Clonorchiasis - Chinese or Oriental Liver Fluke Disease

(Trematode) Clonorchis sinensis

History of Discovery Life Cycle Clinical Presentation Transmission Reservoir
Vector Morphology Diagnostic Tests Management Therapy Epidemiology
Public Health Strategy Case Study Useful Links References Figure Listing

History of Discovery:

The Chinese liver fluke was first described by McConnell in 1874. He identified it in the bile passages of a Chinese carpenter in Calcutta. It was also found in Japan in 1875, but not described until 1883 "when Baelz attempted to differentiate a pathogenic and a nonpathogenic variety" (Craig & Faust, 580-1).

Life Cycle:

(Figure 1)In a human host, the adult worms are located in the bile ducts inside of the liver. In very severe cases, the worms can also be found in the gallbladder and pancreatic duct. The worms release eggs which pass through the feces and are ingested by freshwater snails (first intermediate host). In the intestines of the snail, the eggs release miracidia which go through several developmental stages (sporocysts, rediae, and cercariae). The free swimming cercariae exit the snail and penetrate, or encyst, as metacercariae in the flesh of freshwater fish second intermediate host). Humans become infected when they eat undercooked, salted, pickled, or smoked freshwater fish and ingest the metacercariae. The metacercariae excyst in the duodenum and the immature worms migrate to the bile duct via the ampulla of Vater. There, the worms mature and begin releasing eggs, repeating the cycle. Dogs, cats, swine, and rats can also be infected with C. sinensis.

Clinical Presentation in Humans:

In a light infection, a person is generally asymptomatic. However, if a person ingests many metacercariae over a short amount of time, there can be symptomatic early infections. In the acute phase (which lasts less than a month), fever, abdominal pain, nausea, diarrhea, anorexia, enlargement and tenderness of the liver, jaundice and eosinophilia can occur.

Chronic C. sinensis infection in childhood has been recently linked to delayed physical growth and development (Hotez, 1997).

In heavier infections(usually acquired after many years of repeated infection), functional impairment of the liver, cholangitis, cholelithiasis, pancreatitis, and cholangiocarcinoma can develop, which may be fatal.

(Figure 2) Adult worms in section of liver (Figure 3) Section of C. sinensis in the bile duct.
Note the thickening of the bile duct walls (*).


Ingestion of raw or improperly cooked freshwater fish or crayfish containing encysted larvae transmits the parasite. It is not directly transmitted from person-to-person, but an infected person may pass viable eggs up to 30 years. Transmission is most frequent in areas where human feces are used to fertilize fish ponds.


Dogs, cats, swine, rats, humans


Freshwater snail


(Fig. 4)C. sinensis eggs - released from adult worm (Fig. 5)C. sinensis radiae - in the snail intestine
(Fig. 6)C. sinensis cercariae - free-swimming (Fig. 7)C. sinensis metacercariae - encysted in fish
(Fig. 8)C. sinensis labeled adult worm found in bile duct; 10-25 mm by 3-5 mm

Diagnostic Tests:

(Figure 9) The most practical diagnostic method is microscopic observation of eggs in feces, bile, or duodenal aspirates. Eggs are 27 to 35 Ám by 11 to 20 Ám. However, the eggs of a similar parasite (Opisthorchis) are identical to C. sinensis eggs.

Serologic testing can also be helpful. Worms have been identified during surgery as well.

Management Therapy:

The preferred treatment is Praziquantel. Praziquantel is an anthelmintic that alters ion flow across the worm membrane. This change in potential causes the worm to have muscle spasms and paralysis, helping a person's immune system attack and expel the worm. When administered at 25 mg/kg three times a day for one or two days, the cure rate is about 100 per cent.

Albendazole, a benzimidazole, is also as effective when administered at 10 mg/kg twice a day for seven days. Praziquantel is preferred because it only needs to be taken for 2 days rather than the seven days for Albendazole.

In rare cases of severe biliary obstruction, surgery may be required.


(Figure 10) Endemic areas are in Asia including Korea, China, Taiwan, Japan, and Vietnam. It is estimated over 30 million people are infected with this parasite in these areas.

