NAME: Clonorchis sinensis
CHARACTERISTICS: Clonorchis sinensis is a trematode belonging to the Opisthorchiidae family Footnote 1Footnote 3. They are macroscopic, transparent and appear 10 to 25 mm long and 3-5 mm wide, flattened or lancet shaped flukes at the mature stage Footnote 1-3. Adult worms are characterized by a cone shaped anterior pole, a large oral sucker, and a pair of deeply lobular testes arranged one behind the other in the posterior end Footnote 1. Adult worms are able to survive in the biliary tract of their host for up to 50 years Footnote 1, where female worms discharge approximately 2000 tiny ovoid eggs every day in the fecal stream. Eggs are small, encapsulated, yellowish brown and oval with urn shaped shells with a discernible shoulder at their opercular rim and a tiny knob on the posterior pole 1-3. The eggs, 28 to 35 μm long and 12 to 19 μm wide Footnote 1, are ingested by the intermediate snail host, hatched as miracidia and metamorphosed into sporocysts and then redia. These then transform into free-swimming cercariae. Cercariae released into fresh water penetrate the tissues of fresh water fish and transform into metacercariae. When these infected fish are ingested by humans/animals, the larvae are released into the duodenum, which then migrate to the bile ducts, and can mature to adulthood within 30 days Footnote 1.
PATHOGENICITY/TOXICITY: There is consensus that the biology and pathologic characteristics of Opisthorchis and Clonorchis are the same. C. sinensis resides in the bile ducts of hosts where it causes inflammatory and proliferative alterations Footnote 2.Light infections (100 flukes) may be asymptomatic, but heavy infections can result in severe disease Footnote 3. Symptoms of light infections are generally mild such as fatigue, loss of appetite, nausea, diarrhea and the sensation of abdominal pressure or pain, hepatomegaly, fever, icterus, and occasionally urticaria 2Footnote 4. Heavy worm loads (> than 1000 flukes) observed in persistent/chronic infections may cause dizziness, tremors, convulsions, loss of weight and developmental abnormalities in children Footnote 2. Persistent/chronic infections may also cause liver cirrhosis, edema, cholecystitis, obstructive jaundice, hepatomegaly, multiple hepatic tumors and ascites 2Footnote 4. Obstruction of the bile duct with dead worms, although rare, can result in bacterial cholangitis, accompanied by bacteremia, endotoxin shock, and hypoglycemia 1Footnote 2. Adult worms may also occasionally cause infection of the pancreatic ducts (acute pancreatitis) Footnote 1Footnote 2Footnote 4. Chlonorchiasis is considered a major risk factor for the development of cholangiocarcinoma Footnote 1Footnote 2Footnote 4.
EPIDEMIOLOGY: Chlonorchiasis is prevalent in all Asian countries Footnote 2. It is endemic in East Asian countries, including China, South Korea, Japan, Taiwan, northern Vietnam and far eastern RussiaFootnote 1Footnote 2Footnote 4Footnote 5. Approximately 35 million people have been estimated to be infected by C. sinensis, globally, with 15 million people infected in China Footnote 5. No outbreaks of the disease have been reported from Japan since 1991Footnote 5. Korea and Vietnam have an estimated prevalence rate of 1.4% and 5.3–28.4%, respectively Footnote 5. The incidence of clonorchiasis has been reported to be higher among fishermen, fishmongers, workers processing fish products, because of undesirable working and eating habits Footnote 5. Clonorchiasis has also been reported among Asian immigrants to North America with prevalence rates of approximately 26% Footnote 5.
HOST RANGE: Humans, dogs, pigs, and various small carnivores such as martens and rats Footnote 1Footnote 2Footnote 5. Snails (A. longicornis, P. striatulus, and B. fuchsianus) and fresh water fish or shrimp serve as intermediate hosts for infection in mammals Footnote 1Footnote 2Footnote 5.
INFECTIOUS DOSE: Unknown.
MODE OF TRANSMISSION: Clonorchiasis is acquired by ingestion of raw, frozen, dried, salted, smoked or pickled fish. The most important fish species, mainly carp, are Cyprinus carpi, Pseudorasbora parva, Ctenopharyngodon idellus, Leucogobia guntheri, Carassius spp. and Hemilculter spp., or shrimp containing encysted metacercariae larvae Footnote 1Footnote 2Footnote 5.
INCUBATION PERIOD: Unknown.
COMMUNICABILITY: Not transmitted from human-to-human.
RESERVOIR: Mammals, such as cats, dogs, foxes, mink, pigs, rodents, and possibly other fish eating mammals Footnote 5.
DRUG SUSCEPTIBILITY: Susceptible to tribendimidine (TBD), praziquantel, artemether and artesunate Footnote 6-8. Albendazole has produced cure rates of 93% to 100% Footnote 9 Footnote 10. Although some studies have suggested that it may not be as effective as praziquantel.
