Evaluating the effect of a novel molluscicide in the endemic schistosomiasis japonica area of China

Oncomelania hupensis is the sole intermediate host snail of Schistosoma japonicum in China. Snail control by molluscicide remains one of the most effective measures of schistosomiasis japonica control. A 50% wettable powder of niclosamide ethanolamine salt (WPN) is widely used for snail control in China. However, WPN is costly and toxic to fish. A novel molluscicide named LDS, the salt of quinoid-2', 5-dichloro-4'-nitrosalicylanilide from niclosamide, has been developed. To evaluate the effects of large-scale field application of LDS on field snail control, tests were conducted in 15 counties of Hubei Province, China. Active adult snails, were immersed in 0.2, 0.4, and 0.6 g/m3 of 10% LDS, 1.0 g/m3 of 50% WPN was used as the molluscicide control, and then the mortality rates of snails were investigated after 1, 2, and 3 days. In addition, four active concentrations of 10% LDS (0.4, 0.6, 0.8 and 1.0 g/m2) were applied by spraying and powdering in the field. 1.0 g/m2 of 50% WPN was used as the molluscicide control, and then the mortality rates of snails were observed after 1, 3, and 7 days. The results indicated that 0.4 g/m3 LDS applied by the immersion or 0.6 g/m2 LDS applied by spraying and powdering achieved the same molluscicidal effect as that of WPN, regardless of exposure time. By using different methods, the snail mortality rates in the molluscicide groups were related to exposure time and concentration, respectively. LDS costs less than WPN; thus, LDS is suitable and applicable for use as a molluscicide in schistosomiasis japonica epidemic areas.

STAT3 modulation to enhance motor neuron differentiation in human neural stem cells

Spinal cord injury or amyotrophic lateral sclerosis damages spinal motor neurons and forms a glial scar, which prevents neural regeneration. Signal transducer and activator of transcription 3 (STAT3) plays a critical role in astrogliogenesis and scar formation, and thus a fine modulation of STAT3 signaling may help to control the excessive gliogenic environment and enhance neural repair. The objective of this study was to determine the effect of STAT3 inhibition on human neural stem cells (hNSCs). In vitro hNSCs primed with fibroblast growth factor 2 (FGF2) exhibited a lower level of phosphorylated STAT3 than cells primed by epidermal growth factor (EGF), which correlated with a higher number of motor neurons differentiated from FGF2-primed hNSCs. Treatment with STAT3 inhibitors, Stattic and Niclosamide, enhanced motor neuron differentiation only in FGF2-primed hNSCs, as shown by increased homeobox gene Hb9 mRNA levels as well as HB9+ and microtubule-associated protein 2 (MAP2)+ co-labeled cells. The increased motor neuron differentiation was accompanied by a decrease in the number of glial fibrillary acidic protein (GFAP)-positive astrocytes. Interestingly, Stattic and Niclosamide did not affect the level of STAT3 phosphorylation; rather, they perturbed the nuclear translocation of phosphorylated STAT3. In summary, we demonstrate that FGF2 is required for motor neuron differentiation from hNSCs and that inhibition of STAT3 further increases motor neuron differentiation at the expense of astrogliogenesis. Our study thus suggests a potential benefit of targeting the STAT3 pathway for neurotrauma or neurodegenerative diseases.

Niclosamide inhibits androgen receptor variants expression and overcomes enzalutamide resistance in castration-resistant prostate cancer

PURPOSE

Enzalutamide, a second-generation antiandrogen, was recently approved for the treatment of castration-resistant prostate cancer (CRPC) in patients who no longer respond to docetaxel. Despite these advances that provide temporary respite, resistance to enzalutamide occurs frequently. Androgen receptor (AR) splice variants such as AR-V7 have recently been shown to drive castration-resistant growth and resistance to enzalutamide. This study was designed to identify inhibitors of AR variants and test its ability to overcome resistance to enzalutamide.

EXPERIMENTAL DESIGN

The drug screening was conducted using luciferase activity assay to determine the activity of AR-V7 after treatment with the compounds in the Prestwick Chemical Library, which contains about 1,120 FDA-approved drugs. The effects of the identified inhibitors on AR-V7 activity and enzalutamide sensitivity were characterized in CRPC and enzalutamide-resistant prostate cancer cells in vitro and in vivo.

