| Schistosoma japonicum is a serious epidemic disease in China. Oncomelania hupensis is the unique snail intermediate host of Schistosomasis japonicum., which play a very important role for the transmission of schistosomiasis. Using molluscicide to control the snails is one of the most effectively and important measures. In order to change the present situation of using unique molluscicide named niclosamide (WPN), which was recommend by the World Health Organization (WHO). A new molluscicide called Quinoid niclosamide (LDS,the salt of quinoid-2',5-dichloro-4'-nitrosalicylanilide, derived from niclosamide) has been discovered and developed. In this research. Four preparations of LDS were provided through screen the effective preparation for killing snails, the most effective preparation was selected and tested in the lab and the field to further identified the molluscicidal effect. At the same time, the most effective preparation of LDS was also to do other researches on the mechanism for the killing snails, the acute toxicity to the animals, and the cost analysis and evaluation1. Screening best preparations from LDS10% LDS was composed of 10% pure molluscicide of Salt of quinoid-2',5-dichloro-4'-nitrosalicylanilide and 90% different proportions of dispersant, suspending agent, stabilizer and stuffing bulking agent (active diatomite),which composed by different production process (i.e., reaction time, reaction temperature and reaction media, etc.). The different proportion of filling agent and production process (total called preparation), could be directly influenced the cost and the effect of the LDS. In this chapter, the best preparations would be selected from the four different preparations of LDS (B1, B2, B3, B4) by immersion and spraying method in laboratory.The results showed that, killing snails by immersion, the mortality of snail was increased following exposure time getting longer and concentration increasing(p<0.05).At 48h or 72h, all the snails were dead at concentrations above 0.4mg/L. Snail mortality of B2 preparation reaches 100% firstly. LC50 for 72h exposure was less than 1mg/L. and B2 was the minimum. Killing snails by spraying at dosage of 0.2 g/m2, after exposure 72h, snail mortality of B1 and B2 preparation were both 95%, B3 and B4 were both below 95%; at dosage of 0.4g/m2, the snail mortality of B, and B2were 100% and 95%, B3 and B4 was 92% and 88% respectively. Statistical results show that B1 and B2 have no statistical significant differences with WPN (p>0.05), and spraying effectiveness was better than B3 and B4 (p<0.05); LC50 were less than 1 g/m2. and B2 preparation was the minimum.According to the natioal method of agriculture standard of Pharmacodynamics and evaluation for molluscicide registration" (NY/T 1617 2008), as well as the comprehensive consideration of the experimental results, B2 preparation was be chosen for the quantity production, which would make a foundation for the repeated test in the laboratory and the field.2. Evaluation of LDS in the control of Oncomelania hupensis in LabQuantity production of B2 preparation of LDS were used to test repeatedly in Lab.The results showed that the mortality of the snail increased fowlling exposure time getting longer and concentration increasing.Killing snails by immersion, all the snails were dead at concentration of 0.2mg/L after exposure for 72h, or at concentration of 0.4mg/L to exposure for 48h or longer. Killing snails by spraying, at dosage 0.2g/m2 or above the dosages after for 72h or above, the mortality were all above 95% at each time interval. Killing snails by powdering, at dosage 0.8g/m2 or above the dosages, after 168h or above, the mortality were all over 95% at each time interval. Killing snail eggs by immersion, the snails egg were dead at concentrations 0.4mg/L or above the dosages. There mortality was above 90% at each time interval. The results showed that there was no statistically significant difference between LDS and WPN in their molluscicidal effects (P>0.05). but LDS was got the effect more quickly than WPN (p<0.05)According to the natioal method of agriculture standard of" Pharmacodynamics method and evaluation for molluscicide registration" (NY/T 1617 2008), killing snail at concentrations of 0.2mg/L by immersion, or 0.2g/m2 by spraying, LDS can reach the standard. These preliminary results indicate that LDS was a new molluscicide that can be used in the field. Considering the complex snail breeding environment in the field, the dosage of LDS can be appropriately increased suitably.3. Evaluation of LDS in the control of Oncomelania hupensis in the fieldThe molluscicidal effect of LDS was evaluated and compared with WPN by immersion, spraying and powdering method in marshland and flood plain of the Yangtze River of Wuhan and Xiaogan city, Hubei province, and other provinces in China.The results in Wuhan city showed that, at 72h, all the snails were dead and at concentrations 0.2mg/L; at 48h or above, all the snails were dead at concentrations 0.4mg/L or above. The differences between LDS and WPN have no statistically significant differences at 72h(p>0.05), but have statistically significant differences at 48h (p<0.05),the mortality of LDS were considerably higher than WPN during the time interval. The mortality of the snail by spraying and powdering were the same. The molluscicidal efficacy of LDS was the same with WPN, but LDS was got the effect more rapidly than WPN.Application study were taken in these areas as followed, mountain type hills subtype (Jinshan county, Zhongxiang county), lakes and marshes type bottomland subtypes (Xiaonan