Abstract: Objective To investigate the effect of Eucalyptus robusta leaves extract against Echinococcus granulosus protoscolices in vitro. Methods Mature leaves of Eucalyptus robusta were collected on 24th day in each month from January to December 2012, and air-dried in the room. Ultrasonic extraction of the leaves was done with 4 solvents with different polarity, petroleum ether, dichloromethane, ethyl acetate and anhydrous ethanol. Protoscolices were incubated with the extract at various concentrations for 72 h, and mortality and median lethal dose（LC50） was calculated. Results The extracts were different in characteristics and yield. The petroleum ether extract was in the form of black oil, while dichloromethane, ethyl acetate and anhydrous ethanol extracts were in the form of dark green, pink and white powder respectively. The average yields by petroleum ether, dichloromethane, ethyl acetate, and anhydrous ethanol were 4.4%, 2.1%, 2.3% and 2.3%, respectively. The extract yield was highest for petroleum ether, with a yield of 5.4% in May. The mortality of protoscoleces in all monthly groups of petroleum ether and dichloromethane extracts reached 100% with the concentration of 100 μg/ml and the same mortality reached in most groups of petroleum ether extracts with the concentration of 50 μg/ml. The effects of dichloromethane extracts were less than petroleum ether extracts, but significantly stronger than those of ethyl acetate and ehanol extracts. Further studies conducted on petroleum ether and dichloromethane extracts showed, the lethal effect of petroleum ether extract ranked in month of preparation from strong to weak as June>March>November>April>February>May>October>August>December>July>January>September. In June, the LC50 was 2.577 μg/ml and 95% confidence interval was 0.85-6.22 μg/ml. The lethal effect of dichlorom ethane extract ranked in month of preparation from strong to weak as November>May>October>April>July>December>June>September>August>February>March>January. In November, the LC50 was 21.85 μg/ml, and 95% confidence interval was 12.38-36.28 μg/ml. Conclusion The Eucalyptus robusta leaves contain potential compounds against Echinococcus granulosus. Further experiments of isolation, analysis and identification are needed.

Key words: Eucalyptus robusta, Echinococcus granulosus, Protoscolices, Median lethal dose