Vol 27 No 2 December - The Indian Society for Parasitology

72 Trematodes of public health importance
JPD : Vol. 27 (2), 2003
cone, slightly larger acetabulum, more anterior
position of the testes and large size of the eggs. The
natural hosts are cattle, buffaloes, sheep and other
herbivorous mammals. The life cycle parallels that of
F. hepatica, including Lymnaeid snails as 1st I.H.
Clinical aspects of this infection are essentially the
same as in fasciolisis due to F. hepatica. Human
infections have been reported from Senegambia, (West
Africa) Vietnam, Tashkant, Iraq and Hawai.
Dicrocoelium dendriticum
D. dendriticum is a common parasite of bile passage of
sheep and other herbivorous mammals in Europe,
North Africa, Northern Asia and to a lesser extent in
North and South America. Numerous cases of human
infection have been reported from the USSR and else
where. Most of these are cases of false parasites is
resulting from consumption of infected livers with the
evacuation of eggs of D. dendriticum in the consumer's
faeces, but genuine human cases have been diagnosed
from Europe, Asia and Africa. The adult worm is of
lancet shaped and resides in the bile ducts of sheep,
goats, cattle, pigs, horse, dog and rarely in man. The
infection is endemic in hilly areas in India. The 1st I.H.
are terrestrial gastropods (Macrochlamys species in
India, Labrina, Hellicella and Cionella species in other
countries 2nd I.H. is ant (Formica fusca) Cercariae
(Xiphido type) clump together in masses by sticky
substance (Slime balls) in the pulmonary chamber of
the snails and are expelled to adhere the vegetation.
These are swallowed by ants. Metacercariae develop
nd
in the ants. The 2 I.H. is necessary for the completion
of the lifecycle. Definitive host gets infection by
ingesting infected ants. Immature flukes after
excystment penetrate into the intestinal wall of the
final host, pass by the portal circulation to the liver and
eventually enter the bile ducts.
The young flukes develop in the smaller bile ducts, the
old ones go to the longer bile ducts. They are fully
grown after 7 weeks and the first eggs are laid 4 weeks
later.
Distomiasis is not so pathogenic as Fasciola but in
advanced infection there is extensive cirrhosis and bile
ducts are markedly distended due to large number of
flukes. The clinical picture in severe cases consists of
anaemia, oedema and emaciation. (Hafeez 1993)
Clonorchis sinensis
C.sinensis, the Chinese liver fluke; was first reported
from the bile passages of a Chinese carpenter who was
antopsied in Calcutta. It was reported from Japan in
1883 and from South China in 1908. The endemic
enzootic area of C.sinensis extends from Japan to
Vietnam. The incidence is related to eating raw fish. In
South China eggs of C. sinensis are found in the stools
of over 10 percent of the population. In central China
75 to 100% of cats and dogs are infected, but the
incidence of human infection is low. In Japan human
infection was 6 to 40 percent. Adult parasites are found
in a biliary tract of the man, cat, pig, rat, mouse, camel,
etc. 1st snail I.H.: Parafossarulus manchourius in
China, Formosa, Indo-China, Korea and Japan,
Bulinus (Bithynia) Fuchsianus in S. China, Alocinma
nd
longicomis in China. 2 I.H.: Fresh water fish. The
cercariae released from the snail encyst on fresh water
fishes. The infected uncooked fish on being eaten, the
metacercariae excyst in the duodenum, migrate
through the biliary passage make their way into
ampulla of water to the smaller bile radicals and finally
to the distal biliary passages, settle soon in liver and
mature in one month. Each worm passes 2400 eggs
daily.
Mature C. sinensis in the bile passages provoke
marked hyperplasia of the biliary epithelium with
subsequent dense fibrosis and encapsulation of the
duct. As the number of worms increase, there is
increase in lumial diameter of all the terminal bile
ducts resulting in fibrous thickening of the walls and
pressure necrosis of adjacent hepatic parenchyma.
The clinical onset may be gradual, or sudden with
chills and fever. The liver becomes large and tender. In
some cases there may be congestive splenomegaly
followed by hepatitis and eosinophilia of 10-40
percent.
Opisthorchis felineus
0. felineus (synonym of 0. tenuicollis) was originally
described from a cat in Italy and a few years later from
a man in Siberia. It has a wide distribution in Eastern
and South Eastern Europe and Asiatic USSR. It is
reported commonly in Vietnam and has been
recovered from humans in Japan and India. It inhabits
the distal biliary and pancreatic tracts of cat, dog, fox,