RESULTS

Niclosamide, an FDA-approved antihelminthic drug, was identified as a potent AR-V7 inhibitor in prostate cancer cells. Niclosamide significantly downregulated AR-V7 protein expression by protein degradation through a proteasome-dependent pathway. Niclosamide also inhibited AR-V7 transcription activity and reduced the recruitment of AR-V7 to the PSA promoter. Niclosamide inhibited prostate cancer cell growth in vitro and tumor growth in vivo. Furthermore, the combination of niclosamide and enzalutamide resulted in significant inhibition of enzalutamide-resistant tumor growth, suggesting that niclosamide enhances enzalutamide therapy and overcomes enzalutamide resistance in CRPC cells.

CONCLUSIONS

Niclosamide was identified as a novel inhibitor of AR variants. Our findings offer preclinical validation of niclosamide as a promising inhibitor of AR variants to treat, either alone or in combination with current antiandrogen therapies, patients with advanced prostate cancer, especially those resistant to enzalutamide.

[The vibrio-static test with niclosamide to identify bacteria of genus Vibrio]

The new vibrio-static niclosamide (CAS No 50-65-7) is revealed. The vibrio-static test with niclosamide (10 mkg/disc) to identify bacteria of genus Vibrio is developed. This test by its diagnostic sensitivity surpasses the vibrio-static test with vibrio-static O129 since it suppresses growth of vibrios having cross resistance to O129 and co-trimoxazole. The vibrio-static test with niclosamide made it possible to identify all examined strains of V. metschnikovii, V. vulnificus, V. parahaemolyticus, V. cholerae non O1/non O139.

[Effects of molluscicides at different environments on Oncomelania hupensis snail control in Danyang City]

OBJECTIVE

To evaluate the effects of continuous application of niclosamide ethanolamine salt on Oncomelania hupensis snail control in a marshland, river and channel.

METHODS

The Beiwei marshland in Houxiang Town, the Xiaoliang River in Lingkou Town and Laomiao channel in Yunyang Town in Danyang City were selected as study sites, and 4% niclosamide ethanolamine salt and 26% niclosamide powder were used to kill the snails. Based on the historical records and field investigations, the effects of continuous application of niclosamide ethanolamine salt on snail control were evaluated.

RESULTS

Compared with the first time of snail repetition, the snail areas decreased by 82.80%, 63.14% and 70.00% in the Beiwei marshland, Xiaoliang River and Laomiao channel, respectively, in 2013. There was a positive correlation between the area and density of snails (r = 0.931, 0.975 and 0.916, respectively; all P values < 0.05). The average densities of living snails decreased significantly by 92.34%, 87.91% and 97.66%, respectively. There was a negative correlation between the corrected mortality of snails and the average density of living snails in the following year, and a negative correlation between the reduction rate of living snail density and the average density of living snails in the following year.

CONCLUSION

Molluscicides plays an important role in compressing the snail area, reducing the snail density, and controlling the schistosomiasis transmission.

The anthelmintic drug niclosamide induces apoptosis, impairs metastasis and reduces immunosuppressive cells in breast cancer model

Breast carcinoma is the most common female cancer with considerable metastatic potential. Discovery of new therapeutic approaches for treatment of metastatic breast cancer is still needed. Here, we reported our finding with niclosamide, an FDA approved anthelmintic drug. The potency of niclosamide on breast cancer was assessed in vitro and in vivo. In this investigation, we found that niclosamide showed a dramatic growth inhibition against breast cancer cell lines and induced apoptosis of 4T1 cells in a dose-dependent manner. Further, Western blot analysis demonstrated the occurrence of its apoptosis was associated with activation of Cleaved caspases-3, down-regulation of Bcl-2, Mcl-1 and Survivin. Moreover, niclosamide blocked breast cancer cells migration and invasion, and the reduction of phosphorylated STAT3(Tyr705), phosphorylated FAK(Tyr925) and phosphorylated Src(Tyr416) were also observed. Furthermore, in our animal experiments, intraperitoneal administration of 20 mg/kg/d niclosamide suppressed 4T1 tumor growth without detectable toxicity. Histological and immunohistochemical analyses revealed a decrease in Ki67-positive cells, VEGF-positive cells and microvessel density (MVD) and an increase in Cleaved caspase-3-positive cells upon niclosamide. Notably, niclosamide reduced the number of myeloid-derived suppressor cells (MDSCs) in tumor tissues and blocked formation of pulmonary metastases. Taken together, these results demonstrated that niclosamide may be a promising candidate for breast cancer.

