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Intestinal Trematodes 187

Disease Transmission are acquired (Figure 8-2). This discovery by Kobayashi
had the greatest impact on our knowledge of and gave a
Ingestion of uncooked or poorly cooked and encysted means for control of this infection (Cox, 2002).
vegetation such as watercress that harbor infective meta-
cercariae are capable of transmitting the infection. These
practices greatly contribute to the transmission of the or- Morphology
ganism to another host. The Chinese liver fluke, C. sinensis, produces eggs that
look somewhat delicate in design, contain a thick brown-
Laboratory Diagnosis ing shell, and prominent shoulders abutting the opercu-
lum. The egg is shaped much like a flask with a lid and is
The characteristic eggs of F. hepatica, which must be dif- similar to that of H. heterophyes and M. yokogawai. The
ferentiated from F. buski, is the best mode of identifica- eggs measure 30 μm by 15 μm and contain a fully devel-
tion of the causative organism. Clinical history is essential oped miracidium. An adult fluke ranges from 1 to 2.5 cm
in this differentiation and the Entero-test string procedure in length.
may also be helpful. The Entero-test string procedure is a
simple and non-invasive method useful in sampling duo-
denal fluid. If eggs are recovered from duodenal aspirates Symptoms
containing bile fluid, differentiation between the two spe-
Except in the cases of heavy infections by C. sinensis, the
cies may be made as F. hepatica resides exclusively in the patient is ordinarily asymptomatic and no liver damage
bile duct and the gallbladder. Serological methodology is
is evident, but heavier infections may exhibit inflamma-
also available for early diagnosis of the liver fluke infection. tory changes in the biliary epithelial tissues. Abdominal
The prognosis for an infected patient may also be tested
pain with fever and eosinophilia may occur, along with
serologically to determine if a cure has been effected. obstructive jaundice due to liver involvement and bile
duct involvement.
Treatment and Prevention

Bithinol, which is a halogenated phenol, is used for treat- Life Cycle
ment of the infection. Triclabendazole is also effective as This parasite lives almost exclusively in the liver of hu-
treatment for this parasite. Prevention of infection is ac-
mans and may also be found in large numbers in the gall-
complished by avoiding raw vegetation growing in watery bladder and bile duct and feeds on bile produced by the
environments in endemic regions. Adherence to good
liver. Such an infection can lead to complete obstruction
sanitary practices where raw human sewage is properly of the common bile duct in extreme cases. This parasite
treated and disposed of will also prevent infection.
is perhaps one of the most prevalent worm parasites in
the world and is estimated to infect up to 30,000,000
CLONORCHIS SINENSIS persons. The life cycle of Clonorchis sinensis is somewhat
similar to that of the other flukes. The egg, which con-
The human liver fluke, or Clonorchis sinensis, is a liver tains the miracidium, will float in fresh water; fresh water
fluke that is a member of the class Trematoda and is is also required for the other flukes. No further develop-
sometimes called the Chinese liver fluke. It is also a flat- ment occurs until the egg is ingested by a snail—several
worm of the phylum Platyhelminthes. The liver fluke species are capable of acting as the first intermediate host
was initially identified in 1875, but it was not until 1914 for C. sinensis. Upon reaching the digestive system of
that the snail host was first recognized by a Japanese the snail, the egg hatches, and the resultant miracidium
scientist. In 1915 a second intermediate host was dis- grows as a parasite of the snail. This miracidium devel-
covered, which further complicated the issue. The first ops into a sporocyst, which encompasses the redia, an
records of Opisthorchis infections in humans were made asexual reproductive stage. Because mating is not re-
by Konstantin Wingradoff in 1892 and the snail and fish quired, this greatly facilitates a significant increase in the
hosts and their roles in the life cycle were discovered by number of cercariae from each miracidium.
Hans Vogel in 1934. This second intermediate host was Upon maturation inside the snail, the redia bur-
an important food fish from which human infections row out of the snail’s body and inhabit the fresh water