PATHOLOGICAL EFFECT OF THE PARASITE UPON THE HOSTO. viverrini(liver fluke) occurs in N.E. Thailand and Loas and infects an estimated
7 million people. Clonorchis sinensisand O. felinusoccur in S.E. Asia, the former Soviet
Union and E. Europe. About 20 million people worldwide are infected with these flukes.
The incidence of human infection is dependent on the season, source of species and
individual fish consumed. In Thailand there is consumption of raw fish and in N.E. Laos
the descendants of Thai people also consume large amounts of raw fish.
Most children become infected by the age of ten. Some adults show intensity of egg
output with age that may reflect a continual accumulation of parasites with no immunity.
Decline in egg output over the age of 50 could be due to a change in behaviour and usage
of praziquantel. Decline in infections with age might also reflect parasite-associated
mortality. Studies of infection in hamsters indicate little evidence of immunity to the
parasite.
The observed worm burdens were found to be highly overdispersed, like most other
helminths in human communities. Using expulsive chemotherapy 11,000 Opisthorchis
worms were recovered from 246 infected residents of one village. 81% of the worms
were expelled by 25 individuals with burdens of over 100 worms. During an examina-
tion of 181 fatal accident victims, 66% of worms came from 30 heavily infected cadavers.
n 7.5. 3CHOLANGIOCARCINOMA (CANCER OF THE GALL BLADDER)
There is some evidence for a relationship between cholangiocarcinoma and the major human
liver flukes O. viverriniand C. sinenis. The mechanism of the onset of cholangiocarcinoma
has been investigated using infected hamsters. Possibly immnuocompromised, the
infected hamsters develop the disease following exposure to normally sub-carcinogenic
doses of N-nitroso-compounds or their precursors. However, with humans there may
be consumption of low levels of nitrosamines via foods preserved by bacterial fermenta-
tion (an important component of the diet) which may be the primary carcinogen lead-
ing to cholangiocarcinoma.
In response to O. viverrini, the biliary epithelium may become susceptible to malignant
transformation due to dietary carcinogens causing chronic proliferation of epithelial
cells. N-nitroso-compounds produced endogenously by activated macrophages in the
chronically inflamed biliary tract may serve as carcinogens. In fluke-infected bile duct the
activated macrophages may produce similar carcinogens.
In choliangiocarcinoma once the tumour enlarges patients become wasted and jaun-
diced and suffer a painful death, usually due to a condition known as ascending cholan-
gitis. Other biliary and gall bladder diseases such as cholangitis, obstructive jaundice,
cholelithiasis (stones in the gall bladder) and a cholecystic condition (chronic inflamma-
tion of the gall bladder) are associated with liver flukes.
Diagnosis is mainly looking through stool samples for eggs. Each worm produces
approximately 50–120 eggs/g per stool. The correlation between worm burden and
n BOX 7.1
There is a 12-fold higher frequency of this cancer in endemic areas compared to the rest
of Thailand. In western countries the incidence of liver cancers is about 2/100,000 popula-
tion whereas in Khon Kaen Province the occurrence of liver cancers is 89.2/100,000 in males
and 35.5/100,000 in females. New studies carried out using ultrasonography and stool exam-
inations show that cholangiocarcinoma may be higher in the general population than as
shown in hospital patients.