[Field evaluation of a novel plant molluscicide "Luo-wei" against Oncomelania hupensis IV molluscicidal effect in field of river beach in Dongzhi County, Anhui Province]

OBJECTIVE

To evaluate the field effect of the plant molluscicide "Luo-wei" (tea-seed distilled saponins, TDS) against the snail Oncomelania hupensis in the river beach in Anhui Province.

METHODS

The immersing and spraying experiments were carried out in the river beach in Dongzhi County, Anhui Province, to assess the molluscicidal effect of 4% TDS comparing with 50% wettable powder of niclosamide ethanolamine salt (WPN). The chi(2) test or Fish's exact test was used to examine the differences between or among the molluscicidal effects by different environments, molluscicides, application methods, or days after the intervention. Meanwhile, the cost-effectiveness of the two molluscicides was analyzed.

RESULTS

After 1, 2 , 3 d and 7 d of the immersion, the snail death rates in both TDS group and WPN group increased gradually, the snail death rates in the two groups after immersing for 7 d were 94.62% and 99.24%, respectively, and there was no significant difference between them ( chi(2) = 3.30, P > 0.05). After 1 , 3 , 7 d and 15 d of spraying, the snail death rates were 70.82%, 79.75%, 85.11% and 91.65% in the TDS group, and 77.71%, 84.27%, 91.90% and 95.58% in the WPN group, respectively, and the differences among the snail death rates of the two groups at each time point were statistically significant (all P values < 0.05). The costs of spraying were 316.71 yuan per 100 m2 for TDS and 309.71 for WPN.

CONCLUSIONS

The molluscicidal effect of TDS has reached the requirements of national standard on nature source pesticides in the river beach of the middle and lower reaches of the Yangtze River. It is necessary to further evaluate its cost-effectiveness in large-scale field experiments in the future.

[Effect of a novel plant molluscicide "Luo-wei" against Oncomelania hupensis in plateau mountain areas]

OBJECTIVE

To evaluate the effect of a novel plant molluscicide, 4%"Luo-wei" (Tea-seed distilled saponins, TDS) against Oncomelania hupensis snails in plateau mountain areas in Yunnan Province.

METHODS

The immersing and spraying experiments were carried out in the ditches and grassland of Xiaolian Administrative Village in Heqing County, Yunnan Province, to assess the molluscicidal effect of 4% TDS comparing with 50% wettable powder of niclosamide ethanolamine salt (WPN) in different environments and time.

RESULTS

After immersion for 24, 48 h and 72 h, the snail death rates were 70.67%, 87.33% and 98.67% in the TDS group, whereas being 77.33%, 96.67% and 100.00% in the WPN group, respectively. The differences of the death rates between the two groups 24 h and 72 h after immersing were not statistically significant ( chi2(24h) =1.73, chi2(72h) = 2.01, both P values > 0.05). Seven days after the immersing experiments, the occurrence rate of frames with living snails and the death rate of snails were 20.00% and 93.03% in the TDS group, while those were 13.33% and 95.76% in the WPN group, and there were no significant differences of the 2 indexes between the 2 groups ( chi(2)(Occurrence rate) = 2.27, chi(2)(Death rate) = 0.94, all P values > 0.05). After spraying for 1, 3, 7 d and 15 d, in both groups, the occurrence rates of frames with living snails and the average densities of living snails gradually declined, while the death rates of snails gradually increased with the extension of time. There were no statistically significant differences of the above 3 indexes between the 2 groups (all P values > 0.05). Fifteen days after the spraying experiment, the occurrence rate of frames with living snails and the adjusted death rate of snails were 15.00% and 87.39% in the TDS group and those were 16.67% and 89.32% in the WPN group, respectively.

CONCLUSION

The molluscicidal effect of TDS is satisfying in plateau mountain areas, and the molluscicide is worthy of further extension and application.

Identification of three antiviral inhibitors against Japanese encephalitis virus from library of pharmacologically active compounds 1280

Japanese encephalitis virus (JEV) can cause severe central nervous disease with a high mortality rate. There is no antiviral drug available for JEV-specific treatment. In this study, a cytopathic-effect-based, high-throughput screening assay was developed and applied to screen JEV inhibitors from Library of Pharmacologically Active Compounds 1280. The antiviral effects of three hit compounds including FGIN-1-27, cilnidipine, and niclosamide were evaluated in cells by western blotting, indirect immunofluorescence assay, and plaque reduction assay. A time-of-addition assay proved that all three compounds inhibited JEV at the stage of replication. The EC50s of FGIN-1-27, cilnidipine, and niclosamide were 3.21, 6.52, and 5.80 µM, respectively, while the selectivity indexes were 38.79, 30.67, and 7.49. FGIN-1-27 and cilnidipine have high efficiency and selectivity against JEV. This study provided two JEV antiviral inhibitors as candidates for treatment of JEV infection.

