A comparison of the effect of albendazole, cambendazole, and thiabendazole on the larval development of three hymenolepidid cestodes.

Flour beetles (Tribolium confusum) parasitized either by Hymenolepis diminuta, H. nana, or H. microstoma were fed continuously on flour mixed either with thiabendazole, cambendazole, or albendazole (drug concentration was always 10%) from day 1 (24 hr) to day 10 postinfection when the experiments were terminated. All drugs markedly inhibited the development of H. diminuta and H. nana. Populations of these species recovered from beetles fed anthelmintics were composed mostly of under-developed forms, many of which still retained the size and appearance of newly hatched oncospheres, whereas all the parasites recovered from the control beetles (fed only flour) reached full development. Parasites inhibited by cambendazole and albendazole recovered and reached full development within 9 days after treatment was terminated. Also, results were obtained which implied that some parasites were able to continue their development at a reduced rate in the presence of the drugs. Hymenolepis microstoma differed from the other species in its response to the drugs. Albendazole and thiabendazole had no effect on its development and it was only slightly inhibited by cambendazole. Larvae recovered from beetles fed the latter drug had all developed beyond the oncosphere stage but 3 to 5% of them repeatedly failed to reach full development. The drugs varied in their effects on the flour beetles. An average of 63% and 33% of those fed thiabendazole and cambendazole, respectively, died before the 10th day of infection. Albendazole, on the other hand, had no effect on beetle survival.