Search

• AG-Ag NPs and HG-Ag NPs were more toxic than their respective isolated extracts. • Both GP-Ag NPs treatments raised embryo mortality, with AG-Ag NPs being more toxic. • Snail embryos were more sensitive to GP-Ag NPs than newly-hatched snails. • GP-Ag NPs may be a sustainable and promising molluscicide alternative. Green silver nanoparticles (G-Ag NPs) have contributed to the development of ecological technologies with low environmental impact and safer for human health, as well as demonstrating potential for the control of vectors and intermediate hosts. However, knowledge about its toxicity in the early stages of gastropod development remains scarce. Therefore, the current study aimed to investigate the toxicity of G-Ag NPs synthesized from Croton urucurana leaf extracts in snail species Biomphalaria glabrata , which is an intermediate host for Schistosoma mansoni parasite. G-Ag NPs were synthesized using two types of plant extracts (aqueous and hydroethanolic) and characterized using multiple techniques. Bioassays focused on investigating G-Ag NPs and plant extracts were carried out with embryos and newly hatched snails, for 144 h and 96 h, respectively; toxicity was analyzed based on mortality, hatching, development inhibition, and morphological changes. Results have shown that both G-Ag NPs were more toxic to embryos and newly hatched snails than the investigated plant extracts. G-Ag NPs deriving from aqueous extract have higher molluscicidal activity than those deriving from hydroethanolic extract. Both G-Ag NPs induced mortality, hatching delay, development inhibition, and morphological changes (i.e., hydropic embryos), indicating their molluscicidal activities. Moreover, embryos were more sensitive to G-Ag NPs than newly hatched snails. Thus, the toxicity of G-Ag NPs to freshwater snails depends on the type of extracts and the snail's developmental stages. These findings can contribute to the development of green nanobiotechnologies applicable to control snails of medical importance. [Display omitted] [ABSTRACT FROM AUTHOR]

• Molecular support of S. mansoni / B. glabrata compatibility. • Non clonal snail lines with same genetic background. • 328 genes differentially regulated in resistant vs susceptible phenotypes. • Lipid compounds differed in resistant vs susceptible phenotypes. Biomphalaria glabrata is a freshwater snail and the obligatory intermediate host of Schistosoma mansoni parasite, the etiologic agent of intestinal Schistosomiasis, in South America and Caribbean. Interestingly in such host-parasite interactions, compatibility varies between populations, strains or individuals. This observed compatibility polymorphism is based on a complex molecular-matching-phenotype, the molecular bases of which have been investigated in numerous studies, notably by comparing between different strains or geographical isolates or clonal selected snail lines. Herein we propose to decipher the constitutive molecular support of this interaction in selected non-clonal resistant and susceptible snail strain originating from the same natural population from Brazil and thus having the same genetic background. Thanks to a global RNAseq transcriptomic approach on whole snail, we identified a total of 328 differentially expressed genes between resistant and susceptible phenotypes among which 129 were up-regulated and 199 down-regulated. Metabolomic studies were used to corroborate the RNAseq results. The activation of immune genes and specific metabolic pathways in resistant snails might provide them with the capacity to better respond to parasite infection. [ABSTRACT FROM AUTHOR]

• Infection rate of B. troschelii by trematoda O. felineus increased with increasing of water temperature. A possible increase in opisthorchiid infection of snails under global warming must be taken into account when planning epidemiological measures. • The autumn-winter diapause in snails life causes a "delay" in the development of intramolusken stages of opisthorchiid. Cercariae of O. felineus from B. troschelii in Western Siberia emergence only the next year after snail's infection. • Сomplete hibernation of B. troschelii In Western Siberia is observed at 10 °C. • The prevalence of O. felineus infection in B. troschelii under experimental conditions was significantly higher (30–45 %), compare with 0.19 % in natural infection survey. Opisthorchiasis is one of the most serious trematodiases in Russia, where the world's largest focus is located in the Ob basin. Temperature is an important factor affecting the metabolism of cold-blooded animals. It determines the development of the causative agent of opisthorchiasis, Opisthorchis felineus , and the success of infection of an intermediate host, the snail Bithynia troschelii. In the present study, the effect of water temperature on the development of the liver fluke O. felineus in the host snail was assessed, as was the temperature threshold at which B. troschelii hibernation initiates. Adult uninfected B. troschelii individuals collected from natural bodies of water were infected with O. felineus and maintained at different temperatures of water (18–30 °C, intervals of 3 °C) in the laboratory. Each snail was fed with embryonated uterine eggs of O. felineus at 24 °C. O. felineus infection in snails was detected using polymerase chain reaction (PCR) using specific primers. The prevalence of O. felineus infection in B. troschelii depends on the water temperature in which the snails are maintained. The highest infection rate of 45.2 % ± 12.1 % was observed at 27 °C (p ≥ 0.1). The longest lifespan of infected and uninfected B. troschelii was recorded at water temperatures of 24 and 27 °C. The snails were more successfully infected at the beginning of the warm season. Among the infected individuals, the majority (up to 85 %) were large snails. Cercarial shedding was not detected in experimentally infected snails. Apparently, this is due to the natural physiological state of Bithynia snails during the autumn–winter diapause, when opisthorchiids development in snails stops. At 10 °C, complete hibernation of all B. troschelii snails was observed, and infection by the trematodes became impossible. The highest prevalence of infection was recorded at 27 °C, suggesting that during climate warming, an increase in opisthorchiid infection of snails may occur, which must be considered when epidemiological measures are planned. [Display omitted] [ABSTRACT FROM AUTHOR]

