Mechanism study of the molluscicide candidate PBQ on Pomacea canaliculata using a viscosity-sensitive fluorescent probe

PBQ[1-(4-chlorophenyl)-3-(pyridin-3-yl)urea],an enormous potent molluscicide,showed excellent Pomacea canaliculata(P.canaliculata)control activity and low toxicity for other aquatic organisms,but its snail-killing mechanisms are still not fully understood.We employed an optical method to elucidate PBQ action via a novel fluorescent viscosity probe,NCV.As the viscosity in the test solutions increased,compared with that in pure ethanol,a 54-fold fluorescence intensity enhancement of NCV was observed in 310 cP of 90%glycerol.Furthermore,NCV successfully exhibited a selective fluorescence response towards monensin-induced cellular viscosity changes in HepG2 cells.The liver,stomach,and foot plantar of the tested snails were frozen and sectioned for fluorescent imaging experiments after the treatment with different PBQ concentrations over various times.A significant fluorescent increase in the snail's liver was observed upon exposure to 0.75 mg/L PBQ for 72 h,which highlighted an increase in viscosity.Hematoxylin and eosin(HE)staining further supported PBQ-induced liver damage with a viscosity increase in P.canaliculata.Our study provides a new rapid optical visualization method to study the killing mechanisms of PBQ and may help discover new chemicals that control snail populations.

Critical analysis of molluscicide application in schistosomiasis control programs in Brazil

In Brazil,Biomphalaria glabrata,B.tenagophila,and B.straminea are naturally infected by the trematode Schistosoma mansoni,the causative agent of schistosomiasis.Despite decades of governmental efforts through official control programs,schistosomiasis remains an important public health problem in the country:thousands of people are infected with the trematode each year and millions live in endemic areas.The World Health Organization recommends using a combination of molluscicide(niclosamide)and mass chemotherapy to control the transmission of schistosomiasis,with this treatment successfully reducing the morbidity of the disease.In the past,niclosamide has been used in official schistosomiasis control programs in Brazil.However,as B.glabrata recolonizes even after molluscicide application,the use of molluscicides has gradually decreased in the country until they were discontinued in 2002,mainly due to the rising global pressure to preserve the environment and the difficulties of obtaining licenses from the Brazilian Ministry of Environment to use toxic substances in aquatic ecosystems.Therefore,the discovery of new molluscicides,which could be more selective to Biomphalaria species and less harmful to the aquatic ecosystem,is necessary.In addition,political efforts to sensitize funders to provide grants for this field of research are required.In this context,this article aims to make a critical analysis of molluscicide application in schistosomiasis control programs in Brazil.

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

Schistosomiasis is a snail-transmitted infectious disease affecting over 200 million people worldwide.Snail control has been recognized as an effective approach to interrupt the transmission of schistosomiasis,since the geographic distribution of this neglected tropical disease is determined by the presence of the intermediate host snails.In a recent Scoping Review published in Infectious Diseases of Poverty,Coelho and Caldeira performed a critical review of using molluscicides in the national schistosomiasis control programs in Brazil.They also described some chemical and plant-derived molluscicides used in China.In addition to the molluscicides described by Coelho and Caldeira,a large number of chemicals,plant extracts and microorganisms have been screened and tested for molluscicidal actions against Oncomelania hupensis,the intermediate host of Schistosoma japonicum in China.Here,we presented the currently commercial molluscicides available in China,including 26%suspension concentrate of metaldehyde and niclosamide(MNSC),25%suspension concentrate of niclosamide ethanolamine salt(SCNE),50%niclosamide ethanolamine salt wettable powder(WPN),4%niclosamide ethanolamine salt dustable powder(NESP),5%niclosamide ethanolamine salt granule(NESG)and the plant-derived molluscicide“Luowei”.These molluscicides have been proved to be active against O.hupensis in both laboratory and endemic fields,playing an important role in the national schistosomiasis control program of China.Currently,China is transferring its successful experiences on schistosomiasis control to African countries.The introduction of Chinese commercial molluscicides to Africa,with adaptation to local conditions,may facilitate the progress towards the elimination of schisosomiasis in Africa.

