Discovery of the pyridylphenylureas as novel molluscicides against the invasive snail Biomphalaria straminea, intermediate host of Schistosoma mansoni

Repurposing the drug, amprolium as a novel molluscicide against the land snail (Eobania vermiculata)

Amprolium (AMP) is an organic compound used as a poultry anticoccidiostat. The aim of this work is to repurpose AMP to control the land snail, Eobania vermiculata in the laboratory and in the field. When snails treated with ½ LC₅₀ of AMP, the levels of alkaline phosphatase (ALP), total lipids (TL), urea, creatinine, malondialdehyde (MDA), catalase (CAT), and nitric oxide (NO) were significantly increased, whereas the levels of acetylcholinesterase (AChE), total protein (TP), and glutathione (GSH) decreased. It also induced histopathological and ultrastructural changes in the digestive gland, hermaphrodite gland, kidney, mucus gland, and cerebral ganglion. Furthermore, scanning electron micrographs revealed various damages in the tegumental structures of the mantle-foot region of E. vermiculata snails. The field application demonstrated that the AMP spray caused reduced percentages in snail population of 75 and 84% after 7 and 14 days of treatment. In conclusion, because AMP disrupts the biology and physiology of the land snail, E. vermiculata, it can be used as an effective molluscicide.

Xenon-lamp simulated sunlight-induced photolysis of pyriclobenzuron in water: Kinetics, degradation pathways, and identification of photolysis products

Pyriclobenzuron 1(PBU) is a novel molluscicide developed to control Pomacea canaliculate, and little information on its environmental fate has been published. In this study, the photolysis of PBU in an aqueous environment was simulated using a xenon lamp. Results showed that the photolysis of PBU in water followed first-order kinetics, exhibiting a t0.5 of 95.1 h and 83.6 h in Milli-Q water and river water, respectively. Two main photolysis products 2(PPs) were detected by HPLC-UV and identified by UPLC-Q/TOF MS, which were formed via the hydroxylation and photocatalytic hydro-dehalogenation of PBU, respectively. The initial relative abundance of photolysis product 1 3(PP-1) in Milli-Q water was 1.55 times higher than that in river water. PP-1 was detected at 26.5 % and 76.8 % of the maximum relative abundance in the river water and Milli-Q water after 720 h, respectively. Photolysis product 2 4(PP-2) was stable in water because of its weak hydrophilicity. The PP-2 detected after 720 h in Milli-Q water and river water was 93.7 % and 93.5 % of the maximum relative abundance, respectively. Finally, ECOSAR software was used to evaluate the acute aquatic toxicity of PBU and its PPs, revealing that the PPs had lower toxicity levels to non-target aquatic organisms.

The Biosafety Evaluation for Crustaceans: A Novel Molluscicide PBQ Using against Oncomelania hupensis, the Intermediate Host of Schistosoma japonica

A new formulation (suspension concentrate, SC) of PBQ [1-(4-chlorophenyl)-3-(pyridin-3-yl) urea] was used in water network schistosomiasis-endemic areas to test its molluscicidal efficacy and the acute toxicity to crustaceans. PBQ (20% SC), 26% metaldehyde, and niclosamide suspension concentrate [MNSC (26% SC)] were used both in ditch and field experiments for the molluscicidal efficacy comparison. Acute toxicity tests of two molluscicides were conducted using Neocaridina denticulate and Eriocheir sinensis. Both in the field and ditch experiments, PBQ exhibited comparable molluscicidal efficacy with MNSC. At doses of 0.50 g/m3 and 0.50 g/m2, the snail mortalities were more than 90% three days after PBQ (20% SC) application. Compared with previous tests, PBQ (20% SC) exhibited higher molluscicidal activity than PBQ (25% wettable powder, 25% WP) used in Jiangling and showed similar mollucicidal activity to PBQ (25% WP) used in Dali and Poyang Lake. The 96 h LC50 value of MNSC against Eriocheir sinensis was 283.84 mg a.i./L. At the concentration of PBQ (20% SC) 1000 mg a.i./L, all Eriocheir sinensis were alive. The 96 h LC50 values of PBQ and MNSC against Neocaridina denticulate were 17.67 and 14.05 mg a.i./L, respectively. In conclusion, PBQ (20% SC) had a comparable molluscicidal efficacy with MNSC (26% SC) and PBQ (25% WP). Furthermore, it showed lower toxicity to the crustacean species, better solubility, no floating dust, and convenience for carriage. PBQ (20% SC) was suitable for controlling snails in the water network schistosomiasis-endemic areas.

