A Contribution Toward Understanding Trematode Diversity in Freshwater Snails of the Southwestern Kathmandu Valley, Nepal

Freshwater snails act as first intermediate carriers for numerous trematodes, which can induce sickness in both humans and animals. In Manipur, various species of freshwater snails have been discovered to harbor trematode infections. In this study, we aimed to assess the prevalence of different varieties of freshwater snail species serving as the primary, intermediate hosts for various trematodes in endemic areas of paragonimiasis, a disease caused by Paragonimus trematodes found in two separate regions, Luwangsangbam matai in the Imphal East district and Moreh in the Tengnoupal district of Manipur province. These areas are known to be endemic for human paragonimiasis. We examined 4074 snails, including Bortia costula, Filopaludina bengalensis, Paludomous pustulosa,Indoplanorbis exustus using the shedding and crushing method. Our findings revealed that 43(1.05%) snails were positive for different trematode cercariae. Specifically, Bortia costula was infected with Fasciola spp, and unidentified cercariae, while Filopaludina bengalensis and Paludomous pustulosa harboured Gymnacephalous and Echinostomous cercariae. Interestingly, Indoplanorbis exustus did not show any infection with trematode cercariae. A strong association was found between these types of snail species and cercarial infection. Furthermore, statistical analysis did not demonstrate a significant correlation between the geographical location and cercarial infection among snail species. Our study provides the current status of the prevalence of trematode cercarial infection in these snails, offering insights into disease transmission dynamics and the role of snails in paragonimiasis epidemiology.

To evaluate the potential risk of transmission of angiostrongyliasis by common freshwater snails in Dali Bai Autonomous Prefecture, Yunnan Province, so as to provide insights into local surveillance of angiostrongyliasis. Common freshwater snails were collected from Dali Bai Autonomous Prefecture, Yunnan Province from March to April, 2020, and identified and bred in laboratory. SD rats were infected with third-stage larvae of Angiostrongylus cantonensis that were isolated from commercially available Pomacea canaliculata snails in Dali Bai Autonomous Prefecture, and freshwater snails were infected with the first-stage larvae of A. cantonensis that were isolated from the feces of SD rats 39 days post-infection at room temperature. The developmental process and morphological characteristics of worms in hosts were observed, and the percentages of A. cantonensis infections in different species of freshwater snails were calculated. Then, SD rats were infected with the third-stage larvae of A. cantonensis that were isolated from A. cantonensis-infected freshwater snails, and the larval development and reproduction was observed. More than 3 000 freshwater snail samples were collected from farmlands, ditches and wetlands around Erhai Lake in Dali Bai Autonomous Prefecture, and Cipangopaludina chinensis, P. canaliculata, Parafossarulus striatulus, Oncomelania hupensis robertsoni, Galba pervia, Physa acuta, Radix swinhoei, Assiminea spp., Tricula spp. and Bellamya spp. were morphologically identified. A total of 105 commercially available P. canaliculata snails were tested for A. cantonensis infections, and 2 P. canaliculata snails were found to be infected with A. cantonensis, in which the third-stage larvae of A. cantonensis were isolated. Ten species of freshwater snails were artificially infected with the third-stage larvae of A. cantonensis, and all 10 species of freshwater snails were found to be infected with A. cantonensis, with the highest positive rate of A. cantonensis infections in Bellamya spp. (62.3%, 137/204), and the lowest in C. chinensis (35.5%, 11/31). After SD rats were infected with the third-stage larvae of A. cantonensis isolated from different species of freshwater snails, mature adult worms of A. cantonensis were yielded. Multiple species of freshwater snails may serve as intermediate hosts of A. cantonensis under laboratory conditions in Dali Bai Autonomous Prefecture of Yunnan Province. Further investigations on natural infection of A. cantonensis in wild snails in Dali Bai Autonomous Prefecture seem justified.

