(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.
|(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
|| (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.
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.
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).
"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
-from American Family Physician
, June 1999.
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 -
Total Digestive Health -
Winona State University -
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
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MARKELL, JOHN, AND KROTOSKI, 1999. Medical Parasitology
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W.B. Saunders Company.
Figure 1: http://www.dpd.cdc.gov/dpdx/HTML/Clonorchiasis.htm
Figure 2: http://www.utep.edu/biology/micro/qut/csinesec.jpg
Figure 3: http://www.biosci.ohio-state.edu/~parasite/clonorchis.html
Figure 4: http://bio.winona.msus.edu/bates/Parasitology/Images/Clonorchisova.jpg
Figure 5: http://bio.winona.msus.edu/bates/Parasitology/Images/Clonorchisradiae.jpg
Figure 6: http://bio.winona.msus.edu/bates/Parasitology/Images/Clonorchiscercariae.jpg
Figure 7: http://bio.winona.msus.edu/bates/Parasitology/Images/Clonorchismetacercaria.jpg
Figure 8: http://www.biosci.ohio-state.edu/~parasite/labeled_clonorchis.html
Figure 9: http://www.dpd.cdc.gov/dpdx/HTML/Clonorchiasis.htm
Figure 10: http://www.cdfound.to.it/html/co2.htm