THE VARIED ROLES OF SNAILS - National Universities Commission

other parasitic infections the snail borne worms do not
directly replicate inside the body but rather produce
copious amounts of eggs. It is these eggs, which depending
on the species of worms that are voided into the
environment through sputum, urine or faeces, facilitating
the life cycles of the parasites.
The eggs that fail to exit the body often become trapped in
host tissues and organs and ultimately trigger the
immunopathology associated with the disease.
(b) Fascioliasis
Another name for this disease is liver fluke
disease. This disease is caused by the infection
with the trematode Fasciola (F. hepatica and F.
gigantica). The source of infection is ingestion of
raw aquatic vegetation contaminated with
encysted metacercariae such as lettuce and green
salad, grasses and water crests.
Fasciola passes its life cycle in two different
hosts: sheap, goat and cattle are the definitive
hosts which snails of the genus Lymnaea are the
intermediate hosts. The undifferentiated ovum
develops into a miracidium under moist
conditions in 9 – 15 days at 22 – 25 o C. The
miracidiae which hatch out of the eggs lives for
only eight hours and can move in a film of
moisture on damp pastures. Further development
takes place after free living miracidium
penetrates an amphibious snail. More than 20
species of Lymnaea have been incriminated as
capable of acting as intermediate host for
Fasciola.
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