Vol 27 No 2 December - The Indian Society for Parasitology

74 Trematodes of public health importance
JPD : Vol. 27 (2), 2003
a patient who died in that city.
and with irrigation and with increase in the population
density of animals. The usual methods of human
Family: Schistosomatidae
exposure consist in wading, swimming, bathing or
G:- Schistosoma
washing cloths in shallow fresh water near the infected
Sps : S.bovis (cattle, sheep, goat) -portal & mesentric
snail hosts. Excreta of man and reservoir hosts
Veins.
containing viable Schistosoma eggs provide the
inoculum which initiates the extrinsic phase of the life
S. mattheei (Domestic and wild ruminants) - portal and cycle of the parasite. S. japonicum has many
mesenteric veins as well as in the veins of the mammalian reservoirs, yet the use of human faeces as
urogenital tract and stomach.
fertilizer for crops in endemic areas probably
S. intercalatum (wild and domestic ruminants , equines constitutes the most important source of infection. In
and man) - portal and mescentric veins).
certain foci in Africa baboons have been found to
maintain infection with S. mansoni with out
*S'. spindale (Ruminants & dogs ) - mesentric veins. involvement of humans (Faust et al., 1975).
S. indicum (Ruminants, equines and camels) - portal Pathogenic changes resulting from blood fluke
and mesentric veins.
infection in a susceptible host are delivered into three
S. japonicum (Man & animals) - portal & mesentric consecutive periods (1) Pre-patent period, from skin
veins).
penetration until the mature worms have arrived in the
S. mekongi (Dog & Man) - mesenteric veins.
venules of the intestine or urinary bladder and the
females are already to oviposit; (2) acute stage, which
S. nasalis (Buffaloes, cattle, sheep , goats and horses) - is one of active egg deposition and extrusion and (3)
veins of nasal mucosa.
Chronic stage, stable egg output, tissue proliferation
The eggs in faeces or urine hatch in fresh water and the
and repair.
free swimming miracidia are released. If appropriate Adult parasites cause phelibitis in the mesenteric veins
snails are found, the miracidia attack the snails soft and there is a proliferation of the tunica intima with
tissues, penetrate and transform into first generation portal or complete occlusion of the lumen. As the
sporocysts. Within each sporocyst several second - infection progresses the adult parasites shift away
generation sporocysts are developed and on escape from their predilection site in the posterior small
from the parent sporocyst migrate further into the intestine and anterior large intestines and lesions will
snail's tissues. Broad forktailed cercariae are produced be seen in other parts of the intestine as well as in other
over a period of several weeks. On maturation these organs. In addition with S. mattheei lesions in the
larvae escape from the second generation sporocysts, bladder are striking and common. Pathology of
break out of the snail and swim about in the water. bladder is seen as linear granulomata or granular
Infection of the definitive host is through active skin patches with associated haemorrhages. Adults of S.
penetration of the cercariae although cercariae may mattheei and S. indicum may in heavy infections, be
penetrate the wall of the lumen when swallowed with found in the pulmonary arteries.
water. Skin penetration is assisted by the secretions of
The hepatic syndrome is an immunological disease
the cephalic glands, which digest the tissues. Cattle
resulting from the host's cell -mediated immune
and horses may become infected when standing in the
response to Schistosome egg in the liver.
shallow water of dams, rivers, etc., during the heat of
the day. These and other animals are also infected In heavy infections the development and healing of
orally when water tanks and other source of drinking large numbers of these egg granulomas cause massive
water become infected with snails and contaminated fibrosis in the portal triads of the liver and the
with faecal material. The infection is most common in appearance of "Claypipestem" fibrosis.
man and animals where the rainfall is highest; there is a S. nasalis causes nasal granuloma (snoring disease) of
marked increase in incidence with increasing water cattle, goats and horses in India. I.H. are Lym. Luteola,
conservation (the building of small and large dams) L. accuminata and Indoplanorbis exustus. The arasites