Biomphalaria embryotoxicity test (BET): 60 years of research crossing boundaries for developing standard protocols

Snail's embryotoxicity test is a suitable approach for toxicity assay of traditional and emerging pollutants, environmental risk assessment, as well as screening and development of new molluscicides. Among the snail species, Biomphalaria spp. has been indicated as a promising model system for developing standardized test protocols for assessing the chemical toxicity using early developmental stages. Thus, the current study aimed to review the data available in the scientific literature concerning the experimental approach, type of chemicals and the response of multiple biomarkers (survival, hatching rate, development delays, morphological and behavior changes) in snail embryos applied in toxicity tests. Revised data showed that the use of Biomphalaria embryos to assess chemical toxicity began in 1962. Snail's embryotoxicity test was applied mainly for analyzing the toxicity and development of new molluscicides, while its use in ecotoxicological studies is emerging. Biomphalaria glabrata was the main species analyzed. Embryos exposed to chemicals showed bioaccumulation, mortality, hatching inhibition, development delays, and morphological malformations, which were classified into four categories (hydropic, shell, cephalic and unspecified malformations). Besides, research gaps and recommendations for future research are indicated. Overall, the results showed that the Biomphalaria embryotoxicity test (BET) is a suitable tool for toxicity and health risk assessment.

Toxicological impact of organophosphorus Chlorpyrifos 48%EC pesticide on hemocytes, biochemical disruption, and molecular changes in Biomphalaria alexandrina snails

Organophosphorus pesticides like Chlorpyrifos 48%EC were widely used to control agricultural pests. The present study aimed to evaluate the toxic effects of Chlorpyrifos 48%EC on B. alexandrina snails, the intermediate host of Schistosoma mansoni. After exposure of snails to serial concentrations to determine the LC₅₀, thirty snails for each sublethal concentration (LC₁₀ 2.1 and LC₂₅ 5.6 mg/l) in each group were exposed for 24 h followed by another 24 h for recovery. After recovery random samples were collected from hemolymph and tissue to measure the impacts on Phagocytic index, histological, biochemical, and molecular parameters. The current results showed a toxic effect of Chlorpyrifos 48%EC on adult B. alexandrina snails after 24 h of exposure at LC₅₀ 9.6 mg/l. After exposure to the sub-lethal concentrations of this pesticide, it decreased the total number of hemocytes and the percentage of small cells, while increased the percentage of hyalinocytes. The granulocyte percentage was increased after exposure to LC₁₀, while after LC₂₅, it was decreased compared to the control group. Also, the light microscopical examination showed that some granulocytes have plenty of granules, vacuoles and filopodia. Some hyalinocytes were contained shrinked nuclei, incomplete cell division and forming pseudopodia. Besides, the phagocytic index of hemocytes was significantly increased than control in all treated groups. Also, these sub-lethal concentrations increased MDA and SOD activities, while, tissue NO, GST and TAC contents were significantly decreased after exposure. Levels of Testosterone (T) and Estradiol (E) were increased significantly after exposure compared with control group. The present results showed that the concentration of DNA and RNA was highly decreased after exposure to LC₁₀, ₂₅ than the control group. Therefore, B. alexandrina snails could be used as a bio monitor of the chemical pollution. Besides, this pesticide could reduce the transmission of schistosomiasis as it altered the biological system of these snails.