[Molluscicidal effects of nano-silver biological molluscicide and niclosamide]

OBJECTIVE

To evaluate the molluscicidal effect of a novel nano-silver biological molluscicide in the field and its toxicity to other aquatic organisms.

METHODS

A marshland of the Qiupu River was selected as the study site. Four 1 m3 pools were excavated. Four groups, including 300 g/m3 and 600 g/m3 nano-silver biological molluscicide groups, a 2 g/m3 50% niclosamide group, and a natural water (control) group were assigned to the four pools which had 100 Oncomelania hupensis snails and 100 crucian seedlings. The molluscicidal effects and toxicity to the aquatic organisms were observed.

RESULTS

The snail death rates were 100% and crucian seedling death rates were 6% in the 600 g/m3 nano-silver biological molluscicide group and 300 g/m3 nano-silver biological molluscicide group in 7 days and 14 days. The snail death rate was 100% in the niclosamide group in 7 days, and the crucian seedling death rate was 100% in the niclosamide group in 3 days. The snail death rates were 7% and 14% in the control group in 7 and 14 days respectively, and the crucian seedling death rate was 22% in the control group.

CONCLUSIONS

The novel nano-silver biological molluscicide possesses an excellent molluscicidal capability and non-toxicity to the other aquatic organisms. Therefore, it may become a new, efficient and environment-friendly bio-molluscicide for extensive application.

[Preparation and molluscicidal effect of 5% niclosamide ethanolamine granules]

OBJECTIVE

To explore the preparation of 5% niclosamide ethanolamine granules and evaluate its molluscicidal effect.

METHODS

The optimal formula was obtained by the selection of wetting agents, dispersants, adhesives and carriers. The molluscicidal effect of 5% niclosamide ethanolamine granules was measured by the spray methods in the laboratory and field.

RESULTS

The mixed 5% niclosamide ethanolamine, 0.2% sodium lauryl sulfate, and 1% alkylphenol sulfonic polyxyethylene ether sulfonate were crushed by gas flow, and then mixed with 93.7% quartz sand and 0.1% polyvinyl alcohol water solution, drying to 5% niclosamide ethanolamine granules. The density, bulk density, and moisture of 5% niclosamide ethanolamine granules were 1.4 g/ml, 1.3 g/ml, and 2.4%, respectively, and the hot storage stability was qualified. Under the lab condition, the death rates of Oncomelania hupensis snails sprayed with 0.5 g/m2 (7 d) or 1.0 g/m2 (1 d) of 5% niclosamide ethanolamine granules were higher than 95%. In the field, the death rates of the snails sprayed with 0.5 g/m2 (7 d) or 1.0 g/m2 (1 d) were higher than 85%.

CONCLUSION

There is a high molluscicidal effect of 5% niclosamide ethanolamine granules and it is suitable for field application.

[Field evaluation of a novel plant molluscicide "Luo-wei" against the snail Oncomelania hupensis III molluscicidal effect by spraying method in hilly regions]

OBJECTIVE

To evaluate the molluscicidal effect of a novel plant molluscicide "Luo-wei" (Tea-seed distilled saponins, TDS) against Oncomelania httpensis in billy regions.

METHODS

The molluscicidal effect of TDS at a dose of 5 g/m2 by the spraying method against Oncomelania snails was assessed in a setting with a high snail density in Husban Village, Jiangning District of Nanjing City, and the effect was compared with that of 50% wettable powder of niclosamide ethanolamine salt (WPN) at a dose of 2 gIm2 at different time after spraying.

