Page 151 - Medical Parasitology_ A Textbook ( PDFDrive )

144 12 Trematodes: Flukes

Prevention and Control
1. Proper cooking of freshwater fish
2. Proper disposal of faeces
3. Control of snails
4. Treatment of cases

Opisthorchis viverrini

Its infection is usually asymptomatic but may sometimes resemble clonorchiasis.
Opisthorchis viverrini is common in Thailand and is associated with cholangiocar-
cinoma. The life cycle and other features of Opisthorchis are similar to Clonorchis.
Adult worm of Opisthorchis has lobe-shaped testes. The egg is similar in morphol-
ogy to that of Clonorchis. Praziquantel (75 mg/kg/day orally, 3 doses per day for 2
days) is the drug of choice.

Fasciola hepatica

Common name Sheep liver fluke

Distribution
It is worldwide in distribution, being found mainly in sheep-rearing countries.

Habitat
The parasite resides in the liver and biliary passages of the definitive host.

Morphology
The adult worm is large, leaf-shaped fleshy fluke, measuring 30 mm long and
15 mm broad. It has a conical projection anteriorly with an oral sucker and is
rounded posteriorly. It is a hermaphrodite.
Its eggs are large, ovoid, operculated, measuring 140 μm by 80 μm in size
(Fig. 12.7). Eggs are unembryonated when passed in faeces. Eggs of Fasciola
hepatica and Fasciolopsis buski (intestinal fluke) cannot be differentiated.

Life Cycle (Fig. 12.8)
(1) Unembryonated eggs are passed in faeces of infected human, sheep or cattle. (2)
The eggs embryonate in water. (3) Miracidia hatch and penetrate freshwater snail.
(4) In the snail, they undergo development to the cercarial stage. (5) The free swim-
ming cercariae encyst on water plants. (6) The metacercariae on water plants are
ingested by human, sheep or cattle. (7–8) The metacercariae excyst in the duode-
num and develop into adults in hepatic biliary ducts.