Molluscicidal effectiveness of Luo-Wei,a novel plant-derived molluscicide,against Oncomelania hupensis,Biomphalaria alexandrina and Bulinus truncatus

Background:Control of snail intermediate hosts has been proved to be a fast and efficient approach for interrupting the transmission of schistosomiasis.Some plant extracts have shown obvious molluscicidal activity,and a new compound Luo-Wei,also named tea-seed distilled saponin(TDS),was developed based on the saponins extracted from Camellia oleifera seeds.We aimed to test the molluscicidal activity of 4%TDS against the intermediate host snails in China and Egypt,and evaluate its environmental safety to non-target organisms.Methods:In the laboratory,Oncomelania hupensis,Biomphalaria alexandrina and Bulinus truncatus were exposed to 4%TDS,and the median lethal concentration(LC5o)was estimated at 24,48 and 72 h.In the field,snail mortalities were assessed 1,2,3 and 7 d post-immersion with 2.5 g/m34%TDS and 1,3,7 and 15 d post-spraying with 5 g/m24%TDS.in addition,the acute toxicity of 4%TDS to Japanese quail(Coturnixjaponica),zebrafish(Brachydanio rerio)and freshwater shrimp(Macrobrachium nipponense)was assessed by estimations of LC5o or median lethal dose(LD5o).Results:In the laboratory,the LC5o values of 4%TDS for O.hupensis were 0.701,0.371 and 0.33 mg/L at 24,48 and 72 h,respectively,and 4%TDS showed a 0.33 mg/L 24 h LC5o against B.alexandrina,and a 1.396 mg/L 24 h LCs0 against B.truncatus.Across all study regions,the pooled mortalities of O.hupensis were 72,86,94 and 98%at 1,2,3 and 7 d,following field immersion of 4%TDS at a dose of 2.5 g/m3,and were 69,77,85 and 88%at 1,3,7 and 15 d,following field spraying at 5 g/m2,respectively.4%TDS had moderate toxicity to Japanese quail(7 d LD5o>60 mg/kg)and to shrimp(96 h LCs0=6.28 mg/L;95%CI:3.53-11.2 mg/L),whereas its toxicity to zebrafish was high(96 h LCso--0.15 mg/L;95%CI:0.14-0.17 mg/L).Conclusions:4%TDS is active against O.hupensis,B.alexandrina and B.truncatus under laboratory and field conditions,and it may be a candidate molluscicide of plant origin.

Effects of the molluscicide can didate PPU06 on alkaline phosphatase in the golden apple snails determined using a near-infrared fluorescent probe

We constructed a reaction-based near-infrared fluorescent probe(Niap) to specifically identify alkaline phosphatase(ALP) with fast red fluorescence enhancement.Based on the positive concentrationdependent manner between the fluorescent intensity of the Niap and ALP,probe Niap was used to study the ALP enrichment and variation in golden apple snails(Pomacea canaliculata) exposed to the molluscicide candidate PPU06.After treatment with different concentrations of PPU06 over various times,three organs of the surviving snails,liver,stomach and plantaris,were frozen and sectioned for fluorescent imaging experiments.With increased PPU06 concentration,red fluorescence substantially increased in the liver and reached a maximum within 24 h when the PPU06 co ncentration was 0.75 mg/L.No obvious changes in the stomach or foot plantaris were found.It showed PPU06 caused liver injury and stimulated the increase of ALP in the liver of P.canaliculata.This study demonstrates a rapid ALP fluorescent identification method that can be used to study the effects of PPU06 on P.canaliculata.It also provides optical evidence that may aid in the discovery of new chemistry for snail control.

