| Schistosomiasis is a zoonotic parasitosis which is widely endemic in China. As the only intermediate host of Schistosoma japonicum, Oncomelania hupensis played a key role in transmission of schistosomiasis. The control of Oncomelania hupensis has always been the core content of integrated control strategy of schistosomiasis in our country. Of them, because of their high efficiency and simple operation, chemical molluscicides were the major method and played an important role in control of snail’s density. Preparation of niclosamide,50% wettable powder of niclosamide ethanolamine salt (WPN), which was the only chemical molluscicide for field use commended by WHO, is the most frequently used at present, but its molluscicidal mechanism is still entirely unclear. Recently, a derivative of niclosamide, the salt of quinoid-2’,5-dichloro-4’-nitro-salicylanilide (Liu Dai Shui Yang An, LDS), has been proved to have equivalent molluscicidal effect in lab and field as WPN, but with lower cost and significantly lower toxicity to fish than WPN. By morphological, enzymological and transcriptional level comparing of snail which were treated with above two molluscicide and water, molluscicidal mechanism of LDS and its similarities and differences compared to which of WPN were explored in this study. After immersion by WPN/LDS/H2O 3,6,12,24 h respectively, on the basis of determining the molluscicidal efficiency, morphologic changes of snails were observed by optic microscope observation after H & E and transmission electron microscope (TEM) observation. The results showed, treatment of WPN or LDS caused disorder of myofilaments of muscle cells and damage of some organelles such as nuclear, mitochondria, rough endoplasmic reticulums (rERs), and et al., and more serious damage of nuclear in muscle cells, more serious vacuolazation and fracture of ERs in liver were observed in LDS-treated snails. These changes suggested movement ability, liver function and energy metabolism were inhibited after molluscicidal treated. By enzyme histochemical staining and enzyme activity assay in soft body homogenate, the activities alteration after WPN/LDS treatment of 13 enzymes such as lactate dehydrogenase (LDH) were assayed. After molluscicidal treatment, activities of enzymes related with carbohydrate metabolism were inhibited except LDH increasedin muscle tissue, and activities of enzymes related with stress response increased followed by decreasing to lower levels than those of the H2O-treated group. This shift of carbohydrate metabolism patterns led to insufficient energy supply and lactic acid accumulation, and variations of enzymes related with stress response suggested a stress response of snail to the molluscicides at early stages and later fatal damage in liver and nervous system. In general, effects of WPN and LDS were similar although LDS-treated snails showed more serious damage in the liver and a stronger inhibition of enzymes related with aerobic respiration and stress response. On the basis of the above studies,254 unigenes differentially expressed after WPN/LDS treatment were screened by transcriptome sequencing. These genes were shown to be involved in cell structure defects and the inhibition of neurohumoral transmission and energy metabolism, which was consistent with the alteration of enzyme activities. However, considering enzyme activities at post-transcriptional and protein levels, comprehensive identification and annotation of potential enzyme-related genes and regulation pattern would be necessary to explored potential mechanism of these molluscicides. This transcriptome dataset will provide an opportunity for the in-depth analysis of O. hupensis at the molecular level and accelerate studies of the O. hupensis genome, and the data related the molluscicidal mechanism will be of great benefit in future snail control efforts. |
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