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Schistosomiasis is a public health problem in many developing countries. The mollusc Biomphalaria glabrata is the most important vector of Schistosoma mansoni in South America. The population control of this vector to prevent the spread of schistosomiasis is currently done with the application of highly toxic molluscicide to the environment. The screening of substances in sublethal concentrations that have deleterious effects on physiological parameters is very relevant for the control of schistosomiasis, since the effectiveness of disease prevention increases if it acts on population control of the vector and on reproduction and elimination in S. mansoni cercariae. The objective of this study was to evaluate the reproductive parameters (fecundity and fertility), intra-mollusk effect (sporocysts I (72 h) and II (14 days after)) on the development of cercariae of S. mansoni and the immune cell profile of B. glabrata exposed to sublethal concentrations (LC25 - 0.5 µg/mL and LC50 - 0.92 µg/mL) of the usnic acid potassium salt (potassium usnate). LC 25 and LC 50 significantly reduced (p

To explore a new molluscicide with dual effects of fertilization and molluscicidal activity, an organic-inorganic compound fertilizer molluscicide was prepared by mixing the water extract (or powder) of Arisaema erubescens tubers with nitrogen fertilizer, phosphate fertilizer, potash fertilizer, and three mixed fertilizers (hereinafter referred to as ANF, APF, AKF and ACF, respectively). Leaching using the mixture was performed to test for molluscicidal activity, and indoor rice germination, seedling growth, and pot experiments were monitored. ANF exhibited superior molluscicidal activity, with respective 24-h and 48-h Oncomelania mortality rates significantly increased, reaching up to 67.7% and 92.3%. ANF, APF, and AKF significantly promoted rice germination and growth of rice, with ANF showing superior effects. The respective 3-day and 5-day germination rate of rice seeds treated with ANF significantly increased by 25% and 21% relative to that of the control group, and the respective 10-day and 20-day growth length of rice seedlings (aboveground part) increased by 106.2% and 33.2%. A positive correlation between ACF molluscicidal activity and concentration and treatment time were observed. The Oncomelania mortality rate at 48 h after treatment with a low ACF concentration (0.25 g/L) was 70.7%, whereas that at 24 h after treatment using a higher concentration (0.5 g/L) was 80.7%. ACF promoted rice seed germination and seedling growth, whereas inhibitory effects were observed using a high ACF concentration. Therefore, the combined application of A. erubescens and chemical fertilizers not only enhances molluscicidal activity, but also promotes rice growth, with the combined application of A. erubescens and nitrogen fertilizer and mixed fertilizer showing superior dual effects (molluscicide and fertilization).

The molluscicidal action of essential oils have been attributed to the most prevalent terpene compounds. However, molluscicidal properties, mode of action, and toxicity to non-target organisms remain unclear. In this study, the molluscicidal potential of four monoterpenes (camphor, thymol, α-pinene, and 1,8-cineole) against the snail Biomphalaria glabrata, an intermediate host of Schistosoma mansoni, was analyzed. The molluscicide activity of each monoterpene was assessed by the standardized test of the World Health Organization (WHO) and the monoterpenes considered active against B. glabrata were analyzed as inhibitors of the enzymatic activity of acetylcholinesterase (AChE) extracted from snails. In addition, acute toxicity to non-target organisms was assessed against Danio rerio fish. The results show that camphor and 1,8-cineole monoterpenes did not induce snail mortality. Thymol and α-pinene were active against B. glabrata, inducing mortality in concentration-dependent patterns and showing a lethal effect in concentrations compatible with that recommended by the WHO (LC90 of 7.11 and LC90 10.34 μg ∙ mL−1, respectively). The toxic action of thymol and α-pinene on snails indicates that these monoterpenes may account for or largely contribute to the molluscicidal activity of essential oils that contain them as major compounds. Thymol and α-pinene inhibit the AChE of B. glabrata at concentrations higher than those used in the molluscicide test. These monoterpenes show low toxicity to non-target organisms compared to the commercial molluscicide niclosamide. Knowledge about monoterpene toxicity against B. glabrata contributes to its potential use in molluscicidal formulations and in alternatives to the control of snails that host intermediate S. mansoni, a crucial action in the prevention and transmission of schistosomiasis, a neglected tropical disease.