DRUG RESISTANCE: Although no resistance has been reported for praziquantel, low success (29%) of treatment with this drug was reported from one study in Vietnam Footnote 6.
SUSCEPTIBILITY TO DISINFECTANTS: Information on disinfection specific to C. sinensis is not available. Zhang et al. (2003) demonstrated that 2 g N/l of ammonium bicarbonate can reduce the viability of C. sinensis metacercariae Footnote 11. Similar organisms have been shown to be susceptible to 1000-5000 ppm sodium hypochlorite, formaldehyde – most effective at above 20°C Footnote 12, and 2% glutaraldehyde.
SURVIVAL OUTSIDE HOST: Clonorchis sinensis can survive in cold temperatures (4°C) in either PBS or in saline solution for up to six months and, although alive, may not sustain all levels of viability and infectivity Footnote 15.
SURVEILLANCE: Monitor for clinical symptoms Footnote 1. Ultrasound imaging can be used to detect intrahepatic duct dilatation, periductal echogenicity and gallbladder sludge Footnote 4. Magnetic resonance imaging (MRI) or computed tomography (CT) can also be used for detecting subtle cases of cholangiocarcinoma Footnote 5. Recovery followed by count and microscopic identification of C. simensis eggs from clinical specimens such as feces or biliary tract fluid can confirm the presence of worms in the biliary tract. Three techniques are currently used for identification of C. sinensis from feces: Kato-Katz (KK) method, formalin-ether concentration technique (FECT) and direct smear Footnote 4 Footnote 16. Examination of multiple stool specimens may be necessary in lighter infections, but in infections of less than 20 adult flukes, no eggs may be found Footnote 1. ERCP with biliary tract sampling is the most sensitive method of detectionFootnote 17.
Serological tests such as ELISA for the detection of C. sinensis cysteine protease protein, or Dot-ELISA for detection of circulating antigen (CAg) can also be effective in confirming infection Footnote 2 Footnote 4 Footnote 18. Infection can be confirmed using PCR Footnote 19.
Note: All diagnostic methods may not be available in all countries.
FIRST AID/TREATMENT: Chlonorchiasisis treated withoral praziquantel or oral albendazole Footnote 1-4 Footnote 7. Surgical removal of the pathogen and infected tissue is also done for severe cases Footnote 5.
LABORATORY-ACQUIRED INFECTIONS: None reported.
SOURCE/SPECIMENS: Feces, or duodenal aspirates Footnote 1.
PRIMARY HAZARDS: Ingestion of eggs Footnote 1.
SPECIAL HAZARDS: None.
RISK GROUP CLASSIFICATION: Risk Group 2 Footnote 20.
CONTAINMENT REQUIREMENTS: Containment Level 2 facilities, equipment, and operational practices for work involving infectious or potentially infectious materials, animals, or cultures.
PROTECTIVE CLOTHING: Lab coat. Gloves when direct skin contact with infected materials or animals is unavoidable. Eye protection must be used where there is a known or potential risk of exposure to splashes Footnote 21.
OTHER PRECAUTIONS: All procedures that may produce aerosols, or involve high concentrations or large volumes should be conducted in a biological safety cabinet (BSC). The use of needles, syringes, and other sharp objects should be strictly limited. Additional precautions should be considered with work involving animals or large scale activities Footnote 21.
SPILLS: Allow aerosols to settle and, wearing protective clothing, gently cover spill with paper towels and apply an appropriate disinfectant, starting at the perimeter and working towards the centre. Allow sufficient contact time before clean up Footnote 21.
DISPOSAL: Decontaminate all wastes that contain or have come in contact with the infectious organism before disposing by autoclave, chemical disinfection, gamma irradiation, or incineration Footnote 21.
STORAGE The infectious agent should be stored in leak-proof containers that are appropriately labelled Footnote 21. Studies have found that C. sinensis stored in cold (4°C) PBS with antibiotics refreshed monthly resulted in best levels of sustained viability and infectivity Footnote 15.
REGULATORY INFORMATION: The import, transport, and use of pathogens in Canada is regulated under many regulatory bodies, including the Public Health Agency of Canada, Health Canada, Canadian Food Inspection Agency, Environment Canada, and Transport Canada. Users are responsible for ensuring they are compliant with all relevant acts, regulations, guidelines, and standards.
UPDATED: December 2011
PREPARED BY: Pathogen Regulation Directorate, Public Health Agency of Canada
Although the information, opinions and recommendations contained in this Pathogen Safety Data sheet are compiled from sources believed to be reliable, we accept no responsibility for the accuracy, sufficiency, or reliability or for any loss or injury resulting from the use of the information. Newly discovered hazards are frequent and this information may not be completely up to date.
Copyright © Public Health Agency of Canada, 2011 Canada