Freshwater snails are important intermediate hosts for several parasitic diseases, including fascioliosis and schistosomiosis, with significant impacts on human and animal health. In Bangladesh, vector snails have been identified only by morphology. Here, we validate the species of freshwater snails acting as intermediate hosts for Fasciola and Schistosoma spp. using molecular and bioinformatics tools. Following morphology and morphometrics, we identified 9 species of snails: Lymnaea auricularia, Lymnaea luteola, Indoplanorbis exustus, Physa acuta, Viviparus bengalensis, Brotia spp., Thiara spp. and Pila globosa. Cercarial shedding tests revealed that L. auricularia (0.72%, 7 out of 977) and L. luteola (0.36%, 8 out of 2240) shed fasciolid cercariae, which polymerase chain reaction (PCR) confirmed. But I. exustus (5.43% 19 out of 350), L. auricularia (9.42%, 92 out of 977), L. luteola 10.09% (226 out of 2240), P. acuta (2.4%, 11 out of 450) and V. bengalensis (0.14%, 7 out of 500) shed schistosomatid cercariae. The same snail did not shed both fasciolid and schistosomatid cercariae simultaneously. PCR and sequencing of the Cox1 gene confirmed the species of the intermediate hosts. The sequences of L. auricularia, L. luteola, I. exustus,P.acuta and V. bengalensis were identical (99-99.7%) to reported sequences of these species. Phylogenetic analysis revealed that sequences of the present study for each species formed well-separated clusters with the corresponding reference sequences. Taken together, the results of this study highlight the importance of molecular tools for confirming snail species and will help target specific vector snails in the particular habitat when designing snail-borne trematode control programs.

Aim: To investigate the molluscicidal activity of aqueous extracts of Phyllanthus niruri and Euphorbia tirucalli on fresh water snails Lymnaea (Radix) acuminata and Indoplanorbis exustus (as target organisms) and on Channa punctatus fish ( as non target organism),sharing the same habitat.
 Methodology: The aqueous extracts of the stem bark and leaves of Phyllanthus niruri ( a tropical small herb, commonly known as a Bhumi Amla), belonging to the family Phyllanthaceae and the aqueous extracts of stem bark and latex of Euphorbia tirucalli (a semi-arid tropical plant, commonly called milk bush) of the family Euphorbiaceae, were investigated as plant origin molluscicides, against freshwater snails, responsible for causing fascioliasis, Lymnaea (Radix) acuminate and Indoplanorbis exustus, as well as on Channa punctatus ,using Singh and Agarwal method and POLO computer program.
 Results: A significant time and dose-dependent effect of aqueous extracts of both the plants against the freshwater snails were observed. Thus increase in exposure time, the LC50 of Phyllanthus niruri stem and leaf extracts were decreased from 267.89 mg DW/L (24h) > to 180.64mg DW/L (96h) against Lymnaea acuminata and 261.49 mg DW/L (24h)> to 136.40 mg DW/L (96h) against Indoplanorbis exustus. Likewise, the LC50 of aqueous extract of latex of Euphorbia tirucalli were decreased from 1.80 mg DW/L (24h) >to 0.65 mg DW/L (96h) against Lymnaea acuminata and 0.90 mg DW/L (24h)> to 0.28 mg DW/L (96h) against Indoplanorbis exustus, with the increase in exposure time. Its aqueous stem bark extract showed a similar pattern. These aqueous plant extracts at higher doses were also observed to be lethal to freshwater fish Channa punctatus, which share a common habitat with the freshwater snails, but the doses LC90, (24h) of snails didn’t cause any mortality to these fishes, thus indicating that these plant extracts can be safely used as molluscicides.