district, Yincheng city, Honghu city), lakes and marshes type lake branch subtypes (Yangxin county), lakes and marshes type channel subtype (Qianjiang city, Gongan county, Jiayu county, Jianli county). The results showed that, the molluscicidal efficacy of the LDS and WPN were the same (p>0.05). At concentration of 0.2 mg/L, and 72h exposure by immersion, snail mortality were all over 95%; at dosage of 0.4g/m2, and 168h exposure by spraying, snail mortality were all over 85%; at dosage of 0.6g/m2. and 168h exposure by powdering, snail mortality were all over 85%. The results showed that the differences between LDS and WPN have no statistically significant difference by immersion (p>0.05). The molluscicidal efficacy of Lakes and marshes type channel subtype was lower than other types by spraing and powdering.The large-scale tests for molluscicidal effect were taken in Anhui, Hunan, Jiangsu, Sichuan and Yunnan provinces. The results showed that, at concentration of 0.2 mg/L, and 72h exposures by immersion, the snail mortality were all over 96% except Anhui province. Hunan group can reach 100%. At dosage of 0.4g/m2, and 72h exposure by spraying, the most of snail mortality were over 85%. Hunan group has a statistically significant difference to other provinces (p<0.05); at the dosage of 0.6g/m2 and 168h exposure by spraying, the snail mortality were all over 86%. At the dosage of 0.6g/m2, and 72h exposure by powdering, the snail mortality were all over 85%. The results of tests showed that the it have no statistically significant differences between LDS and WPN (p>0.05).The molluscicidal efficacy of the LDS was same to WPN. According to statistics, the molluscicidal efficacy were difference among the geographical type provinces. The results showed that snail mortality are different in Lakes and marshes type provinces by spraying (p<0.05).there were no statistically significant differences by other method (p>0.05). So the molluscicidal efficacy of the LDS was stable in the same geographic type. The mountain type have better molluscicidal efficacy than lakes and marshes type. Spraying or powdering method was more suitable in lakes and marshes type.Use molluscicide LDS by immersion at concentration of 0.4mg/L and spraying at concentration of 0.6g/m2 as a recommend dose for the control of Oncomelania hupensis in the field.4. Acute toxicity test of LDS in the labBased on "Chemical pesticide environmental safety test evaluation standard"and"The method of toxicity test for agriculture register" (GB 15670-1995), acute toxicity test was carried out by the quail, bee, silkworm, zebrafish, and also via mouth, skin and inbreathe by Wistar rat. Meanwhile the test of eye and skin stimulate by rabbit as well as test of skin stimulate by guinea pig were also conducted.Based on the classification of appraising standard on acute toxicity test. LDS has no toxicity to guinea pig, low toxicity to bee and silkworm, medium toxicity to zebrafish, feebleness toxicity to Wistar rat, and no acute eye and skin stimulate to the rabbit, but feebleness impressible to guinea pig. Compared with WPN, LDS reduced toxicity via mouth to Wistar rat. It would be more safety to the mammals.Meanwhile, the toxicity to the fish was lower than WPN, which was more suitable for the field application.5. Observation of ultra structure on LDSThe enzymes'histochemical studies shows after immersing in LDS solution,the snail dead for the changes in the liver In this chapter, the changes of liver cell ultrastructure were examined by Transmission Electron Microscope.The results of tests showed that, after immersing in LDS solution, the liver cell was swollen and degenerated, heterochromatin increase. Some of the cell nucleuses were atrophied, coagulated or dissolved. The rough endoplasmic reticulum (RER) expanded, vacuolated concentric circles, and some of the mitochondrial ridges were swollen, destroyed, and disappeared. The secretory granules in the cell increased. the change of liver cell ultrastructure of WPN were similar to LDS.LDS destroyed the structure of the mitochondria and endoplasmic reticulum, which may suppress the release and utilization of ATP in the Oncomelania snails and finally causes death of snails. LDS damage the structure of liver cell, was one of the most important causes for the death of snails.6. Evaluation of cost effectiveness of LDSIn this chapter, cost effectiveness of LDS, WPN and RongBao would be systematic compared and evaluate by drug costs, human resource cost, unit killing snail cost and unit cost killing snail area.As killing the snails by immersion method over the same area of one hectare, using LDS needs 600 Chinese RMB (Yuan), while using RongBao needs 1200 Chinese RMB (Yuan)and WPN needs 730 Chinese RMB (Yuan). It is clear that the cost of LDS is 50% lower than the cost of RongBao and 18% lower than the cost of WPN.Unit killing snail cost results showed, cost price of LDS was 0.066 Yuan/m2,WPN was 0.079 Yuan/m2,RongBao was 0.129 Yuan/m2。In the same charges of 10000 yuan, killing snail area LDS was 15.152 hm2,WPN was12.658hm2,RongBao was 7.752 hm2, the area of LDS increase 20% of WPN and 95% of RongBao.To sum up. from the social benefit and economic benefit analysis, LDS has many advantages, such as short work time, good efficiency, strong stability, low toxicity and non-toxic to aquatic animals and mammals, low cost ect. LDS can be applied to application use to control the snail, in order to change the present situation of the single molluscicide. It can also make a contribution in the schistosomiasis control in our country.
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