Laboratory assessment of the molluscicidal and cercariacidal activities of Balanites aegyptiaca

Objective:To assess the molluscicidal and cercariacidal activities of aqueous extracts of Balanites aegyptiaca(B.aegyptiaca)against EthiopianBiomphalaria pfeifferi(B.pfeifferi),Lymnaea natalensis(L.natalensis)and Schistosoma mansoni(S.mansoni)cercariae.Methods:Extracts of seeds,endocarp,mesocarp,and fruit of B.aegyptiacawere tested for their activities against adultB.pfeifferiandL.natalensis.The cercariacidal activity of the seeds of the plant was also evaluated againstS.mansoni.Bioassays were carried out following the methods recommended by WHO.Snail mortalities were compared between each plant part and snail species,and LC50and LC90values for the plant parts tested were computed.The cercariacidal activity of the plant was assessed by exposing the mice to the cercariae pre-exposed to aqueous extract of B.aegyptiacaseeds.Results:For the molluscicidal activities of seeds,endocarp,mesocarp and whole fruit,the LC50values againstB.pfeifferiwere 56.32,77.53,65.51 and 66.63 mg/L,respectively,while the respective LC90values were 77.70,120.04,89.50 and 97.55 mg/L.Similarly,the LC50values for the seeds,endocarp,mesocarp and whole fruit againstL.natalensiswere 80.33,92.61,83.52 and 87.84mg/L,respectively,while the respective LC90values were 102.30,138.21,115.42 and 127.69 mg/L.B.pfeifferiwere found to be more susceptible toB.aegyptiacathanL.natalensis.S.mansoni cercariae exposed to 15 mg/L of extract of seeds were incapable of infecting mice.The mean egg load of tissue was reduced in mice infected with the cercariae exposed to 5 and 10 mg/L of the extract.Conclusions:The aqueous extracts of different parts ofB.aegyptiacaexhibited reasonable molluscicidal activity againstB.pfeifferiandL.natalensis,as well as cercariacidal activity againstS.mansonicercariae.However,comprehensive laboratory evaluation is recommended prior to field tests of the plant parts since their impact on other aquatic biota is not known.

Molluscicidal activities of green-synthesized Alstonia congensis silver nanoparticles

Objective:To evaluate the efficacy of Alstonia congensis green-synthesized nanoparticles as a molluscicide against snail hosts of trematodes.Methods:The ethanolic leaf extract of Alstonia congensis was used to synthesize silver nanoparticles.The formulation was characterized by Fourier transform infrared spectroscopy,X-ray powder diffraction,and scanning electron microscope/energy-dispersed X-ray.The ovicidal and molluscicidal activities of the Alstonia congensis extract and its nanoparticles were tested against Physa acuta and Bulinus forskalii at different concentrations.Results:The green-synthesized nanoparticles inhibited embryonic development within the egg masses of the two snails in all the tested concentrations.Alstonia congensis extract did not show molluscicidal properties against adult Physa acuta but showed a very weak activity against Bulinus forskalii.Moreover,the synthesized nanoparticles showed significantly high molluscicidal activity against adult snails within 5-40 min of exposure in a concentration-dependent manner(P<0.05).Conclusions:The Alstonia congensis-based nanoparticles show molluscicidal activities against adults and embryos of Physa acuta and Bulinus forskalii,and can be further explored as a potent molluscicide for the control of intermediate host of trematode parasites.

Molluscicidal effect of green synthesized silver nanoparticles using Azadirachta indica on Biomphalaria alexandrina snails and Schistosoma mansoni cercariae

Objective:To assess the molluscicidal effect of the eco-friendly green synthesized neem silver nanoparticles(neem-Ag NPs)against Biomphalaria alexandrina,the snail intermediate host for Schistosoma mansoni,and their cercaricidal potential.Methods:Methanol extracts from neem fruits were used for green synthesis of neem-Ag NPs.The neem-Ag NPs were characterized using UV-visible absorption spectra,dynamic laser light scattering technique,and transmission electron microscopy.The potential molluscicidal effect against adult and juvenile Biomphalaria alexandrina and the effect of the sub-lethal concentration on hatching of snail eggs and Schistosoma mansoni cercariae were evaluated.Results:The surface plasmon resonance of neem-Ag NPs showed a sharp absorption peak atλ_(max)=518 nm together with multiple peaks.The hydrodynamic diameter was(77.15±34.53)nm,the polydispersity index(0.338±0.000)and the zeta-potential-14.07 mV.Moreover,transmission electron microscopy showed that the average size of the nanoparticles was(27±2)nm.Agglomeration was evident and a light-colored capping layer could be seen coating the nanoparticles.Juvenile snails(LC_(50):0.83 ppm)were more susceptible to neem-Ag NPs than adults(LC_(50):1.07 ppm).In addition,neem-Ag NPs and neem at LC_(50)concentrations inhibited the egg-hatching of snails and showed cercaricidal activity in a time-dependent manner.Conclusions:Neem-Ag NPs have lethal activities against Biomphalaria alexandrina snails and their eggs,as well as Schistosoma mansoni cercariae.Hence,neem-Ag NPs could be a potential agent to control schistosomiasis.

