In current study, a few sheep cystic livers and lungs were obtained from Mashhad slaughter house and protoscolex were separated aseptically. Thirty 6-week-old Swiss mice were divided into 5 groups and two thousands of live protoscolices were inoculated intrapritoaneally in each mouse. In group 1 and 2 (prophylactic groups), mice were given 150 mg/kg of oral albendazole and mebendazole for 10 days. In group 3 and 4 (treated groups), mice were treated orally with 300 mg/kg of albendazole and mebendazole for 22 days with an interval of 2 days after every 4 days of treatment 6 months after inoculation. The control group (group 5), was sham injected with normal saline. Mice were killed after 7 months and internal organs were observed for hydatid cyst. In group 1, 2 cysts were observed in the liver of mice. In this group, although albendazole did not prevent cyst formation, but the number and also the size of the cysts were lower and smaller than the control group. In group 2, 3 cysts were observed in internal organs. In group 3, there was no cyst in internal organs and so in this group it is concluded that albendazole prevented cyst formation. In group 4, 1 cyst was observed on the liver of mice. In control group a lot of cysts were observed in internal organs of mice and the average size of cysts were bigger than prophylactic and also treatment groups.

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