Morphological and enzymatical observations in Oncomelania hupensis after molluscicide treatment: implication for future molluscicide development

Abstract

A preparation of niclosamide named 50 % wettable powder of niclosamide ethanolamine salt (WPN), the only chemical molluscicide available in China, has been widely used for Oncomelania hupensis control over the past 20 years, but its molluscicidal mechanism has not been elucidated yet. Recently, a derivative of niclosamide, the salt of quinoid-2',5-dichloro-4'-nitro-salicylanilide (Liu Dai Shui Yang An, LDS), has been proven to have equivalent molluscicidal effects as WPN but with lower cost and significantly lower toxicity to fish than WPN. In our previous study, gene expression profiling of O. hupensis showed significantly effects after these two molluscicides had been applied. This study was designed to use morphological and enzymological analyses to further elucidate the mechanism by which these molluscicides cause snail death. After WPN or LDS treatment, the number of mitochondria of O. hupensis was reduced and their cristae appeared unclear, heterochromatin gathered to be polarized, ribosome numbers of the rough endoplasmic reticulums (rERs) decreased, myofilaments in muscle cells became disordered and loose, and cytoplasm in some liver cells was concentrated. Damage of cell structures and organelles suggested inhibited movement ability and effects on liver and energy metabolism following treatment. In parallel, activities of enzymes related with carbohydrate metabolism were inhibited except lactate dehydrogenase (LDH) increased in muscle tissue, and activities of enzymes related with stress response increased followed by decreasing to lower levels than those of the HO-treated group. This shift of carbohydrate metabolism patterns led to insufficient energy supply and lactic acid accumulation, and variations of nitric oxide synthase (NOS), alanine aminotransferase (ALT), and superoxide dismutase (SOD) during process of molluscicide treatment 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. This was consistent with the transcriptome profile obtained previously. 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 provide great benefit for understanding of potential mechanism of these molluscicides and even for future molluscicide development.

Spatiotemporal pattern analysis of schistosomiasis based on village level in the transmission control stage in lake and marshland areas in China

“…Most marshlands were soaked in water in summer and covered with grass as floodwaters recede in winter. Such geographical environmental conditions are conducive for O. hupensis snail growth and reproduction (Xiong et al ., 2016; Zhu et al ., 2017; Zhao et al ., 2018). The snail areas in these counties were larger than those in other regions.…”

A Survey and Ecological Risk Assessment of Niclosamide and Its Degradation Intermediate in Wucheng Waters within Poyang Lake Basin, China

“…Niclosamide, 5-chloro-N-(2-chloro-4-nitrophenyl)-2-hydroxybenzamide is the most important component of control programs for the freshwater snails that serve as intermediate hosts for the trematodes causing schistosomiasis [1][2][3] and fascioliasis in humans and domestic animals in many tropical and subtropical countries [4]. In China's schistosomiasi control area, NCL is used to kill snails and schistosomiasis, repel human and animal mites, and the annual usage exceeds 3,200 tons [5] After being used in the application site, NCL does not use any effective technical means for treatment, and discharged arbitrarily, which has a serious impact on the regional ecological environment [6].…”

Apropos: critical analysis of molluscicide application in schistosomiasis control programs in Brazil

“…In addition, WPN treatment resulted in damages to cell structures and organelles of O. hupensis snails, suggesting the suppression of the movement ability and effects on liver and energy metabolism; in parallel, activities of carbohydrate metabolism-associated enzymes were inhibited, and activities of stress response-associated enzymes were increased followed by a reduction to lower levels than those of the H 2 O-treated group [18]. This shift of carbohydrate metabolism patterns led to insufficient energy supply and lactic acid accumulation [18].…”

“…In addition, WPN treatment resulted in damages to cell structures and organelles of O. hupensis snails, suggesting the suppression of the movement ability and effects on liver and energy metabolism; in parallel, activities of carbohydrate metabolism-associated enzymes were inhibited, and activities of stress response-associated enzymes were increased followed by a reduction to lower levels than those of the H 2 O-treated group [18]. This shift of carbohydrate metabolism patterns led to insufficient energy supply and lactic acid accumulation [18]. Variations of nitric oxide synthase (NOS), alanine aminotransferase (ALT), and superoxide dismutase (SOD) during the WPN treatment suggested a stress response of O. hupensis snail to the molluscicide at early stages and later fatal damage in the liver and the nervous system [18].…”

“…This shift of carbohydrate metabolism patterns led to insufficient energy supply and lactic acid accumulation [18]. Variations of nitric oxide synthase (NOS), alanine aminotransferase (ALT), and superoxide dismutase (SOD) during the WPN treatment suggested a stress response of O. hupensis snail to the molluscicide at early stages and later fatal damage in the liver and the nervous system [18]. However, the environmental issues related to the use of WPN have not been clearly demonstrated to date.…”