Synthesis of New Fluorine/Phosphorus Substituted 6-(2’-Amino Phenyl)-3-Thioxo-1,2,4-Triazin-5(2H, 4H)One and Their Related Alkylated Systems as Molluscicidal Agent as against the Snails Responsible for Bilharziasis Diseases

New fluorine substituted 6-(5’-fluoro-2’-triphenylphosphiniminophenyl) 3-thioxo-1,2,4-triazin-5 (2H, 4H) one (2) was obtained via Wittig’s reaction of the corresponding 6-(5’-fluoro-2’-amino-phenyl)-3-thioxo-1,2,4-triazinone (1). Behavior of compound 2 towards alkylating agents and/or oxidizing agents was studied were, N-hydroxyl (3), Mannich base (4,5), S-alkyl (6,7,8) and thiazolo [3,2-b][1,2,4] triazinones (10-14) and or 3-disulfide (18), 3-sulfonic acid 19 and 1,2,4-triazin-3,5-Dionne (20) derivatives obtained. Structures of the new products are established by elemental and spectral data. The new targets obtained screened as Molluscicidalagents against Biomophlaria Alexandrina snails responsible for Bilharziasis diseases, in compare with Baylucide as standard drug.

Synthesis of Some More New Fluorinated 1,2,4-triazino[3,4-b][1,3,4]Thiadiazolonesand Their Molluscicidal Against Selective Snails - Part I

Some more new fluorinated 1,2,4-triasino[3,4-b][1,3,4]thiadiazolones （6-9 and 11-16） have been synthesized from cyclocondensation of 5-hydrazino-2-（4＇-fluorophenyl）-1,3,4-thiadiazole with bifunctional oxygen and halogen compounds. Structures of the products have been deduced from their elemental, chemical and spectral data （UV, IIL 1H/13C NMR （nuclear magnetic resonance） and mass）. All the new compounds evaluated as molluscicidal against towards snails which responsible for Bilharziasis diseases.

Reaction of Oncomelania Hupensis to the Allelopathic Triterpene Sapogenin from Nerium Indicum

This paper has analyzed allelopathic effects ofNerium indicum on Oncomelania hupensis through triterpene sapogenins, a potential molluscicide. The snails were treated under six various concentrations （0, 20, 40, 60, 80, 100 mg/L） of triterpene sapogenins and five periods （1, 2, 3, 4, 5 days）. The mortality of snails was positively correlated with the concentration of triterpene sapogenins and exposure time. The results ofprobit analysis showed that the LD50 （Lethal Dose, 50%） oftriterpenoid saponins from N. indicum by immersion for 2, 3, 4, 5 days were 78.31, 30.26, 20.50, 14.19 mg/L, respectively. And the corresponding 95% confidence intervals were 63.60-108.19, 9.49-44.42, 2.86-30.90, 0.23-22.79 mg/L, respectively. The observations of both scanning electron microscope and transmission electron microscope proved that 40 mg/L triterpene sapogenins could cause apparent damage to the structure of soft tissue, liver and intestine of O. hupensis. The esterase （EST） isozyme electrophoresis in liver of O. hupensis treated by 40 mg/L of the concentrations lixivium of the triterpene sapogenins from N. indicum was analyzed for 24, 48, 72, 96, 120 h, respectively. The activity of enzyme was higher than control water group after been treated up to 24-48 h, and then lowered and disappeared after 72 h. It was implicated that the extracted triterpene sapogenin from N. indicum were promising for controlling the snail, which were also providing the foundation for constructing plant community of oleander to control O. hupensis.