Molluskicidal activity of 3-aryl-2-hydroxy-1,4-naphthoquinones against Biomphalaria glabrata

Schistosomiasis is the second most prevalent parasitic infectious disease after malaria, which affects millions of people worldwide and causes health and socioeconomic problems. The snail Biomphalaria glabrata is an intermediate host for the helminth, which is the causative agent of schistosomiasis: Schistosoma mansoni. One crucial strategy for controlling the disease is the eradication of the snail host. Niclosamide is the unique molluskicide applied in large-scale control programs, but its selectivity to other species is not adequate. Therefore, there is an urgent need to develop new molluskicides that are inexpensive, safe, and selective. Quinones are ubiquitous, playing important biological roles in fungi, plants, and others. Many synthetic molecules with relevant biological activities that contain the quinone nucleus in their structure are on the market in the therapy of cancer, malaria, or toxoplasmosis, for example. Derivatives of quinones are tools in the development of new molluskicides for Abbott laboratories. In the present work, 3-aryl-2‑hydroxy-1,4-naphthoquinones (ANs) were tested for molluskicide activity against Biomphalaria glabrata. The lethal concentration was determined for 48 h of continuous exposure. The naphthoquinones were found to have molluskicide properties. AN-15 was recorded as the highest mortality. Additionally, this analog exhibited in silico reduced ambient toxicity when compared to niclosamide. The findings of this study demonstrate that 3-aryl-2‑hydroxy-1,4-naphthoquinones are effective for the management of Biomphalaria glabrata under laboratory conditions.

Molluscicidal and cercaricidal activities of the essential oil of Dysphania ambrosioides (L.) Mosyakin & Clemants: Implications for the control of schistosomiasis

Schistosomiasis is one of the most important tropical diseases. A fundamental strategy to control its spread is the use of natural products against its vectors, which are snails of the genus Biomphalaria. The present study evaluated the chemical composition, the molluscicidal and cercaricidal effects, and the ecotoxicity of the essential oil from the aerial parts of Dysphania ambrosioides (L.) Mosyakin & Clemants (DAEO). The essential oil was obtained by hydrodistillation and analyzed by gas chromatography-mass spectrometry (GC-MS). Molluscicidal and cercaricidal activities were determined by the immersion method. Environmental toxicity was assessed from bioassays using Artemia salina larvae and Danio rerio fish. DAEO presented a 0.8% yield. The GC-MS analysis revealed the predominance of hydrocarbon monoterpenes in the oil. A total of 32 constituents was identified, with α-terpinene (50.69%) being the major compound, followed by p-cymene (13.27%) and ascaridole (10.26%). DAEO was active against adult Biomphalaria glabrata snails and demonstrated lethal effect against Schistosoma mansoni cercariae, with LC₅₀ values of 25.2 (22.7-27.8) and 62.4 (61.8-62.9) μg/mL, respectively. Regarding toxicity to non-target aquatic organisms, the oil showed LC₅₀ values of 86.9 (84.7-87.6) and 18.6 μg/mL (15.5-22.8) for A. salina and D. rerio, respectively. DAEO proved to be a promising natural product for the control of schistosomiasis, acting on both the vectors and the etiological agent of the disease. However, the use of the oil is safer in transmission sites where there are no non-target organisms, as it has showed toxicity to D. rerio fish.

Lauric acid bilayer-functionalized iron oxide nanoparticles disrupt early development of freshwater snail Biomphalaria glabrata (Say, 1818)

Iron oxide nanoparticles (IONPs) have been indicated for the control of parasites and intermediate hosts, as well as applications in several sectors of nanomedicine. However, knowledge regarding its toxicity, mechanisms of action and the role of functionalization in gastropods that act as intermediate hosts of neglected disease parasites is still scarce. The present study aimed to evaluate the toxicity of lauric acid bilayer-functionalized IONPs (LA-IONPs), lauric acid isolated (LA) and iron ions in embryos and newly-hatched Biomphalaria glabrata. The snails were exposed to different concentrations of IONPs, LA and iron ions (1.0-97.65 mg L^-1) during 144 h (embryos) and 96 h (newly-hatched) and multiple parameters were analyzed, such as mortality, hatching rate, developmental delay, and morphological changes. The results showed that both iron forms (LA-IONPs and iron ions) and LA promoted mortality, hatching inhibition and morphological changes in snail embryos in a concentration-dependent patterns. Embryos also showed iron bioaccumulation after exposure to both iron forms. High toxicity was observed in newly-hatched snails compared to embryos, indicating the protective role of ovigerous masses during the early developmental stages. LA induced high developmental toxicity compared to LA-IONPs and iron ions. Results showed the molluscicide activity of LA-IONPs and isolated LA, indicating their potential use as molluscicide in the snail control program.

