THE VARIED ROLES OF SNAILS - National Universities Commission

In the snail the miracidium metamorphoses into a
sporocyst, rediae, daughter rediae and cercariae.
The cercariae emerge from the snail and eneyst
on water cress, grass, barks or soil. When
ingested by a definitive host the metacercariae
exyst in the duodenum. The disease runs an acute
and chronic phases. The chronic phase occurs
when the mature fluke enters the bile duct and
symptoms pertaining to obstruction of the bile
duct or inflammation of the duct occurs.
(c) Fasciolopsiasis (Ginger worms)
This disease is caused by the parasite
Fasciolopsis buski which was earlier called
Distoma buski. The parasite is also known as the
Giant intestinal fluke of man. Its definitive hosts
are man, pig or dog.
The molluscan hosts are of the genus
Segmentina. The eggs are passed in the faeces of
the definitive hosts. These eggs hatch in 3 to 7
weeks in water having a temperature of between
80 and 90 o F to give rise to the ciliated miracidia.
These penetrate the suitable snail hosts and
develp into sporocysts, then into rediae, daughter
rediae (or rediae II) and cercariae. The cercariae
emerge from the snails and get converted into
metacercariae on the outer covering of water
chestnuts.
Human beings get infected by eating
contaminated raw water plants especially when
peeling off the outer layers with their teeth.
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