Clonorchiasis has been reported in non endemic areas (including the United States). In such cases, the infection is found in Asian immigrants, or following ingestion of imported, undercooked or pickled freshwater fish containing metacercariae. The freshwater snail vector is not found in the United States.

Public Health and Prevention Strategies:

According to the International Task Force for Disease Eradiation (ITFDE), "this infection is not eradicable because of the nonhuman reservoir, the many asymptomatic infections of humans, and the fact that some infected persons can shed eggs for decades." Prevalence can be reduced by promotion of sanitary disposal of human feces. Avoidance of raw fish would also reduce prevalence. However it is difficult to overcome traditional eating habits in many areas. In some endemic areas, education is directed at youth to discourage consumption of raw fish.

"In one study in Vietnam, experimental activities were conducted in two side-by-side fish ponds. In the experimental ponds, fish were cultured in conjunction with HACCP (Hazard Analysis and Critical Control Points) principles, and control pond fish were cultured according to conventional local aquaculture practices. Water supply, fish fry, fish feed, and pond conditions in the experimental pond were identified as critical control points. The HACCP principles of hazard analysis, preventative measures, critical limits, monitoring, recordkeeping, and verification procedures relating to the critical control points were applied; study results showed Clonorchis sinensis eggs and fish infected with the parasite metacercaria and the first intermediate host (Melanoides tuberculata) in the experimental ponds. Forty-five percent of control pond fish were infected with C. sinensis metacercaria, while white fish from the experimental pond monitored according to HACCP principles were completely free of trematode infection. Preliminary results indicate that application of HACCP-based principles to silver carp culture in North Vietnam is an effective way to prevent and control C. sinensis... Additional studies are recommended to confirm these preliminary results " (Garrett, Santos, and Jahncke, 1997).

Case Study:

"An 18-year-old Vietnamese woman who had arrived in the United States eight months previously was admitted with nausea, vomiting (clear emesis) and right upper quadrant and epigastric pain that alternated between being constant and colicky in character. She stated that curling into a fetal position partially relieved the abdominal pain.

On physical examination, the patient was found to have a temperature of 37.1░C (98.8░F) and right upper quadrant guarding. Some laboratory values were elevated: white blood cell count, 13,600 per mm3 (13.6 3 109 per L); serum alanine transaminase (ALT), 63 U per L; total serum bilirubin, 3.2 mg per dL (55 Ámol per L); serum alkaline phosphatase (ALP), 142 U per L; serum aspartate transaminase (AST), 112 U per L; and serum lipase, 84 U per L.

Ultrasound examination revealed a dilated common bile duct and multiple, markedly dilated tubular structures in the liver. A black, mushy, common bile duct stone was removed during endoscopic retrograde cholangiopancreatography, and intrahepatic ducts with areas of stricture and possible proximal dilatation were noted.

The patient was treated with praziquantel for a bile duct disorder that was probably caused by Clonorchis sinensis (Chinese liver fluke) infection. Her gastrointestinal symptoms responded to treatment."

-from American Family Physician, June 1999.

Useful Web Links and Web References:

Aetna Navigator Public: Praziquantel
American Family Physician
CDC Identification and Diagnosis of Parasites of Public Health Concern
CDC - Recommendations of the ITFDE
CDC - Emerging Infectious Disease
Ohio State University - Clonorchis sinensis
Total Digestive Health - Clonorchiasis
Winona State University - Biology Department


CRAIG AND FAUST, 1957. Clinical Parasitology. 6th ed. Philadelphia: Lea & Febiger.

GARRETT, SANTOS, AND JAHNCKE, "Public, Animal, and Environmental Health Implicatios of Aquaculture" Emerging Infectious Diseases. Volume 3 Number 4. October-December, 1997.

HOTEZ, ZHENG, LONG-QU, ET AL., "Emerging and Reemerging Helminthiases and the Public Health of China" Emerging Infectious Diseases. Volume 3 Number 3. July-September, 1997.

KITCHEN, "Case Studies in Internationa Medicine"American Family Physician. June, 1999.

MARKELL, JOHN, AND KROTOSKI, 1999. Medical Parasitology . 8th ed. Philadelphia: W.B. Saunders Company.

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