Life Cycle

The life cycles of , Fasciolopsis and Echinostoma 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  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.  Infection with Echinostoma species is thought to be contracted by injestion of fresh water snails containing metacercaria.

Morphology of ova

Ova of  Fasciolopsis and Echinostoma species are all thin shelled, ellipsoid bile stained ova with an operculum that is often inconspicuous.  Although ova of Echinostoma species can usually be differentiated by size, there is much crossover in the size of Fasciola and Fasciolopsis species.

Pathogenesis

The adult flukes of Fasciolopsis buski attach to the intestine, resulting in local inflammation and ulceration.  Heavier infections may subsequently lead to abdominal pain, malabsorption and persistent diarrhoea.  Marked eosinophilia may be seen.

The adult flukes of Echinostoma species attach to the intestine resulting in little damage to the intestinal mucosa..  Light infections are generally asymptomatic and heavy infections may produce light ulceration, diarrhoea and abdominal pain..

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.

A Summary of the less common intestinal flukes