Molluscicidal effect of Achyranthes aspera L.(Amaranthaceae)aqueous extract on adult snails of Biomphalaria pfeifferi and Lymnaea natalensis

Background:Intestinal schistosomiasis caused by Schistosoma mansoni is a wide spread disease in most parts of Ethiopian highlands.Snail control is one major strategy in schistosomiasis control.The use of molluscicidal plant products is becoming interesting due to their environmental friendliness,accessibility and easy application.This research is aimed to evaluate the molluscicidal effect of Achyranthes aspera on Biomphalaria pfeifferi and Lymnaea natalensis snails,which are of great medical and veterinary importance in Ethiopia.Methods:Adult B.pfeifferi snails were exposed to the various concentrations of A.aspera aqueous leaf extract for 24,48 and 72 h.Similarly,adult L.natalensis snails were exposed to the extract for 24 h.Mortality data were analyzed using probit regression model.Phytochemical content of the plant was analyzed using standard screening methods.Results:The plant’s molluscicidal effect on the two snail species was demonstrated.The 24 h LC50 and LC90 values against L.natalensis were 69.5 and 93.9 ppm respectively.In the 24,48 and 72 h exposure of B.pfeifferi,the LC50 values were 72.4,69.9,64.7 ppm and the LC90 were 96.5,93.8,92.8 ppm,respectively.The phytochemical screening tests indicated presence of saponins.Conclusion:From the findings of this study,A.aspera has a molluscicidal potential.The result provides a useful foundation for further in-depth studies to ensure its wider applicability in different water bodies and evaluate its toxic effects on non-target species.

Molluscicidal activity of chlorophyll extraction against the freshwater snails

Objective:To evaluate the molluscicidal activity of chlorophyll extract as a photodynamic substance against the snails Lymnaea stagnalis,Biomphalaria spp.and Physa marmorata.Methods:Chlorophyllin was extracted from deep-frozen spinach.Snails were incubated in chlorophyllin containing water with 2.5,5.0,10.0 and 15.0μg/mL.All samples were kept in darkness overnight for incubation.After incubation,three samples were irradiated with simulated solar radiation for 3 h.After irradiation,the vitality of the organisms was determined.Results:The photodynamically active chlorophyllin,at low concentrations,was able to kill snails within a few hours under exposure of solar radiation.Besides,it had a killing effect by about 70%and 100%on the snails’eggs and the newly hatched snails,respectively,after 3 h exposure to solar radiation.Conclusion:The derivates of chlorophyll was a very interesting substance for photodynamic freshwater snail control.Hence,it might be a promising and cheap new strategy which probably had the potential to replace the synthetic molluscicides for snail control.

SWOT analysis on snail control measures applied in the national schistosomiasis control programme in the People’s Republic of China

Background:Snail control is an important component in the national schistosomiasis control programme in China,by application of chemical molluscicides,forestry projects,agriculture projects and water conservancy projects in recent decades.However,there are still wide areas of snail inhabited in China which remains a great challenge to achieve the goal of schistosomiasis elimination by 2025.Therefore,a SWOT(strengths,weaknesses,opportunities and threats)analysis on snail control measures is required for precision schistosomiasis control.Methods:The SWOT approach,which is a well-known structured analysis tool,was used to identify and evaluate the specific characteristics of four types of snail control measures in China,including chemical mollusciciding,forestry,agriculture,and water conservancy projects.The analysis were carried out based on the information collection from literature review,of research papers,books,annual report database of national schistosomiasis control programme in China,reports from the academic forums,and so on.Results:For chemical mollusciciding,application strategy needs to focus on specific local settings,such as stage of schistosomiasis control,environmental factors,and limitations from external policies and internal deficiencies.Regarding forestry projects,the optimal strategies are to cooperate with other national forestry programmes to share the investment costs and pay attention on wetland protection.In agriculture projects,it is necessary to develop related cash crop industries and combine with national farmland consolidation projects simultaneously to increase the total economic benefits.Concerning water conservancy projects,the main purpose is to control snail migration from snail area to snail-free areas nationwide.Conclusions:Integrated strategies for various measures application and a top-level designed cooperation mechanism will be the necessary to eliminate snail and schistosomiasis in China.