Because Nepal has been virtually unexplored with respect to its trematode fauna, we sampled freshwater snails from grazing swamps, lakes, rivers, swamp forests, and temporary ponds in the Chitwan district of central Nepal between July and October 2008. Altogether we screened 1,448 individuals of nine freshwater snail species (Bellamya bengalensis, Gabbia orcula, Gyraulus euphraticus, Indoplanorbis exustus, Lymnaea luteola, Melanoides tuberculata, Pila globosa, Thiara granifera and Thiara lineata) for shedding cercariae. A total of 4.3% (N=62) infected snails were found, distributed among the snail species as follows (B. bengalensis - 1, G. orcula - 11, G. euphraticus - 8, I. exustus - 39, L. luteola - 2 and T. granifera - 1). Collectively, six morphologically distinguishable types of trematode cercariae were found: amphistomes, brevifurcate-apharyngeate (likely mammalian schistosomes), clinostome, gymnocephalus (likely fasciolid), longifurcate-pharyngeate and xiphidiocercaria. I. exustus had the highest prevalence of trematode infection, and harbored all the noted cercarial types except gymnocephalus cercariae. One double infection (xiphidiocercaria and longifurcate-pharyngeate cercaria) was found in this snail. Amphistome cercariae were common in G. euphraticus, G. orcula, and I. exustus. The highest prevalence of infection (38.3%) was recorded among snails collected from temporary ponds.DOI: http://dx.doi.org/10.3126/hjs.v7i9.2183 Himalayan Journal of Sciences Vol.7 Issue 9 2011 pp.9-14

Lead (Pb) pollution in water bodies poses significant threats to aquatic biodiversity, highlighting the need for assessment through suitable bioindicators for monitoring and evaluating ecosystem health. This field study was carried out to evaluate the bioaccumulation potential of freshwater snail species in Sargodha, Pakistan. The snail species were collected between September and November, 2023, from two different types of freshwater bodies (lentic and lotic) and identified as Indoplanorbis exustus and Lymnaea acuminata. The Pb concentration was assessed in snail soft bodies and water samples through atomic absorption spectrometry. The results showcased the mean Pb concentration of 0.1572ppm (dw) in I. exustus, 0.1487ppm (dw) in L. acuminata, and 0.0344ppm (ww) in both types of water samples. There were significant differences among the water bodies, with stagnant water bodies having more Pb contamination than flowing ones. Additionally, significant differences were ascertained between the mean Pb concentration of both snail species and water samples. However, linear regression analysis showed an inverse relationship between the concentrations of Pb in water and both snail species. In addition, the bioconcentration factor (BCF) values calculated for snail species showed that both I. exustus and L. acuminata were equally good bioaccumulators of Pb in lentic and lotic water bodies. In conclusion, the study findings emphasized the urgent need for freshwater monitoring and pollution management in the region.

The effects of the herbicide atrazine on freshwater snails.

Background:Freshwater snails serve as intermediate hosts for a variety of trematodes that cause illness in the human and animal populations. Several species of freshwater snails in Thailand have been found to have larval trematode infections. We aimed to investigate a freshwater snail in Phitsanulok Province and report on its current status of larval trematode infection.Methods:Freshwater snails were collected from six localities (rice field and irrigation canal) by handpicking and using a count per unit of time sampling approach. The snails were identified by their external shell morphology. The shedding method was applied to observe the cercariae, which were photographed under a light microscope to determine their morphological types.Results:A total of 211 snails were classified into seven genera. The most abundant snail species was Lymnaea sp., representing 31.3% of the sample, followed by Physella sp., Bithynia sp., Pomacea canaliculata, Filopaludina martensi, Indoplanorbis exustus, and Melanoides tuberculata, in that order. From the sample, 21 snails (9.95%), including Bithynia sp., Lymnaea sp., I. exustus, and M. tuberculata, were infected with cercarial trematodes, which could be categorized into four types, namely amphistome, parapleurolophocercous, echinostome, and xiphidiocercaria. Amphistome emerged from Bithynia sp., and I. exustus was the most common cercaria to be recovered, representing 80.9% of all infected snails.Conclusion:This study presents the current prevalence of cercariae in infected snails within the studied area. It is important to manage intermediate host snails in order to restrict trematode life cycle completion.