Metagenome-Assembled Genomes Reveal Mechanisms of Carbohydrate and Nitrogen Metabolism of Schistosomiasis-Transmitting Vector Biomphalaria Glabrata

Biomphalaria glabrata transmits schistosomiasis mansoni which poses considerable risks to hundreds of thousands of people worldwide, and is widely used as a model organism for studies on the snail-schistosome relationship. Gut microbiota plays important roles in multiple aspects of host including development, metabolism, immunity, and even behavior; however, detailed information on the complete diversity and functional profiles of B. glabrata gut microbiota is still limited. This study is the first to reveal the gut microbiome of B. glabrata based on metagenome-assembled genome (MAG). A total of 28 gut samples spanning diet and age were sequenced and 84 individual microbial genomes with ≥ 70% completeness and ≤ 5% contamination were constructed. Bacteroidota and Proteobacteria were the dominant bacteria in the freshwater snail, unlike terrestrial organisms harboring many species of Firmicutes and Bacteroidota. The microbial consortia in B. glabrata helped in the digestion of complex polysaccharide such as starch, hemicellulose, and chitin for energy supply, and protected the snail from food poisoning and nitrate toxicity. Both microbial community and metabolism of B. glabrata were significantly altered by diet. The polysaccharide-degrading bacterium Chryseobacterium was enriched in the gut of snails fed with high-digestibility protein and high polysaccharide diet (HPHP). Notably, B. glabrata as a mobile repository can escalate biosafety issues regarding transmission of various pathogens such as Acinetobacter nosocomialis and Vibrio parahaemolyticus as well as multiple antibiotic resistance genes in the environment and to other organisms. IMPORTANCE The spread of aquatic gastropod Biomphalaria glabrata, an intermediate host of Schistosoma mansoni, exacerbates the burden of schistosomiasis disease worldwide. This study provides insights into the importance of microbiome for basic biological activities of freshwater snails, and offers a valuable microbial genome resource to fill the gap in the analysis of the snail-microbiota-parasite relationship. The results of this study clarified the reasons for the high adaptability of B. glabrata to diverse environments, and further illustrated the role of B. glabrata in accumulation of antibiotic resistance in the environment and spread of various pathogens. These findings have important implications for further exploration of the control of snail dissemination and schistosomiasis from a microbial perspective.

Myco-Synthesized Molluscicidal and Larvicidal Selenium Nanoparticles: A New Strategy to Control Biomphalaria alexandrina Snails and Larvae of Schistosoma mansoni with an In Silico Study on Induced Oxidative Stress

Schistosomiasis is a tropical disease with socioeconomic problems. The goal of this study was to determine the influence of myco-synthesized nano-selenium (SeNPs) as a molluscicide on Biomphlaria alexandrina snails, with the goal of reducing disease spread via non-toxic routes. In this study, Penicillium chrysogenum culture filtrate metabolites were used as a reductant for selenium ions to form nano-selenium. The SeNPs were characterized via UV-Vis spectrophotometer, Fourier transform infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM), dynamic light scattering (DLS), and X-ray diffraction (XRD). Myco-synthesized SeNPs had a significant molluscicidal effect on B. alexandrina snails after 96 h of exposure at a concentration of 5.96 mg/L. SeNPs also had miracidicidal and cercaricidal properties against S. mansoni. Some alterations were observed in the hemocytes of snails exposed to SeNPs, including the formation of pseudopodia and an increasing number of granules. Furthermore, lipid peroxide, nitric oxide (NO), malondialdehyde (MDA), and glutathione s-transferase (GST) increased significantly in a dose-dependent manner, while superoxide dismutase (SOD) decreased. The comet assay revealed that myco-synthesized SeNPs could cause breaks in the DNA levels. In silico study revealed that SeNPs had promising antioxidant properties. In conclusion, myco-synthesized SeNPs have the potential to be used as molluscicides and larvicides.