Schistosomiasis continues to pose significant public health problems in many developing countries. Mass drug administration (MDA) is the most adopted control option but there is increasing evidence for the development of praziquantel-resistant Schistosoma strains. This shortcoming has necessitated the search for other effective methods for the control of schistosomiasis. The breaking of Schistosoma transmission cycles through the application of molluscicides into snail infested freshwater bodies has yielded positive outcomes when integrated with MDA in some countries. However, few of such effective molluscicides are currently available, and where available, their application is restricted due to toxicity concerns. Some nanotized particles with molluscicidal activities against the different stages of snail intermediate hosts of schistosomes have been reported. Importantly, the curcumin-nisin nanoparticle synthesized by our group was very effective and it showed no significant toxicity in a mouse model and brine shrimps. This, therefore, offers the possibility of developing a molluscicide that is not only safe for man but also is environmentally friendly. This paper reviews nanoparticles with molluscicidal potential. The methods of their formulation, activities, probable mechanisms of actions, and their toxicity profiles are discussed. More research should be made in this field as it offers great potential for the development of new molluscicides.

Oncomelania hupensis is the intermediate host of Schistosoma japonicum, one of the Schistosoma species that can cause human schistosomiasis. Molluscicidal treatment remains the primary means to control snail. Niclosamide is the only molluscicide recommended by the World Health Organization, and it has been used throughout schistosomiasis-endemic areas in China for almost 30 years. In our previous studies on transcriptomics, morphology, and enzymology of snails after molluscicidal treatment, two effective molluscicides were used, 50% wettable powder of niclosamide ethanolamine salt (WPN) and a new molluscicide derived from niclosamide, the salt of quinoid-2', 5-dichloro-4'-nitro-salicylanilide (LDS, simplified for Liu Dai Shui Yang An). Genes involved in cell structure mintenance, inhibition of neurohumoral transmission, and energy metabolism showed significant differential expression after molluscicide treatments. Damages in the structure of liver and muscle cells were accompanied by inhibited activities of enzymes related to carbohydrate metabolism and energy supply. This study was designed to clarify the dynamic metabolic process by metabonomics, together with the previous transcriptomic and enzymological profiles, to identify potential metabolite markers and metabolism pathways that related to the toxic mechanism of the molluscicide. In total, 56 metabolites were identified for O. hupensis, and 75% of these metabolites consisted of amino acids and derivatives, organic acids, and nucleic acid components. The concentration of glucose, maltose, succinate, choline, and alanine changed significantly after molluscicide treatments. These changes in metabolites mainly occurred in the process of carbohydrate metabolism, energy metabolism, and amino acid metabolism, primarily related to glycolysis/gluconeogenesis, oxidative phosphorylation, and transamination by KEGG pathway identification. Most of the identified pathways were also related to those differentially expressed unigenes and observed enzymes from our previous studies. Inhibited aerobic respiration and oxidative phosphorylation, and energy deficiency were implied further to be the leading causes of the final death of snails after molluscicide treatments. The hypothesised mathematical model in this study identified the rational hysteresis to explain the inconsistency of responses of unigenes, enzymes, and metabolites to molluscicide treatments. This study contributes to the comprehensive understanding of the molluscicidal mechanism in the metabolic process and this could assist in improving existing molluscicide formulations or development of new molluscicides.

Silver nanoparticles (Ag NPs) have been applied in several commercial products due to their antimicrobial properties, while their molluscicide properties, mode of action and toxicity to snail species remain unclear. In this study, the comparative toxicity of polyvinylpyrrolidone (PVP)-functionalized Ag NPs and their dissolved counterpart (Ag ions) was analyzed during the early developmental stages of the freshwater snail Biomphalaria glabrata, intermediate host of Schistosoma mansoni. Ag NPs were synthesized and characterized by multiple techniques, and the snail embryotoxicity was analyzed in terms of mortality, hatching, developmental stages and morphological alterations, while the acute toxicity to newly-hatched snails was analyzed by mortality and behavioral impairments. Results showed that both Ag forms induced mortality, hatching delay and morphological alterations (especially hydropic abnormalities) in snail embryos in a concentration and exposure time dependent patterns. Ag NPs showed low embryotoxic effects and similar toxicity for newly-hatched snails when compared to their dissolved counterparts, indicating that the nanotoxicity was dependent of snail developmental stages. The knowledge about the Ag NP toxicity to different early development stages of B. glabrata contributes to its potential use as molluscicide and control of neglected tropical diseases, including schistosomiasis.

