Clonorchis sinensis
By Thanh Tran and Dhool Mohamud
Taxonomy
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Kingdom: Animalia
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Phylum: Platyhelminthes
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Class: Trematoda
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Order: Opisthorchiida
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Family: Opisthorchiidae
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Genus: Clonorchis
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Species: Sinensis
Clonorochis sinensis
(Branched testes)
Introduction
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Opisthorchis sinensis (lobed)
Common Name: Oriental liver fluke, Chinese
liver fluke
Lives: in the liver of humans, and is found
mainly in the common bile ducts and gall
bladder.
Disease: Clonorchiasis
Clonorochis sinensis was first discovered by
McConnell in 1875 in the bile passage of a
Chinese carpenter in Calcutta.
Clonorochis was formally known as
Opisthorchis sinensis, however it 1907, Looss
erected the genus Clonorochis because of
the branched testes in contrast to the lobed
testes of Opisthorchis.
Hosts
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First intermediate host: Freshwater
snail (Parafossarulus manchouricus)
Occurrences Outside of Asia
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Second intermediate host: Fish (most
commonly Grass carp)
Definitive host: Humans, pigs, dogs,
cats, rats, camels,
Reservoir host: dogs, cats
Geographic distribution: Japan,
Korea, Taiwan, China, and Vietnam
Currently infecting an estimated
30,000,000 humans.
Believed to be the third most
prevalent worm parasite in the
world
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Clonorchiasis has been reported in non
endemic areas (including the United
States). In such cases, the infection was
found in Asian immigrants, or individuals
who have ingested pickled freshwater fish
containing metacercariae imported from
endemic areas.
The freshwater snail vector is not found in
the United States
Morphology
sinensis radiae - in the snail intestine
Miracidium - This larval stage is ciliated and slightly oval in
shape. It has 2 simple eyespots and lateral papillae which
protrude outwards and serve as sensory organs.
Sporocyst- The sporocyst resembles a hollow and simple sac.
Rediae -It has a pharynx but no esophagus or intestine.
sinensis eggs - released from adult
worm
Cercaria - resembles a small adult with a tail, which it loses
upon penetration of the second intermediate host. The tail has
dorsal and ventral fins on it to aid in locomotion. It is brownish
in color
Metacercaria - is encysted and does not look like a fluke. It
has lost larval organs such as the eyespots, the stylet, and the
tail. The cyst has thick walls and maturing fluke is visible
sinensis cercariae - free-swimming
sinensis metacercariae - encysted
in fish
Anatomy of Adult Fluke
The adult worm measures to be 8-25 mm
long and 1.5-5.0 mm wide. The oral sucker
is slightly larger than the ventral oral sucker.
The male reproductive organs consists of two
large branched testes in the posterior end.
The ovary consists of three lobes. The adult C.
sinensis do not have a body cavity, blood
circulatory system, scales or spine. The Fluke
can be translucent gray or yellow due to the
absorption of bile.
Life Cycle
Behavioral pattern: The cercaria emerges
from the snail, and positions itself in an
upside-down position, and sinks towards
the bottom of the water. Though the exact
way a C. sinensis cercaria sense stimuli is
unknown, it is stimulated to swim by
passing shadows and movement in the
water. Any kind of stimulation will cause it
to swim rapidly back up and then resumes
its sinking,. This behavioral pattern favors
its contact with another host. On touching
the epithelium of the fish it attaches itself,
castes its tail and bores through the skin.
Life Cycle
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Embryonated eggs are discharged in the billiary ducts and in
the stool
Eggs are ingested by a suitable snail intermediate host . Each
egg releases a miracidia , which go through several
developmental stages (sporocysts , rediae , and cercariae ).
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, where they encyst as
metacercariae
Infection of humans occurs by ingestion of undercooked, salted,
pickled, or smoked freshwater fish
After ingestion, the metacercariae excyst in the duodenum and
ascend the biliary tract through the ampulla of Vater
Maturation takes approximately 1 month. The adult flukes
(measuring 10 to 25 mm by 3 to 5 mm) reside in small and
medium sized biliary ducts. In addition to humans, carnivorous
animals can serve as reservoir hosts.
Symptoms
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In the second-order bile ducts, the flukes can
cause erosion of epithelium lining.
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Excessive mucus production
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inflammation
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Epithelial cell proliferation
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Periductal fibrosis and necrosis
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Atrophy of surrounding liver cells
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In the acute phase, abdominal pain, nausea,
diarrhea, and eosinophilia can occur
Adult metacercaria may consume all the bile
created in the liver (individual is unable to
digest fats) causing obstruction of the biliary
ducts.
flukes (arrows) within the dilated bile ducts
Clinical Diagnosis
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The most practical diagnostic method is
microscopic observation of eggs in feces, bile,
or duodenal aspirates.
Computed Tomographic scan (CT) of the
abdomen, and shows dilated common bile duct
Treatment
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Triclabenzole, praziquantel, bithionol, albendazole,
mebendazole
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% effective.
Albendazole is also as effective when administered
at 10 mg/kg twice a day for seven days.
Public Health and Prevention
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The infection is not eradicable because of
diversity and large numbers of nonhuman
reservoirs.
Many of the infected humans are asymptomatic
and 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.
Cantonese delicacy of raw carp, rice soup and soysauce
Interesting Facts
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Adult liver flukes can produce up to 4000 eggs
per day for at least six months.
Worms can live up to 8 years in humans.
An infected person may pass viable eggs up to
30 years.
The redia is the first stage that actually feeds.
It feeds actively on the tissues of the first
intermediate host, normally the digestive and
reproductive systems.
A human host with an average infection will
have two or three dozen worms; heavily
infected individuals have been found with as
many as 20,000 worms.
Video
References
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"Clonorchis Sinensis." Wikipedia, the Free Encyclopedia. Web. 20 Feb. 2011.
<http://en.wikipedia.org/wiki/Clonorchis_sinensis>.
"Clonorchiasis Site." Stanford University. Web. 20 Feb. 2011.
<http://www.stanford.edu/group/parasites/ParaSites2001/clonorch/ClonorchiasisWebsite.html>.
Eckroad, E. and H. Lee. 2001. "Clonorchis sinensis" (On-line), Animal Diversity Web. Accessed February 20,
2011 http://animaldiversity.ummz.umich.edu/site/accounts/information/Clonorchis_sinensis.html
Roberts, Larry S., Gerald D. Schmidt, and John Janovy. Gerald D. Schmidt & Larry S. Roberts' Foundations of
Parasitology. Boston: McGraw-Hill Higher Education, 2009.