Control of the Invasive Agricultural Pest Pomacea canaliculata with a Novel Molluscicide: Efficacy and Safety to Nontarget Species

The golden apple snail Pomacea canaliculata is an invasive pest that causes extensive damage to agricultural production. P. canaliculata is also an intermediate host of Angiostrongylus cantonensis, which causes human eosinophilic meningitis. In this study, the molluscicidal activity and safety profile of a novel molluscicide PBQ [1-(4-chlorophenyl)-3-(pyridin-3-yl)urea] were evaluated. PBQ exhibited strong molluscicidal potency against adult and juvenile snails (LC₅₀ values of 0.39 and 0.07 mg/L, respectively). In field trials, PBQ killed 99.42% of the snails at 0.25 g a.i./m². An acute toxicity test in rats demonstrated that PBQ is a generally nonhazardous chemical. PBQ is also generally safe for nontarget organisms including Brachydanio rerio, Daphnia magna, and Apis mellifera L. Transcriptomics analysis revealed that PBQ had a significant impact on the carbohydrate and lipid metabolism pathways, which provided insights into its molluscicidal mechanism. These results suggest that PBQ could be developed as an effective and safe molluscicide for P. canaliculata control.

Comparative proteomics suggests the mode of action of a novel molluscicide against the invasive apple snail Pomacea canaliculata, intermediate host of Angiostrongylus cantonensis

Angiostrongylus cantonensis is a zoonotic parasitic nematode that is the most common cause of human eosinophilic meningitis. The invasive apple snail Pomacea canaliculata is an important intermediate host of A. cantonensis and contributes to its spread. P. canaliculata control will help prevent its invasion and transmission of A. cantonensis. The new molluscicide PBQ (1-(4-chlorophenyl)-3-(pyridin-3-yl)urea) exhibits great potency against P. canaliculata and has low toxicity against mammals and non-target aquatic organisms. We studied the mode of action of PBQ using TMT-based comparative quantitative proteomics analysis between PBQ-treated and control P. canaliculata snails. A total of 3151 proteins were identified, and 245 of these proteins were significantly differentially expressed with 135 downregulated and 110 upregulated. GO and KEGG enrichment analyses identified GO terms and KEGG pathways involved in de novo purine biosynthesis, ribosome components and translation process were significantly enriched and downregulated. The results indicated that PBQ treatment had substantial effects on the synthesis of genetic material, translation process, and protein synthesis of P. canaliculata and were likely the main cause of snail mortality.

Molecular Characterization of Rotifers and Their Potential Use in the Biological Control of Biomphalaria

Background

Schistosomiasis is one of the most important tropical parasitic diseases worldwide. Biomphalaria straminea, the intermediate host of Schistosoma mansoni, has invaded and spread to Southern China since 1974 and may pose enormous threats to public health. Controlling intermediate host snails is an effective strategy in schistosomiasis intervention. However, the only effective chemical molluscicide, niclosamide, currently recommended by WHO may cause environmental pollution, loss of biodiversity, and high costs. Thus, to counter intermediate hosts, a sustainable and environmentally friendly tool is urgently needed. Here, we conducted field investigations to collect and identify a potential snail competitor rotifer and evaluated its molluscicide effect.

Results

In this study, we collected two samples of rotifers from Shenzhen. We found both red and black phenotypic B. straminea snails at the sampling sites. We identified the rotifer population as a species of the genus Philodina according to the amplification and phylogenetic analysis results of coxI gene. We found that rotifer exposure did not significantly affect the hatching rate of B. straminea eggs but promoted the killing of juvenile snails. Meanwhile, rotifer exposure did not significantly alter the fecundity of B. straminea quantified by the number of eggs per egg mass, the number of egg masses per snail, and the number of eggs per snail; but the snails exposed to rotifers showed lower fecundity performance than the control snails. Importantly, rotifer exposure could significantly affect the development of juvenile B. straminea, showing a smaller shell diameter of the exposed snails than that of the control snails. In addition, rotifer exposure affected the life span of B. straminea snails, showing a 16.61% decline in the average life span. After rotifer exposure, the S. mansoni-infected B. straminea snails died significantly faster than those without rotifer exposure. Similar findings were observed in S. mansoni-infected Biomphalaria glabrata snails. These results implied that rotifer exposure significantly promoted the mortality of S. mansoni-infected B. straminea and B. glabrata.