RESULTS

Afterl, 3, 7 and 15 day (days) of the spraying experiment, the snail death rates of the TDS group were 56.47%, 57.32%, 90.58% and 93.41% respectively, while those of the WPN group were 49.22%, 53.37%, 95.92% and 97.26%, respectively. The differences between the rates of the 2 groups 1, 7, 15 day (days) after the spraying were statistically significant (all P < 0.05). Fifteen days after the spraying, the density of living snails reduced from 20.30 +/- 16.20 snails/0.1 m2 and 23.67 +/- 21.22 snails/0.1 m2 to 2.28 +/- 2.17 snails/0.1 m2 and 1.27 +/- 0.76 snailsl0.1 m2 in the TDS group and WPN group, respectively, with the reduction rates of 88.77% and 94.63%, respectively.

CONCLUSION

TDS can be used as an alternative molluscicide for the control of Oncornelania snails in hilly areas, which deserves further popularization.

[Field evaluation of a novel plant molluscicide "Luo-wei" against Oncomelania hupensis snails II molluscicidal effect in the field of lake areas in Hanchuan City, Hubei Province]

OBJECTIVE

To evaluate the effect of a novel plant molluscicide "Luo-wei" (Tea-seed distilled saponins, TDS) against Oncomelania hupensis in the field of lake areas in Hanchuan City, Hubei Province.

METHODS

Immersing experiment and spraying experiment were carried out in 5 ditches and a beach land respectively in Hanchuan City, Hubei Province to compare the molluscicidal effects among 4% TDS, 50% wettable powder of niclosamide ethanolamine salt (WPN), and 26% suspension concentrate of metaldehyde and niclosamide (MNSC) by different dosages and time. The chi2 test or Fish's exact test was used to examine the differences of snail death rates among them.

RESULTS

After 72 h of immersing experiment, the snail death rates in the 2.5 g/m3 TDS group, 3.0 g/m3 TDS group, 2.0 g/m3 WPN group and 2.0 g/m3 MNSC group were 99.33%, 100%, 100%, and 100%, respectively, and there was no significant difference among them (P > 0.05). By the end of 15 d after the spraying experiments, the snail death rates were 91.86% in the 2.0 g/m2 MNSC group, 90.26% in the 5.0 g/m2 TDS group, 87.45% in the 2 g/m2 WPN group, and 86.10% in the 3 g/m2 TDS group. The differences between the 5.0 g/m2 TDS group and 2.0 g/m2 MNSC group, as well as the 3.0 g/m2 TDS group and the 2.0 g/m2 WPN group had no statistical significance (both P > 0.05).

CONCLUSIONS

The molluscicidal effect of TDS is similar to that of WPN or MNSC. The recommended dosage of TDS is 2.5 g/m3 for immersing or 5 g/ m2 for spraying in the field.

Drug screening identifies niclosamide as an inhibitor of breast cancer stem-like cells

The primary cause of death from breast cancer is the progressive growth of tumors and resistance to conventional therapies. It is currently believed that recurrent cancer is repopulated according to a recently proposed cancer stem cell hypothesis. New therapeutic strategies that specifically target cancer stem-like cells may represent a new avenue of cancer therapy. We aimed to discover novel compounds that target breast cancer stem-like cells. We used a dye-exclusion method to isolate side population (SP) cancer cells and, subsequently, subjected these SP cells to a sphere formation assay to generate SP spheres (SPS) from breast cancer cell lines. Surface markers, stemness genes, and tumorigenicity were used to test stem properties. We performed a high-throughput drug screening using these SPS. The effects of candidate compounds were assessed in vitro and in vivo. We successfully generated breast cancer SPS with stem-like properties. These SPS were enriched for CD44^high (2.8-fold) and CD24^low (4-fold) cells. OCT4 and ABCG2 were overexpressed in SPS. Moreover, SPS grew tumors at a density of 10³, whereas an equivalent number of parental cells did not initiate tumor formation. A clinically approved drug, niclosamide, was identified from the LOPAC chemical library of 1,258 compounds. Niclosamide downregulated stem pathways, inhibited the formation of spheroids, and induced apoptosis in breast cancer SPS. Animal studies also confirmed this therapeutic effect. The results of this proof-of-principle study may facilitate the development of new breast cancer therapies in the near future. The extension of niclosamide clinical trials is warranted.

