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Effect of praziquantel on the free-living stages ofSchistosoma mansoni

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The effect of the new schistosomicide praziquantel (2-cyclohexyl-carbonyl-1,2,3,6,7,11b-hexahydro-2H-pyrazino[2,1a]isoquinolin-4-one) on the miracidia and cercariae ofSchistosoma mansoni was investigated.

In vivo praziquantel inhibits hatching of miracidia for 24 h after administration of 500 mg/kg to infected mice. In vitro a concentration of 10 μg/ml inhibits subsequent hatching in drug-free water. Free swimming miracidia are rapidly killed by 1 μg/ml. Even 0.01 μg/ml is still partially effective.

In a solution of 0.03 μg/ml cercariae lose their ability to swim within 10 min. This effect is reversible in drug-free water. Morphological damage to cercariae incubated in 0.1 μg/ml is clearly evident. However, cercariae are fully infective when given subcutaneously to mice after a 3-h incubation period. Incubation in 1 μg/ml reduces the infection rate by 80%. A 2-h incubation in 0.1 μg/ml almost completely inhibits the percutaneous infection through the abdominal skin. The number of cercariae that develop to schistosomules is reduced by more than 90%. After a 2-h incubation in a concentration of 0.01 μg/ml the swimming ability of cercariae is impaired in such a way that the number of cercariae penetrating in the tail immersion test and developing to schistosomules is reduced by half.

Praziquantel is a more potent protective agent than the molluscicides copper sulphate, sodium pentachlorophenate and Bayluscide® or cadmium and zinc ions.


Es wurde der Einfluß des neuen Schistosomenmittels Praziquantel (2-Cyclohexylcarbonyl-1,2,3,6,7,11b-hexahydro-2H-pyrazino[2,1 a]isochinolin-4-on) auf die Miracidien und Cercarien vonSchistosoma mansoni untersucht.

In vivo verhindert Praziquatel das Schlüpfen von Miracidien aus Eiern für 24 h nach einer Behandlung infizierter Mäuse mit 500 mg/kg. Nach Inkubation von Eiern in 10 μg/ml schlüpfen anschließend keine Miracidien in präparatfreiem Wasser. Frei schwimmende Miracidien werden durch 1 μg/ml schnell abgetötet und noch 0,01 μg/ml haben eine deutliche Wirkung.

Cercarien werden in vitro durch 0,03 μg/ml innerhalb von 10 min schwimmunfähig. Dieser Effekt ist in präparatfreiem Wasser reversibel. Nach 3stündiger Vorbehandlung in 0,1 μg/ml sind die Cercarien deutlich morphologisch geschädigt. Trotzdem sind sie noch normal entwicklungsfähig, wenn sie Mäusen subcutan injiziert werden. Nach Inkubation in 1 μg/ml ist der Infektionserfolg allerdings um 80% reduziert. Nach nur 2stündiger Inkubation in 0,1 μg/ml ist die Zahl der Cercarien, die sich nach percutaner Infektion durch die Bauchhaut der Maus zu Schistosomulae entwickelt, um mehr als 90% reduziert. Nach 2stündiger Inkubation in nur 0,01 μg/ml ist das Schwimmvermögen der Cercarien so beeinträchtigt, daß sich nach percutaner Schwanzinfektion nur noch halb so viele zu Schistosomulae entwickeln wie in der Kontrolle.

Praziquantel ist in seiner infektionsverhindernden Wirkung den Molluskiziden Kupfersulfat, Pentachlorphenolnatrium und Bayluscid® sowie auch Cadmium- und Zinkionen überlegen.

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Andrews, P. Effect of praziquantel on the free-living stages ofSchistosoma mansoni . Z. Parasitenkd. 56, 99–106 (1978).

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  • Praziquantel
  • Copper Sulphate
  • Swimming Ability
  • Free Swimming
  • Tail Immersion