Clonorchiasis is an

infectious disease An infection is the invasion of tissue (biology), tissues by pathogens, their multiplication, and the reaction of host (biology), host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmis ...

caused by the Chinese liver fluke (''Clonorchis sinensis'') and two related species. Clonorchiasis is a known risk factor for the development of cholangiocarcinoma, a

neoplasm A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...

of the biliary system. Symptoms of opisthorchiasis caused by ''Opisthorchis viverrini'' and by '' O. felineus'' are indistinguishable from clonorchiasis caused by '' Clonorchis sinensis'', leading some to argue that the disease by these three parasites should be referred to collectively as clonorchiasis..

Signs and symptoms

Cause

''Clonorchis sinensis'' is a

trematode Trematoda is a Class (biology), class of flatworms known as trematodes, and commonly as flukes. They are obligate parasite, obligate Endoparasites, internal parasites with a complex biological life cycle, life cycle requiring at least two Host ( ...

(fluke) which is part of the phylum

Platyhelminthes Platyhelminthes (from the Greek πλατύ, ''platy'', meaning "flat" and ἕλμινς (root: ἑλμινθ-), ''helminth-'', meaning "worm") is a phylum of relatively simple bilaterian, unsegmented, soft-bodied invertebrates commonly called f ...

. The parasitic worm is as long as 10 to 25 mm and lives in the bile ducts of the liver. It is a hermaphroditic fluke that requires two

intermediate host In biology and medicine, a host is a larger organism that harbours a smaller organism; whether a parasitic, a mutualistic, or a commensalist ''guest'' (symbiont). The guest is typically provided with nourishment and shelter. Examples include ...

s. The eggs of the worms are passed in fecal matter into a body of water and are then ingested by

mollusk Mollusca is a phylum of protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant species of molluscs are recognized, making it the second-largest animal phylum after Arthropoda. The ...

s. The water snail is the first intermediate host, in which a miracidium (an embryonated egg discharged in stool) goes through its developmental stages (sporocyst, rediae and cercariae).

Freshwater fish Freshwater fish are fish species that spend some or all of their lives in bodies of fresh water such as rivers, lakes, ponds and inland wetlands, where the salinity is less than 1.05%. These environments differ from marine habitats in many wa ...

are a second intermediate host for the parasitic worm. They become infected when the larva (

cercaria A cercaria (plural cercariae) is a larval form of the trematode class of parasites. It develops within the germinal cells of the Trematode life cycle stages, sporocyst or redia. A cercaria has a tapering head with large penetration glands. It may ...

) of the worm leaves the snail and penetrates the flesh of the fish. Humans then become infected by eating infected fish that has been undercooked, smoked, pickled, or salted, and from there the cycle repeats. Clonorchiasis is

endemic Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...

in the

Far East The Far East is the geographical region that encompasses the easternmost portion of the Asian continent, including North Asia, North, East Asia, East and Southeast Asia. South Asia is sometimes also included in the definition of the term. In mod ...

, especially in Korea, Japan, Taiwan, and Southern China. Clonorchiasis has been reported in areas to which it is not endemic (including the United States). In such cases, the infection follows the ingestion of undercooked or pickled freshwater fish imported from one of the endemic areas and containing

metacercariae Trematodes are parasitic flatworms of the class ''Trematoda'', specifically parasitic flukes with two Sucker (zoology), suckers: one ventral and the other Mouth, oral. Trematodes are covered by a Tegument (helminth), tegument, that protects the o ...

Diagnosis

Adult ''C. sinensis'' worms can inhabit the bile ducts of humans for 20–25 years without any clear clinical symptoms. This, in addition to the nonspecific symptoms infected persons may develop, can lead to missed diagnoses. Patients are diagnosed when ''C. sinensis'' eggs are found in stools. The formalin-ether concentration technique (FECT) method of stool examination is most effective at diagnosing light cases of infection, while the Kato-Katz (KK) method is more suitable for the diagnosing of persons with clonorchiasis. Serological methods that use enzyme-linked immunosorbent assay (ELISA) can help differentiate the eggs of ''C. sinensis'' from other flukes.

Prevention and control

The CDC recommends against eating raw, undercooked, or lightly salted, smoked, or pickled fish. The WHO recommends a combination of veterinary public health measures, education of food safety practices, and expanding access to anthelminthic drugs. The NHFPC of China has a recommendation similar to that of the WHO. Health regulators including the FDA have established requirements on the freezing of fish intended for raw consumption. The European Union (EFSA) specifically require an extended time for fish suspected of containing ''Clonorchis'' or ''Opisthorchis'' compared to other parasites. According to WHO data, larvae of these two genera are killed by freezing at for 5 days. The EFSA recommends a cooking time of 30 minutes at to kill the parasite.

Treatment

Praziquantel Praziquantel, sold under the brandname Biltricide among others, is a medication used to treat a number of types of parasitic worm infections in mammals, birds, amphibians, reptiles, and fish. In humans specifically, it is used to treat schist ...

is the treatment of choice for clonorchiasis.

References

External links

{{Helminthiases Hepatology Helminthiases Foodborne illnesses Tropical diseases