The invasive apple snail Pomacea canaliculata is known as an omnivorous species, but there are only few reports of its predation. This study examined the potential of this snail as a predator of common freshwater snails in southern China. Laboratory experiments were conducted to quantify the damage of the apple snail to both early stages (eggs and/or neonates) and adults of five species of freshwater snails (Austropeplea ollula, Biomphalaria straminea, Melanoides tuberculata, Physa acuta, Sinotaia quadrata). The apple snail caused significant mortality to all of the early stages of the five snails, as well as adults of the pulmonates A. ollula, B. straminea and P. acuta, but did not consume adults of the prosobranchs M. tuberculata and S. quadrata. Such differential survival of the prey might be explained by differences in shell hardness and structure, as the adult prosobranchs were well protected by a hard shell and an operculum, whereas the pulmonates had a relatively fragile shell and lacked an operculum. The apple snail was unable to detect its prey from a distance, but it crawled quickly, which could create opportunities for direct contact with potential prey. Apple snails may therefore influence invaded ecosystems through predation on other freshwater snails.

Calotropis procera, commonly known as “Arka,” is a popular medicinal plant found throughout the tropics of Asia and Africa. It has been widely used in the Indian traditional medical system for the treatment of a variety of disease conditions due to the presence of four ursane-type triterpenoids: cardiac glycosides, alkaloids, flavonoids, tannins and saponins. This study evaluated the toxicity of aqueous, ethanolic, and chloroform extracts of different parts of plant C. procera against two species of harmful snails: Lymnaea acuminata and Indoplanorbis exustus. The toxicity of these extracts were both time- and dose-dependent. Aqueous extracts of all parts of C. procera were less toxic compared to the ethanol and chloroform extracts. The chloroform extracts of all plant parts were more toxic than aqueous and ethanol extracts. Chloroform extracts of root and latex exhibited 4.27 and 4.88 96h LC50 against Lymnaea acuminata and Indoplanorbis exustus, respectively.

The study on freshwater snails at Darbari and Kodamdesar pond was carried out for an annual cycle encompassing the years 2022-2023. The study involved diversity of snail species found in above mentioned ponds. In this study, the major focus was on the diversity of freshwater snails, i.e., different species of prosobranch and pulmonate snails found in Darbari and Kodamdesar ponds of Bikaner district. The following species Bellamya bengalensis, Digoniostoma pulchella, Indoplanorbis exustus, Lymnea acuminata were found in Darbari and Kodamdesar ponds. Among these, Bellamya bengalensis, Digoniostoma pulchella are prosobranch, while Indoplanorbis exustus, Lymnaea acuminata are pulmonate snails. Aspect of population density total prosobranch represent 50.49 no./m2 and pulmonate 31.83 no./m2. Season wise Bellamya bengalensis represent 61.48% in monsoon at Darbari pond. At Kodamdesar Indoplanorbis exustus shows 50.02% in summer season. Prosobranch have gills for water respiration and pulmonate have lungs for aerial respiration.

A survey was conducted in the lowland areas of Binh Dinh and Phu Yen provinces in south central Vietnam to study the diversity of digenean cercariae within freshwater snails. These regions are known as highly endemic areas for the transmission of liver flukes, Fasciola spp. and Opisthorchis viverrini. In total, 13 snail species were found, and 3 of these were dominant, comprising 51.9% of all collected snails, i.e., Bithynia funiculata, Melanoides tuberculata, and Radix auriculata. Cercariae were found in 5 snail species, and among these, Indoplanorbis exustus had the highest overall prevalence of infection (38.5%). No cercarial infections were found in viviparid and ampullariid snails. Morphological identification resulted in 10 cercariae types that were illustrated and measured. Among them, xiphidiocercariae and echinostomata were the most common, causing 70.55% of all cercariae infections. Bithynia species had the most diverse digenean fauna. Molecular data revealed the presence of cercariae of 13 digenean species, including O. viverrini. The 18S rDNA sequences of echinostomata and xiphidiocercariae type 3, which were shed from different snail hosts, were similar to 2 and 3 digenean species, respectively. In conclusion, our findings highlight the diversity of digenean fauna in Binh Dinh and Phu Yen provinces.