Conclusions

Our study demonstrated the potential molluscicide effect of rotifers on intermediate hosts under laboratory conditions. Our findings may provide new insights into the development of biocontrol strategies for snail-borne disease transmission.

Molluscicides against the snail-intermediate host of Schistosoma: a review

Schistosomiasis, a neglected tropical disease (NTD), is one of the most prevalent parasitoses in the World. Certain freshwater snail species are the intermediate host in the life cycle of schistosome species. Controlling snails employing molluscicides is an effective, quick, and convenient intervention strategy to prevent the spread of Schistosoma species in endemic regions. Advances have been made in developing both synthetic molluscicides and molluscicides derived from plants. However, at present, the development of molluscicides is not adapted to the actual demand for snails and schistosoma controlling. We undertake a systematic review of exploitation and application of synthetic molluscicides and molluscicides derived from plants to combat intermediate host snails. The detailed molluscicidal activity, structure–activity relationship, structural feature, and possible mechanism of some molluscicides are also highlighted, which may afford an important reference for the design of new, more effective molluscicides with low environmental impact and realize the aim of controlling schistosome at transmission stages.

Essential oils as molluscicidal agents against schistosomiasis transmitting snails - a review

This review aims to describe essential oils with bioactivity on adult snails of the genera Bulinus and Biomphalaria, which are intermediate hosts of schistosomes, and brings together information relating to the importance of molluscicides and the chemical composition and toxicity of such oils for other aquatic species. Analysis of the data of original articles revealed that 50 essential oils obtained from 46 plant species were evaluated for molluscicidal activity against the genera cited. More than 80% of the volatile oils studied were active, according to the criteria of the World Health Organization (LC₉₀ or LC₁₀₀ ≤100 µg/mL or LC₅₀ <40 µg/mL), and most of the oils came from plants belonging to the Rutaceae, Lamiaceae and Pinaceae. Around 37% of the surveyed plant species were obtained in Brazil and 88% of these plants were collected in the northeast of the country, a region with a high prevalence of schistosomiasis mansoni. The essential oils with the highest toxicity against host snails had high levels of hydrocarbon monoterpenes and oxygenated monoterpenes, which may be responsible for the molluscicidal activity. Some volatile components were subjected to molluscicidal evaluation, and the monoterpene compounds exhibited a significant molluscicide effect. This review confirmed the importance of essential oils as a promising alternative for the development of natural molluscicide products. However, in order to be safe for use at sites where schistosome intermediate hosts are found, information on ecotoxicity is required and, to date, few oils have been tested against non-target aquatic species.

Toxicity of a molluscicide candidate PPU07 against Oncomelania hupensis (Gredler, 1881) and local fish in field evaluation

Schistosomiasis japonica caused by Schistosoma japonicum infection is recognized as a considerable economic and public health concern in Asia. Oncomelania hupensis is the sole intermediate host of S. japonicum. The only molluscicide recommended by World Health Organization (WHO) since 1960s is relative toxic to other aquatic species. In this article, we evaluated the novel molluscicide PPU07 in field trials on their efficiency against O. hupensis and toxicity for local fish. 25% PPU07 sulfate WP exhibited similar molluscicidal effect at 2.0 g/m² and 2.0 g/m³ in the spraying and immersion trials with the WHO recommended molluscicide niclosamide (1 g/m² and 1 g/m³). The mortality rates reached 95% and 96%, respectively. Moreover, little toxicity was observed for local fish and other aquatic organisms at the effective molluscicidal concentrations. In all, 25% PPU07 sulfate WP is a promising molluscicide for snail control, particularly in semi-commercial or commercial aquaculture ponds.