Inhibition of STAT3 by niclosamide synergizes with erlotinib against head and neck cancer

Epidermal growth factor receptor (EGFR) is extensively expressed in head and neck cancer. However, EGFR-targeted therapy has only modest efficacy in head and neck cancer, through mechanisms that are not fully understood. Here, we found that inhibition of EGFR by erlotinib stimulated phosphorylation and activation of STAT3 leading to increased Bcl2/Bcl-XL expression in head and neck cancer cells, which may dampen the therapeutic efficacy of erlotinib against head and neck cancer. Erlotinib-enhanced STAT3 phosphorylation results, at least in part, from suppression of its physiological phosphatase, PTPMeg2. Specific knockdown of STAT3 by RNA interference significantly sensitized head and neck cancer cells to erlotinib treatment. Pharmacological inhibition of STAT3 by niclosamide not only blocked erlotinib-stimulated STAT3 phosphorylation but also synergistically repressed head and neck cancer growth in vitro and in vivo. Combined inhibition of EGFR and STAT3 by erlotinib and niclosamide more effectively induced apoptosis in tumor tissues without toxicity for normal tissues. Based on our findings, treatment with erlotinib combined with niclosamide may offer an effective therapeutic approach to improve the prognosis of head and neck cancer.

Small molecule modulators of Wnt/β-catenin signaling

The Wnt signal transduction pathway is dysregulated in many highly prevalent diseases, including cancer. Unfortunately, drug discovery efforts have been hampered by the paucity of targets and drug-like lead molecules amenable to drug discovery. Recently, we reported the FDA-approved anthelmintic drug Niclosamide inhibits Wnt/β-catenin signaling by a unique mechanism, though the target responsible remains unknown. We interrogated the mechanism and structure-activity relationships to understand drivers of potency and to assist target identification efforts. We found inhibition of Wnt signaling by Niclosamide appears unique among the structurally-related anthelmintic agents tested and found the potency and functional response was dependent on small changes in the chemical structure of Niclosamide. Overall, these findings support efforts to identify the target of Niclosamide inhibition of Wnt/β-catenin signaling and the discovery of potent and selective modulators to treat human disease.

Niclosamide is a proton carrier and targets acidic endosomes with broad antiviral effects

Viruses use a limited set of host pathways for infection. These pathways represent bona fide antiviral targets with low likelihood of viral resistance. We identified the salicylanilide niclosamide as a broad range antiviral agent targeting acidified endosomes. Niclosamide is approved for human use against helminthic infections, and has anti-neoplastic and antiviral effects. Its mode of action is unknown. Here, we show that niclosamide, which is a weak lipophilic acid inhibited infection with pH-dependent human rhinoviruses (HRV) and influenza virus. Structure-activity studies showed that antiviral efficacy and endolysosomal pH neutralization co-tracked, and acidification of the extracellular medium bypassed the virus entry block. Niclosamide did not affect the vacuolar H(+)-ATPase, but neutralized coated vesicles or synthetic liposomes, indicating a proton carrier mode-of-action independent of any protein target. This report demonstrates that physico-chemical interference with host pathways has broad range antiviral effects, and provides a proof of concept for the development of host-directed antivirals.

[Distribution of niclosamide spreading oil on water surface and its efficacy against cercariae of Schistosoma japonicum]

OBJECTIVE

To investigate the distribution and spreading speed of niclosamide spreading oil, as well as its effect against cercariae of Schistosoma japonicum.

METHODS

The foamed plastic with a diameter of 4 mm served as a buoyage, which was placed at the center of the still water surface. The niclosamide spreading oil was dropped at 0.5 cm from the buoyage, the floating distance of the buoyage was observed, and the spreading speed and area of the niclosamide spreading oil were measured. A cylindrical bucket (at a diameter of 40 cm and height of 50 cm) was filled with de-chlorinated water at a temperature of 25 +/- 1 degrees C, and then 60 microl of the spreading oil was dropped at the center of the water surface. At 10 cm and 20 cm from the center, 1 ml water was sampled at water depths of 10, 20, 30, 40 cm and 50 cm, respectively, and the niclosamide concentrations were determined by using high-performance liquid chromatography in each sample. The niclosamide spreading oil was diluted into solutions at effective concentrations of 1.25 mg/L and 0.63 mg/L with ethanol, and then 10 microl of each solution was added to 24-well plates which contained S. japonicum cercariae to yield the niclosamide concentration of 6.25 x 10(-3) mg/L and 3.13 x 10(-3) mg/L per well, respectively. The survival of the cercariae was observed at different time.