Total haemocyte counts were made in two freshwater gastropods. Lymnaea acuminata (Lamarck) f. rufescens (Gray), and Indoplanorbis exustus (Deshayes). Influence of age (shell size) was studied in groups of small, intermediate, and large-sized snails; large snails have significantly higher haemocyte counts than intermediate and small snails. Effects of changes in ambient circumstances were studied in medium-sized snails. Decreases in water temperature resulted in a rise in cell counts in both species; temperature increases gives a rise only in L. acuminata f. rufescens. Both increasing and lowering the pH of water influenced total haemocyte counts. Depending on the snail species, and on the time of exposure to altered pH levels, increases as well as decreases in cell counts were found. Replacing clean water by snail-conditioned water did not seem to influence total haemocyte counts.

Prey behavioral response to predation risk drives a range of ecological and evolutionary processes. Key to these effects is the degree to which conspecifics exhibit consistent individual differences in their response to risk or instead follow a mean population‐level pattern. Here, we employed the behavioral reaction norm framework to quantify among‐individual variation in average predator avoidance behavior (i.e., behavioral types) and the behavioral response to risk (i.e., individual plasticity) in two snail species (Helisoma trivolvis and Physa acuta) that differ in their vulnerability to predators. While both snail species exhibited substantial variation in behavioral types, individual plasticity in response to risk was remarkably invariant—both snail species increased avoidance behavior with increasing risk, but all conspecific individuals followed the population‐level pattern (i.e., parallel reaction norms). Instead, individual snails differed in how they adjusted their behavior over the course of repeated behavioral assays (n = 12 per individual), with some exhibiting increased sensitization to risk cues and others habituation. We further show that among‐individual behavioral variation, both in behavioral types and in individual responses to repeated assays, was sometimes correlated with physiological traits, providing potential mechanisms for the maintenance of this variation. In total, our results indicate that behavioral types and individual plasticity vary at different hierarchical scales (individual‐ vs. population‐level, respectively) in freshwater snails, which has implications for species interactions and the evolution of predator avoidance behavior.

Freshwater snails are widely distributed in the rice field ecosystem. Freshwater snails’ feeding and metabolic activities can potentially increase the complexity of freshwater ecosystems, particularly through the nutrient cycle. Cipangopaludina chinensis, Physa acuta, and Semisulcospira libertina are commonly found in Japan's paddy field ecosystems. Spirodela polyrhiza is expected to support biodiversity, improve soil fertility, and reduce greenhouse gas emissions in paddy field ecosystems, while providing food and shelter for the snails. In this study, we investigated the effects of these three snail species on the growth of Spirodela polyrhiza. The results showed that the presence of P. acuta or C. chinensis could promote the growth of S. polyrhiza compared with the presence of S. libertina, a mix, and the control. The relative growth rate for S. polyrhiza in the presence of P. acuta, C. chinensis + P. acuta, and C. chinesis was 1.10 ± 0.39, 1.10 ± 0.39, and 1.06 ± 0.31 fronds/day, respectively. In the S. libertina treatment, the number of S. polyrhiza fronds decreased as the snails consumed the plants. The number of fronds on the last day of treatment was 1.10 ± 1.10 fronds with a relative growth rate of 0.004 ± 0.030 fronds/day, whereas for the combination of C. chinensis + S. polyrhiza it was 4.80 ± 3.32 and 8.70 ± 3.61 fronds, respectively, with relative growth rate 0.13 ± 0.05 and 0.275 ± 0.06 fronds/day, respectively. Interestingly, these interspecific interactions increased S. polyrhiza performance, as indicated by greater frond length, root length, and frond chlorophyll content. This study highlights that interspecific interactions create complexity in the paddy field ecosystem, providing good conditions for biodiversity and indirectly supporting rice production.