The snail Biomphalaria glabrata is the most important vector for Schistosoma mansoni. Control of this vector to prevent the spread of schistosomiasis is currently performed with the application of a niclosamide molluscicide, which is highly toxic to the environment. Screening of substances that show embryotoxic molluscicidal potential as well as have detrimental effects on cercariae is very relevant for the control of schistosomiasis, as the efficacy of prevention of the disease is increased if it acts as a molluscicide as well as on the cercariae of S. mansoni. The aim of this work was to evaluate the effect of potassium usnate derived from usnic acid on different stages of embryonic development of B. glabrata and on S. mansoni cercariae. After 24 h of exposure, potassium usnate showed embryotoxic activity across all embryonic stages. The values obtained from the LC50 for the embryonic stages were the following: blastula 5.22 μg/mL, gastrula 3.21 μg/mL, trochophore 3.58 μg/mL, veliger 2.79, and hippo stage 2.52 μg/mL. Against S. mansoni cercariae, it had LC90 and 100% mortality at concentrations of 2.5 and 5 μg/mL in 2 h of exposure. In conclusion, this is the first report of potassium usnate toxicity on the embryonic stages of B. glabrata and cercariae of S. mansoni, and this study shows the potassium usnate as a promising agent for the control of mansoni schistosomiasis.

The prevalence of Schistosoma mansoni infection in Venezuela has changed from high to low due mostly to successful control activities, including mass chemotherapy and molluscicide applications. This study examined the impact of mass chemotherapy on S. mansoni transmission and risk factors for infection 12 years after administration of praziquantel in Venezuela. Two relatively isolated rural communities were studied, one with snail control (Manuare) and the second without (Los Naranjos). A cross-sectional survey of randomly selected households included 226 (Manuare) and 192 (Los Naranjos) consenting participants. S. mansoni prevalence was determined using a combination of coprological (Kato-Katz) and serological (circumoval precipitin test, alkaline phosphatase immunoassay and Western blot) tests. Data on epidemiological and socioeconomic risk factors were obtained through individual structured interviews. Univariate analysis and multivariate logistic regression models identified independent risk factors for infection. Water sites were examined for the presence of Biomphalaria glabrata snails. Only one participant was positive by coprology. The overall prevalences according to the combined tests were 32.7% in Manuare and 26.6% in Los Naranjos. Lower prevalences (12.7% in Manuare and 13.2% in Los Naranjos) were found in children12 years of age representing those born after mass chemotherapy. Social demographic variables associated with infection in both communities were older age (25 years), contact with specific water sites, and being a farmer/non-specialised worker. Mass treatment with praziquantel applied once to endemic communities led to an important and long-lasting sustained reduction of S. mansoni infections independent of the application of snail control. A degree of low active transmission of S. mansoni persisted in the treated areas which was associated with similar factors in both communities.

Schistosomiasis is promoted for species from Schistosoma genus affecting over 200 million people worldwide. Molluscicides are an efficient method to control this disease, being able to reduce intermediate host snail Biomphalaria glabrata number. In function of resistance cases using niclosamide, natural products are promisors to discover new drugs. Manilkara subsericea is endemic to Brazilian sandbanks of Rio de Janeiro State and wide ranges of biological activities. However, there is no studies evaluating its effects as molluscicidal agent. We tested crude extract from leaves of M. subsericea molluscicidal action, as well it ethyl-acetate fraction and isolated substances against B. glabrata. M. subsericea leaves crude extract and ethyl acetate fraction induced 80±4.13% and 86.66±4.59% mortality of adult snails at concentrations of 250ppm after 96h, and their LD50 values were 118.7±1.62 and 23.41±1.15ppm respectively. Isolated substances from M. subsericea were also considered active. Quercetin, myricetin and ursolic acid, at concentration of 100ppm (96h), were able to induce mortality levels of 100%, 80% and 53.33%, respectively. Our results suggest that M. subsericea can be considered promising as a molluscicide agent.

This study reports the molluscicidal activity of usnic acid isolated from Cladonia substellata Vanio (lichen) on embryos at various stages of development and in adult mollusks of Biomphalaria glabrata. The toxicity of usnic acid was also evaluated through Artemia salina larvae mortality. Usnic acid was extracted with diethyl ether, isolated, purified, and its structure confirmed by analyzing the spectra of proton nuclear magnetic resonance. LC90 for 24 h of exposure were 1.62, 4.45, 5.36, and 4.49 μg mL−1 for blastula, gastrula, trocophore, and veliger embryonic stages, respectively, and 3.45 μg mL−1 for adult snails; LC50 of usnic acid against A. salina was 2.46 μg mL−1. LC90 assessed 7 days after exposure was 2.56 μg mL−1 for adult mollusks. In conclusion, these findings demonstrate that under laboratory conditions usnic acid has teratogenic and molluscicide potential to control the aquatic snail B. glabrata and may prove to be a promising candidate in the search for new molluscicide agents, but further detailed studies on its molluscicidal effect and possible environmental effects are needed.

