnification.
Figure D: Egg of O. viverrini in an unstained wet mount of concentrated stool. Image taken at 400x magnification.
Adults of Opisthorchis spp.

 

Adults of Opisthorchis spp. are similar to, but often smaller than, Clonorchis sinensis. Adults measure approximately 7 mm long by 1.5 mm wide in the human host (adults are slightly smaller in feline hosts). Adults of Opisthorchis spp. differ from adults of Clonorchis in the shape of the testes. The distribution of the vitelline glands is also different. Both genera are similar, however, in having a ventral sucker (acetabulum) smaller than the oral sucker. Adults reside in the bile ducts of the definitive host.
Figure A: Adult of O. felineus. Image courtesy of the Web Atlas of Medical Parasitology and the Korean Society for Parasitology.
Figure B: Adult of O. viverrini. Image courtesy of the Web Atlas of Medical Parasitology and the Korean Society for Parasitology.
Intermediate hosts of Opisthorchis spp.

 

Like all trematodes, Opisthorchis spp. require a snail as an intermediate host. Snails in the genera Bithynia and Cordiella may serve as a first intermediate host for Opisthorchis spp.
Figure A: Bithynia sp., a common intermediate host of Opisthorchis spp. Image courtesy of Michal Maňas.

Laboratory Diagnosis

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

Treatment information for opisthorchis can be found at:

https://www.cdc.gov/liver-flukes/hcp/clinical-overview-opisthorchis/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/.