RESULTS

The spreading speeds and areas were 59, 55, 71, 90, 111, 122 cm/s and 153 cm/s, and 5.31, 5.89, 7.07, 10.06, 12.56, 15.20 m2 and 16.61 m2, respectively, while dropping 20, 30, 40, 50, 60, 70 microl and 80 microl of the niclosamide spreading oil on water surface. The spreading showed an accelerating trend with the increasing dropping volume, and there was a good linear relationship observed between them. In addition, the spreading area also enlarged with the increase in the dropping volume. After dropping 60 microl of the niclosamide spreading oil on water surface, the peak concentration of niclosamide reached 1.27 mg/L on water surface, and remained more than 0.07 mg/L 2 h later. However, the concentration of niclosamide was all lower than 0.04 mg/L at 10 cm under surface or more. Following the treatment with 6.25 x 10(-3) mg/L of niclosamide spreading oil for 1 min, all the cercariae were dead, while the mortality rates of the cercariae were 0, 1.39%, 13.89%, 19.44%, 43.06%, 69.44% and 79.17% at 1, 2, 3, 5, 10, 20 min and 30 min, respectively, after the treatment with 3.13 x 10(-3) mg/L of the drug.

CONCLUSIONS

The niclosamide spreading oil is fast to spread and is kept retention for a long time on water surface, and exhibits high activity against S. japonicum cercariae, and it can be used for killing the cercariae on water surface and interrupting the transmission of schistosomiasis in the endemic field.

[Effect of niclosamide spreading oil on killing schistosome cercariae]

Dechlorinated water (100 ml, 30 degrees C) was put into a plate (diameter 15 cm), and 1% niclosamide spreading oil 5 microl was added, then a ring of Schistosoma japonicum cercariae were picked up to the plate. The time of killing all the cercariae was observed at three time points (immediately, 24, 48 h), and the dechlorinated water was used as control. The results showed that schistosome cercariae were all killed in three minutes by 1% niclosamide spreading oil at the three time points. The cercaria-killing effects of each time point were not significantly different (F = 0.062, P > 0.05). The cercariae were alive in the control in 48 h.

[Effect of snail control of niclosamide by soil mixing and spraying methods in high dam of terrace]

The snail control efffect of niclosamide by soil mixing and spraying method were compared, and the results showed that the effects of the two methods were similar. Though there was difficulties in getting soil and mixing durg with soil, and the cost was high, the effect of soil mixing method in some special environment such as stone ditches and terraces.

[Studies on standardization of methods for screening molluscicides in laboratory IV sensitivity of Oncomelania snails from different months to niclosamide]

OBJECTIVE

To understand the sensitivity of Oncomelania snails collected from different months to niclosamide, so as to provide the scientific evidence for the standardization of methods for molluscicide screening and efficacy evaluation in laboratory.

METHODS

The snails collected from the marshland of Zhenjiang City, Jiangsu Province month by month from June 2010 to May 2011. After being raised in laboratory for 24 h, the snails were randomly grouped, and then immersed in different concentrations of 50% wettable powder formulation of niclosamide ethanolamine salt at (25 +/- 1) degrees C with a humidity of 60%. The dead snails were identified and counted, and the mortality rate of snails and median lethal concentration (LC50) were calculated.

RESULTS

When the snails were immersed in the solutions of niclosamide at concentrations of more than 0.5 mg/L for 24 h, all the snails collected from different months were dead, while 60%-100% of the snail mortality was achieved for 0.250 mg/L niclosamide, 3%-27% for 0.125 mg/L niclosamide, and 3%-20% for 0.062 5 mg/L niclosamide. When the concentration was lower than 0.032 mg/L, the niclosamide was not toxic to the snails within 24 h. The LC50 value was 0.140-0.209 mg/L for 24 h. When the snails were immersed in the solutions of niclosamide at concentrations of more than 0.5 mg/L for 48 h, all the snails collected from different months were dead, while 90%-100% of the snail mortality was achieved for 0.250 mg/L niclosamide, 3%-57% for 0.125 mg/L niclosamide, 3%-13% for 0.062 5 mg/L niclosamide, and 0-10% for 0.032 mg/L niclosamide. When the concentration was lower than 0.016 mg/L, the niclosamide was not toxic to the snails within 48 h. The LC50 value was 0.112-0.170 mg/L for 48 h. There were no significant differences in the mortality of snails caused by niclosamide treatment observed at 24 and 48 h (P values = 0.374 and 0.267, respectively).

CONCLUSIONS

There are little changes in the sensitivity of snails collected from different months to niclosamide, with minor fluctuations in LC50 values. Such a finding indicates that the snails collected from different months have few effects on screening of molluscicides and efficacy evaluation.