Clonorchis sinensis by eileen ross

CLONORCHIS SINENSIS

Clonorchis sinensis - Morphology  Description:  Flat, leave-shaped trematode, body slightly elongated and slender, 15-20 mm x 3-4 mm  narrows at the anterior region into a small opening called the oral sucker, which act as the mouth while the posterior end is more broad and blunt.  From the mouth, two tubes called caeca run the length of body. They are the digestive and excretory tracts.  They are hermaphrodite ie has both male and female reproductive organs.  a single rounded ovary is at the centre of the body, and two testes are towards the posterior end.  uterus from the ovary, and seminal ducts from the testes, meet and open at the genital pore.  testes and are vitellaria are highly branched.

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Clonorchis sinensis – Egg morphology  Eggs are similar to eggs of other related flukes such as Opisthorchis  often confused during diagnosis  small and oval in shape with size measuring about 30 x 15 μm in diameter  sharply curved and with a clear convex operculum towards the narrower end  at the broader end is a stem-shaped knob  miracidium can be seen inside the fertilised egg.

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Clonorchis sinensis - Epidemiology  Also known as Chinese or Oriental liver flukes  lives in the liver of humans, and is found mainly in the common bile duct and gall bladder, feeding on bile.  They are the third most prevalent worm parasite in the world  Endemic areas include Japan, China, Taiwan and Southeast Asia  Causes infection called clonorchiasis  Signs & symptoms: jaundice, indigestion, biliary inflammation, bile obstruction, liver cirrhosis, hepatic carcinoma & cholangiocarcinoma  People become infected by eating raw or undercooked freshwater fish containing the larvae. Travelers to Asia who consume raw or undercooked fish are at risk for liver fluke infection.  Lightly salted, smoked, or pickled fish may contain infectious parasites.  Drinking river water or other nonpotable water (water is water that is not of drinking quality) will not lead to infection with Clonorchis.

LIFECYCLE (1) Embryonated eggs are discharged in the biliary ducts and in the stool. (2) Eggs are ingested by a suitable snail intermediate host. Each egg releases a miracidia (2a), which go through several developmental stage: sporocysts (2b), rediae (2c), and cercariae (2d). The cercariae are released from the snail and after a short period of free-swimming time in water, they come in contact and penetrate the flesh of freshwater fish (3), where they encyst as metacercariae (4). Infection of humans occurs by ingestion of undercooked, salted, pickled, or smoked freshwater fish. After ingestion, the metacercariae excyst in the duodenum (5) and ascend the biliary tract (6). Maturation takes approximately 1 month. In addition to humans, carnivorous animals can also serve as reservoir hosts. https://www.cdc.gov/parasites/clonorchis/biology.html#

Clonorchis sinensis – Intermediate host  The first intermediate host is always a snail  mainly Parafossarulus manchouricus  Other snail hosts include Alocinma longicornis Bithynia longicornis, Bithynia fuchsiana, Bithynia misella, Parafossarulus anomalospiralis, Melanoides tuberculata, Semisulcospira cancellata, Koreoleptoxis amurensis, Semisulcospira libertina, and Assiminea lutea in China; and Melanoides tuberculata in Vietnam.  Second intermediate host is less host-specific  The common second intermediate hosts are freshwater fish: common carp, grass carp, crucian carp, and many more. In China, 102 species of fish and four species of shrimp are known to be the intermediate hosts. In Korea, 40 species of freshwater fish are recorded as hosts. Seven species of fish are known as hosts in Russia.

Clonorchis sinensis – Diagnosis & Treatment  The usual way of diagnosing is by looking for eggs and parasite in stool sample  More than one stool sample may be needed to identify the eggs.  Stool examination is unlikely to result in a diagnosis in persons whose only exposure to Clonorchis took place more than 25–30 years ago (the life span of a liver fluke), as the liver fluke must be alive in order to produce eggs.  Additionally, cysts containing the parasite can sometimes be detected by ultrasound, CT, or MRI.  In the absence of detection of liver flukes, there is no test available that can determine if liver fluke infection is the underlying cause of cholangiocarcinoma or other liver, bile duct, or gallbladder conditions.

 Treatment: Praziquantel or albendazole

Clonorchis sinensis – Prevention & Control  Do not eat raw or undercooked freshwater fish. Lightly salted, smoked, or pickled fish can contain infectious parasites.  The FDA recommends the following for fish preparation or storage to kill any parasites.  Cooking  Cook fish adequately (to an internal temperature of at least 63°C.  Freezing (Fish)  At -20°C or below for at least 7 days or  At -35°C or below until solid, and storing at -35°C or below for at least 15 hours; or  At -35°C or below until solid and storing at -20°C or below for at least 24 hours.