Snail control is a key link in schistosomiasis control, but no unified methods for eliminating snails have been produced to date. This study was conducted to explore an engineering method for eliminating Oncomelania hupensis applicable to urban areas. The engineering specifications were established using the Delphi method. An engineering project based on these specifications was conducted in Hankou marshland to eliminate snails, including the transformation of the beach surface and ditches. Molluscicide was used as a supplement. The snail control effect was evaluated by field investigation. The engineering results fulfilled the requirements of the design. The snail density decreased to 0/0.11m2, and the snail area dropped to 0m2 after the project. There was a statistically significant difference in the number of frames with snails before and after the project (P

Since the establishment of the Rahad Irrigation Scheme in 1979, the prevalence of schistosomiasis has increased to high levels in some villages despite the efforts of the Blue Nile Health Project to prevent this. Although a programme of focal snail control has been implemented since 1979, when the first intermediate host snails were detected, infected snails are abundant in human water contact sites near villages where transmission of both S. mansoni and S. haematobium takes place. The objective of the present study was to assess the feasibility and effectiveness of the focal snail control operations in irrigation canals, in terms of reductions in snail density and repopulation rates of treated sites. The efficacy of focal mollusciciding was evaluated by (1) evaluation of the routine molluscicide operation done by the Blue Nile Health Project, (2) experimental application of various dosages of the molluscicide and (3) study of snail repopulation rates. Efficiency was measured by mortality among caged snails placed in the target stretch and from pre-and post-treatment counts of relative snail densities. The short-time application of niclosamide can be very effective in reducing the density of the intermediate host snails in the target stretch of canal. An efficient exposure seems to be approximately 3 ppm (a.i.) for 30–40 min when water flow is slow, while 1 ppm is efficient when water velocity is very slow, i.e. less than 0.04 m s−1, and 0.6 ppm is efficient when the water is virtually stagnant. Turbidity seems not to impair the effect of the treatment and vegetation does not reduce the efficiency of niclosamide, provided the current speed is low and the chemical is applied to the entire width of the canal. However, the results also clearly demonstrate some of the shortcomings of the standard procedure of niclosamide application. A high water velocity and discharge will rapidly wash the chemical through the target canal stretch and the snails will be exposed only for a short period if the routine procedure is followed. In addition, the chemical will not mix sufficiently with water within stands of aquatic macrophytes. Recolonization of treated canal stretches is fast, especially during the irrigation period when water velocities are high and juvenile snails are abundant. Snail density may attain pretreatment levels three weeks after an effective application. Since the routine procedure is most effective at low current speeds, it is suggested that water velocity could be controlled during the application in coordination with the Irrigation Department.

Several field experiments were carried out in Senegal to evaluate the molluscicidal activity of Ambrosia maritima L. Applications of 400 mg L −1 of dry leaves of the plant in creeks of the Lampsar river did result in a reduction of Bulinus spp of 54–56% 2 weeks after treatment. Treatment of a closed irrigation canal caused a reduction of the density of Biomphalaria pfeifferi up to 77% 2 weeks after the application of 150 mg L −1 and 300 mg L −1 . In both trials, however, a quick increase in the snail density was observed after treatment. It is concluded that the large amounts of crude plant material required to achieve snail reductions of less than 80% compromise the use of A. maritima in schistosomiasis control programmes.

The aim of this work was to analyze the content of total protein and nitrogen degradation products in Biomphalaria glabrata infected with Schistosoma mansoni and exposed to Euphorbia splendens var. hislopii latex. The LC(50) of this latex was 1.0mg/l. Concentrations of uric acid, urea and total proteins were determined in the hemolymph of B. glabrata infected with five S. mansoni miracidia and exposed to a sublethal concentration of E. splendens var. hislopii latex for 24h. The exposure to this molluscicide caused total depletion of the alterative sources of energy (total proteins) and significant variation in the nitrogen degradation products. The urea content increased while the uric acid level decreased. These results reflect a disturbance in the snails regulation of their metabolism due to intoxication caused by the latex exposure.

