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Opisthorchiasis

[Onchocerca volvulus[Opisthorchis felineus] [Opisthorchis viverrini]

Causal Agents

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


Life Cycle

Lifecycle

The adult flukes deposit fully developed eggs that are passed in the fecesThe number 1. After ingestion by a suitable snail (first intermediate host)The number 2, the eggs release miracidiaThe number 2a , which undergo in the snail several developmental stages (sporocystsThe number 2b, rediaeThe number 2c, cercariaeThe number 2d ). Cercariae are released from the snailThe number 3 and penetrate freshwater fish (second intermediate host), encysting as metacercariae in the muscles or under the scalesThe 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 duodenumThe 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 weeksThe 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, and Kampuchea. Opisthorchis felineus is found mainly in Europe and Asia, including the former Soviet Union.

Clinical Presentation

Most infections are asymptomatic. 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

Figure A: Egg of O. viverrini in an unstained wet mount of concentrated stool. Image taken at 400x magnification.

	Figure B

Figure B: Egg of O. viverrini in an unstained wet mount of concentrated stool. Image taken at 400x magnification

	Figure C

Figure C: Egg of O. viverrini in an unstained wet mount of concentrated stool. Image taken at 400x magnification.

	Figure D

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

Figure A: Adult of O. felineus. Image courtesy of the Web Atlas of Medical Parasitology and the Korean Society for Parasitology.

	Figure B

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

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.

Treatment Information

Praziquantel, adults, 75mg/kg/day orally, three doses per day for 2 days; the pediatric dosage is the same. Praziquantel should be taken with liquids during meals.

Alternative:

Albendazole* is an alternative drug; the dosage is 10mg/kg/day for 7 days. The pediatric dosage is the same. Albendazole should be taken with food; a fatty meal increases the bioavailablility.

* Not FDA-approved for this indication

Praziquantel

Oral praziquantel is available for human use in the United States.

Praziquantel is pregnancy category B. There are no adequate and well-controlled studies in pregnant women. However, the available evidence suggests no difference in adverse birth outcomes in the children of women who were accidentally treated with praziquantel during mass prevention campaigns compared with those who were not. In mass prevention campaigns for which the World Health Organization (WHO) has determined that the benefit of treatment outweighs the risk, WHO encourages the use of praziquantel in any stage of pregnancy. For individual patients in clinical settings, the risk of treatment in pregnant women who are known to have an infection needs to be balanced with the risk of disease progression in the absence of treatment.

Pregnancy Category B: Either animal-reproduction studies have not demonstrated a fetal risk but there are no controlled studies in pregnant women or animal-reproduction studies have shown an adverse effect (other than a decrease in fertility) that was not confirmed in controlled studies in women in the first trimester (and there is no evidence of a risk in later trimesters).

Praziquantel is excreted in low concentrations in human milk. According to WHO guidelines for mass prevention campaigns, the use of praziquantel during lactation is encouraged. For individual patients in clinical settings, praziquantel should be used in breast-feeding women only when the risk to the infant is outweighed by the risk of disease progress in the mother in the absence of treatment.

The safety of praziquantel in children aged less than 4 years has not been established. Many children younger than 4 years old have been treated without reported adverse effects in mass prevention campaigns and in studies of schistosomiasis. For individual patients in clinical settings, the risk of treatment of children younger than 4 years old who are known to have an infection needs to be balanced with the risk of disease progression in the absence of treatment.

Albendazole

Oral albendazole is available for human use in the United States.

Albendazole is pregnancy category C. Data on the use of albendazole in pregnant women are limited, though the available evidence suggests no difference in congenital abnormalities in the children of women who were accidentally treated with albendazole during mass prevention campaigns compared with those who were not. In mass prevention campaigns for which the World Health Organization (WHO) has determined that the benefit of treatment outweighs the risk, WHO allows use of albendazole in the 2nd and 3rd trimesters of pregnancy. However, the risk of treatment in pregnant women who are known to have an infection needs to be balanced with the risk of disease progression in the absence of treatment.

Pregnancy Category C: Either studies in animals have revealed adverse effects on the fetus (teratogenic or embryocidal, or other) and there are no controlled studies in women or studies in women and animals are not available. Drugs should be given only if the potential benefit justifies the potential risk to the fetus.

It is not known whether albendazole is excreted in human milk. Albendazole should be used with caution in breastfeeding women.

The safety of albendazole in children less than 6 years old is not certain. Studies of the use of albendazole in children as young as one year old suggest that its use is safe. According to WHO guidelines for mass prevention campaigns, albendazole can be used in children as young as 1 year old. Many children less than 6 years old have been treated in these campaigns with albendazole, albeit at a reduced dose.

References
  • Soukhathammavong P, Odermatt P, Sayasone S, Vonghachack Y, Vounatsou P, Hatz C, Akkhavong K, Keiser J. Efficacy and safety of mefloquine, artesunate, mefloquine-artesunate, tribendimidine, and praziquantel in patients with Opisthorchis viverrini: a randomised, exploratory, open-label, phase 2 trial. Lancet Infect Dis 2011;11:110-8.
  • Keiser J, Utzinger J. The drugs we have and the drugs we need against major helminth infections. Adv Parasitol 2010;73:197-230.
  • Keiser J, Utzinger J. Food-borne tremadodiases. Clin Microbiol Rev 2009;22:466-83.
  • Keiser J, Utzinger J. Food-borne trematodiasis: current chemotherapy and advances with artemisinins and synthetic trioxolanes. Trends Parasitol 2007;23:605-12.
  • Jong EC, Wasserheit JN, Johnson RJ, Carberry WL, Agosti J, Dunning S, Clark H. Praziquantel for the treatment of Clonorchis/Opisthorchis infections: report of a double-blind, placebo-controlled trial. J Infect Dis 1985;152:637-40.

 

 

 

 

 

 

 

DPDx is an education resource designed for health professionals and laboratory scientists. For an overview including prevention and control visit www.cdc.gov/parasites/.

  • Page last reviewed: May 3, 2016
  • Page last updated: May 3, 2016
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