Lifecycle of Fasciola hepatica (KALBE 1998)
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Lifecycle of Fasciola hepatica (KALBE 1998) |
Fasciola hepatica is a worldwide distributed parasite of economically importance in cattle and sheep, but also man can get infected by eating raw vegetable. The adult worms live in the bile ducts and release their eggs into the lumen of the intestine. When eggs get into water the ciliated miracidia hatch after a period of 9 days up to several weeks depending on the temperature. They have to find a suitable host snail within the few hours of their live-span. After successful penetration of the intermediate host they develope through sporocyst and redial stages to cercariae, which are shedded from the snail. This free-swimming larvae attach themselves to firm surfaces like grass blades and form encysted metacercariae which are infective for several months under favourable circumstances. When ingested by the final host they excyst in the small intestine, migrate through the gut wall, cross the peritoneum and penetrate the liver capsule. After tunneling through the parenchyma for several weeks the young flukes migrate to the bile ducts and occasionally to the gall bladder and become mature.
In a comparative approach we investigate miracidial host-finding behaviour and releasing cues. Surprisingly F. hepatica miracidia show the same behavioural patterns and respond to similar macromolecular glycoconjugate signals as Schistosoma species. F. hepatica miracidia thereby distinguish their host snails from other snail species and aquatic organisms, like Trichobilharzia ocellata and some schistosome miracidia do. We are now trying to analyse the molecular basis of this species-specificity in host-finding and its role in parasite transmission under natural conditions.
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