The liver and intestinal trematodes are leaf shaped and are hermaphroditic.  They have a similar life cycle and humans become infected by ingesting undercooked vegetation or fish

Life cycle

Introduction

Fasciolaspecies are trematodes which parasitise a variety of vertebrates.  They are hermaphroditic and their di

	Fasciola hepatica	Fasciola gigantica
Geographic distribution	Cosmopolitan	Africa, the Orient and Hawaiian islands
Reservoir hosts	Sheep	camels, cattle and water buffalo
Location of adult in host	Bile ducts	Bile ducts
Size of ova	130 - 150 by 63 - 90	160 - 190 by 70 - 90

stinguishing characteristics are shown in the following table.

The life cycles of Fasciola species are complex, requiring more than one intermediate host.  The first intermediate host is the snail in which the miracidia undergo a complex series of development, ultimately resulting in the liberation of large numbers of larvae known as cercariae.  The cercariae of Fasciola and Fasciolopsis become attached to water vegetation and form a resistant cyst wall.  These stages are known as metacercariae and they remain on the vegetation until ingestion. 

Morphology of ova

Ova of Fasciola species are all thin shelled, ellipsoid bile stained ova with an operculum that is often inconspicuous. 

Pathogenesis

Light infections due to Fasciola hepatica may be asymptomatic.  However, they may produce cholangitis.  Epigastric pain and nausea may also occur.

Infections due to Fasciola gigantica occur mainly in cattle raising areas and cause clinical symptoms similar to those of Fasciola hepatica although human infections are less common.

Laboratory diagnosis

Definitive diagnosis is made by observing the ova in faeces.  Where identification cannot be made from the size of the ova, clinical information and the source of infection may help to provide a diagnosis.  Serological techniques are available for the diagnosis of Fasciola hepatica.

Clonorchis sinensis

Introduction

Clonorchis sinensis, also known as the Chinese liver fluke is a narrow elongate liver fluke found in the Far East.  It parasitises the biliary duct in humans who become infected by eating raw or undercooked fish.  Dogs and cats are the most important reservoir hosts.

Morphology of ova

The ova of Clonorchis sinensis contain fully developed miracidia and possess prominent opercular shoulders.  They are bile stained and measure29m by 16m. 

An ovum of Clonorchis sinensis

An ovum displaying size

Pathogenesis

Light infections are usually asymptomatic.  Acute infections may be characterised by fever, diarrhoea, epigastric pain, enlargement and tenderness of liver and sometimes jaundice.  The invasion by these worms in the gallbladder may cause cholecystitis.

Laboratory diagnosis

Definitive diagnosis is made by observing the characteristic ova in faeces or from duodenal aspirates or from the Entero-Test.

A Summary of the less common liver flukes

	Opisthorchis viverreni	Dicrocoelium dendriticum
Geographic distribution	Thailand	Far East
Location of adult in host	Liver and bile ducts	Liver and bile ducts
Size of ova	26.7 by 15m	38 – 45m by    22 - 30m
Shape of ova	Prominent opercular shoulders Bile stained	Dark brown, thick shelled and large operculum
Infection acquired by	Eating raw fresh water fish	Eating infected ants
Symptoms	Malaise and right upper quadrant pain	Biliary and digestive problems