The lethal effect of mebendazole on secondaryEchinococcus granulosus, cysticerci ofTaenia pisiformisand tetrathyridia ofMesocestoides corti

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Abstract
Oral administration of mebendazole at a rate of 1 g/kg ieed (approximately 50 mg/kg body weight/day) for 14 days killed mature and immature cysticerci ofTaenia pisiformisin rabbits, and multiplying tetrathyridia ofMesocestoides cortiin mice. Progressive degrees of parasite damage caused by mebendazole treatment could be assessed by histological examination of calcareous corpuscles. A single subcutaneous injection of 10% mebendazole in carrier, at a rate of 100 mg/kg body weight, resulted in the death of allM. cortitetrathyridia in mice within 4 weeks, but the drug in saline was slowly mobilized and was relatively ineffective. Neither subcutaneous injections of mebendazole in saline or in carrier could kill cysticerci ofT. pisiformiswithin 5 weeks, but the drug in carrier was effective after several months. Mebendazole in saline was effective when injected intraperitoneally, but adhesions often resulted from this route of administration.Echinococcus granulosusprotoscoleces administered to mice by intraperitoneal injection were rapidly encapsulated by host lymphoid cells. The vesiculating protoscoleces were all contained within a fibrous capsule for more than 2 months after infection, but by 4 months almost all had grown free of the host reaction. Treatment of the encapsulated protoscoleces with mebendazole in feed for 14–21 days caused collapse of the outer cysts and death of the germinal membrane of all but the innermost protoscoleces. Six weeks later, however, cysts had regrown from surviving germinal tissue and a further treatment with mebendazole in feed for 14–21 days again did not destroy all germinal cells. Treatment of the 4-month-old scoleces with mebendazole in feed for 14 days caused all cysts to collapse and destroyed practically allE. granulosusgerminal tissue. Three subcutaneous injections of mebendazole at fortnightly intervals, of drug in saline at 500 mg/kg body weight, or in carrier at 100 mg/kg body weight, were required in order apparently to kill all secondary cysts ofE. granulosus. Host lymphoid cells were not able to traverse the laminated membrane of either untreated or collapsed cysts, and it has been shown that only a small amount of living germinative tissue is required to produce a newE. granulosus cyst. These factors could contribute to the relative ability ofE. granulosuscysts to recover from mebendazole treatment, compared with cysticerci or tetrathyridia. The effectiveness of mebendazole thus seemed to depend on the formulation of the drug and its route of administration. Mebendazole is probably the first anthelmintic to have a lethal effect on larval cestodes. When applied orally there do not appear to be any adverse effects due to treatment.

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