Under laboratory conditions, latex from Euphorbia splendens has shown promise as a plant molluscicide for control of Biomphalaria species, intermediate hosts for Schistosoma mansoni. The purpose of this study was to evaluate its efficiency under field conditions. Application of filtered latex at 12 ppm to one stream in an endemic rural area in Minas Gerais state, Brazil, in September 1995, did result in a reduction in snail density as compared to an untreated stream but the snail population recovered quickly. However, two applications with a two-week interval of unfiltered E. splendens latex at 5 ppm in November 1996 in the same stream resulted in complete disappearance of B. glabrata and snails did not reappear until the 14th month after the applications. In the control stream, without treatment, the snails were found during all months. Laboratory studies confirmed that unfiltered latex is a more potent molluscicide than filtered latex. Considering the advantages of the latex such as its low toxicity to other aquatic animals and its photobiodegradability, as well as the simple method of application, this natural product is promising as an effective molluscicide.

Laboratory studies were conducted to evaluate the molluscicidal properties of three Saudi Arabian Euphorbiales. The results showed that the methanol extract of Euphorbia schimperiana has a high molluscicidal potency. The activity remains stable over a wide range of temperature and pH values, in the presence of organic and inorganic substrates and after exposure of the solutions to ultraviolet radiation.

In Morocco, the implementation of new irrigation schemes resulted in the introduction of schistosomiasis haematobium to new areas. Canal structures (especially syphon boxes) were found to be favourable habitats for Bulinus truncatus and they constitute important transmission sites. Three methods for snail control in these syphon boxes were assessed in the Tessaout-Amont irrigation scheme. Molluscicide (niclosamide) application resulted in a pronounced reduction in the snail population density, but snails started to recolonise the sites a few months later. Regular brushing of the inner sides of the syphon boxes and covering the syphon boxes, so as to exclude light, resulted in significant reductions in snail numbers. However, the latter methods were not as efficient as the molluscicide.

Dried leaf material of a Mexican plant, Agave attenuata, was found to be highly toxic to the target snail, Bulinus africanus, intermediate host of Schistosoma haematobium in South Africa. The molluscicidal potency of the plant underwent seasonal variation, but remained stable over a range of pH values, after exposure to sunlight and organic matter, and during dry storage. It was unstable in aqueous suspension. The toxicity of the molluscicide to crop plants, invertebrates, fish and mammals was lacking or low. Given these properties, A. attenuata may provide a substitute for niclosamide and be used safely for snail control by rural communities.

Apodytes dimidiata has recently come to the fore as a potential plant molluscicide for schistosomiasis control in rural communities in South Africa. Prior to field applications of its leaves and extract to waterbodies, selected acute and sub-acute mammal toxicity tests were conducted in accordance with the Organisation of Economic Cooperation and Development (OECD) Guidelines to identify any potential hazards that might arise form the plant's use. Acute and sub-acute mammal toxicity test results classified A. dimidiata as non-toxic and non-irritating. Based on this toxicity evaluation, the dried leaf material and aqueous extracts of this plant are considered safe for use in preliminary field trials.

The crude aqueous leaf extract of a South African tree, Apodytes dimidiata , has been identified as a potential molluscicide for snail control in anti-schistosomiasis programmes in rural communities. Before preliminary field trials could be implemented its acute toxic effects on two non-target organisms were examined in accordance with the OECD guidelines to identify any potential hazards that might arise from the plant's use. Laboratory results showed that working molluscicidal concentrations of the plant extract were non-toxic to earthworms suggesting that it is non-hazardous to soil-dwelling fauna. The plant extract proved toxic to fish and was assigned the risk phrase `harmful to the aquatic environment' according to the EEC classification scheme. Based on these toxicity evaluations, aqueous extracts of A. dimidiata are considered safe for use in preliminary field trials.

Phytolacca dodecandra, a plant with berries of a known molluscicidal potency, was cultivated in Chiweshe. Studies on the snail population density of Bulinus globosus and Lymnaea natalensis as well as schistosome infection rates in the former were carried out in two streams, in one of which a water extract of P. dodecandra berries was applied in late April and May 1987. Snail sampling was carried out twice a month from April 1986 to April 1988, that is for 12 months prior to and after the mollusciciding exercise. B. globosus snails obtained from both streams were examined for infection by cercarial shedding before they were returned to their sites of collection. The 8-h water extract of P. dodecandra was applied to human watercontact points. The two applications were aimed at achieving a concentration of 50 mg/1. No snails were recovered from the experimental sites for a period of 7 months after the mollusciciding exercise. Snails were recovered in the treated sites only after the onset of the rainy season.