Effects of niclosamide on Oncomelania hupensis, the intermediate snail host of Schistosoma japonicum: an enzyme-histochemical study

An enzyme-histochemical study of five enzymes, namely succinate dehydrogenase (SDH), lactate dehydrogenase (LDH), cytochrome oxidase (CCO), cholinesterase (CHE) and nitric oxide synthase (NOS), was elucidated in the soft tissues of Oncomelania hupensis, the intermediate host snail of Schistosoma japonicum, before and after the treatment with a suspension concentrate of niclosamide (SCN). Following the treatment of SCN, a marked loss occurred in the activity of the five enzymes mentioned above. LDH and SDH showed their strongest activity in the buccal mass and muscular fibers, CCO in buccal mass and liver, CHE in pellicle and ganglia, and NOS in muscular fibers and pharyngeal canal. The results indicate that SCN impairs the activities of the enzymes influencing the transfer of neurotransmitter and energy supply in O. hupensis, ultimately leading to the loss of various physiological functions, which is considered to be a cause of death in O. hupensis.