• Ramalina aspera exhibits toxicity against B. glabrata embryos and adult snails. • Quantitative and morphological changes were observed in hemocytes of B. glabrata. • Ramalina aspera showed lethal effects against cercariae of Schistosoma mansoni. • Ramalina aspera was non-toxic to Artemia salina at low concentrations. In this study, the molluscicidal activities against Biomphalaria glabrata and cercaricidal activities against Schistosoma mansoni of the ether extract of Ramalina aspera were evaluated. Additionally, toxicity parameters were evaluated at sublethal doses in terms of the influence of the extract on the fertility and fecundity of snails, as well as morphological alterations and quantification of their immunological cells. A test with Artemia salina was also carried out, in order to verify the environmental toxicity of the compound. The ether extract of R. aspera , in which divaricatic acid was identified as the major compound, demonstrated molluscicidal activity at low concentrations against both embryos (LC 90 of 22.78, 24.23, 16.63 and 16.03 μg mL−1 for the gastrula, blastula, trochophore and veliger, respectively) and against adult snails (LC 90 of 8.66 μg mL−1), after 24 h of exposure. At the sublethal doses, it was possible to observe a decrease in fecundity and quantitative and morphological changes in the defense cells of the exposed snails. In addition, the extract of R. aspera showed a cercaricidal effect on S. mansoni from the concentration of 5.0 μg mL−1, while showing low toxicity to Artemia salina. The ether extract of R. aspera demonstrated effective molluscicidal activity on embryos and adult snails of the species B. glabrata , cercariae of S. mansoni , and presenting low toxicity on Artemia salina. In this way, it could be considered a promising compound in the development of future molluscicidal and cercaricidal agents, thus helping to combat schistosomiasis. [ABSTRACT FROM AUTHOR]

Highlights • 17 different clades of echinostomes were found in East Africa. • The majority (13/17) of clades use Biomphalaria or Bulinus as an intermediate host. • For four clades partial life cycles (2/3) were determined. Abstract Echinostomes are a diverse group of digenetic trematodes that are globally distributed. The diversity of echinostomes in Africa remains largely unknown, particularly in analyses using molecular markers. Therefore, we were interested in the composition and host usage patterns of African echinostomes, especially those that also use schistosome transmitting snails as intermediate hosts. We collected adults and larval stages of echinostomes from 19 different localities in East Africa (1 locality in Uganda and 18 in Kenya). In this study we provide locality information, host use, museum vouchers, and genetic data for two loci (28S and nad 1) from 98 samples of echinostomes from East Africa. Combining morphological features, host use information, and phylogenetic analyses we found 17 clades of echinostomes in East Africa. Four clades were found to use more than one genus of freshwater snails as their first intermediate hosts. We also determined at least partial life cycles (2 of the 3) of four clades using molecular markers. Of the 17 clades, 13 use Biomphalaria or Bulinus as a first intermediate host. The overlap in host usage creates opportunities for competition, including against human schistosomes. Thus, our study can be used as a foundation for future studies to ascertain the interactions between schistosomes and echinostomes in their respective intermediate hosts. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The prevalence of Opisthorchis viverrini infection was higher in female snails and in medium and large size snails. • In hot dry season, irrigation area aestivate snails had low mortality rate compared to non-irrigation area of previous study. • Twice rice plantation a year might provide suitable condition for snail reproduction. • Water level and shelter of rice plants during rice plantation favorite for snail living. Abstract The snail Bithynia siamensis goniomphalos acts as the first intermediate host of the human liver fluke, Opisthorchis viverrini , a major cause of cholangiocarcinoma in Northeast Thailand. In this study, we investigated host-parasite interactions in wet- and dry-season rice paddy plantation. The snails that aestivated through 4-month-dried period after rice harvest had average mortality rate of 36.45% and monthly increasing from 17.76% to 54.57%. Surprisingly, at depths greater than 5 cm experienced a higher mortality rate than upper level. Average mortality rate at the depth more than 5 cm, was 42.97%. In the initial month of aestivation, mortality rate of 0–5 and 5–10 cm depth was 9.13% and 26.39% then increase to 57.58% and 51.97%, respectively in the last 4th month. The average prevalence O. viverrini infection in snails during the study period was 0.44%. The highest prevalence of O. viverrini infection was found in the cool dry and wet season. The odds of O. viverrini infection in female snails and large snails were higher relative to male snails and medium-sized snails. The physicochemical factors involved in increased prevalence of O. viverrini infection in snail hosts were mean daily air temperature and average monthly rainfall. Short aestivation period made lower mortality in irrigation area than the previous report of non-irrigation area, that is, the aestivation is one of snail population control. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • There has been an exponential growth in the attention given to the effects of climate change on schistosomiasis in the peer-reviewed literature, but little consensus about the outcomes. • The sum of observations indicates an overall decrease in the central areas of schistosomiasis' environmental niche (tropical Africa), while an increase is expected at the cooler range margins. • A geographical bias is noted, with most studies from China, although schistosomiasis remains a much larger public health challenge currently in Africa. • Schistosoma haematobium may lose more ground in a warmer Africa compared to S. mansoni , but could gain momentum in cooler areas outside its current range. • Differences in thermal performance across parasite and snail species should be taken into account in future CC-schistosomiasis studies. Abstract The exact impact of climate change on schistosomiasis, a disease caused by a blood fluke that affects more than 250 million people mainly in tropical and subtropical countries, is currently unknown, but likely to vary with the snail-parasite species' specific ecologies and the spatio-temporal scale of investigation. Here, by means of a systematic review to identify studies reporting on impacts of climate change on the agents of schistosomiasis, we provide an updated synthesis of the current knowledge about the climate change-schistosomiasis relation. We found that, despite a recent increase in scientific studies that discuss the potential impact of climate change on schistosomiasis, only a handful of reports have applied modelling and predictive forecasting that provide a quantitative estimate of potential outcomes. The volume and type of evidence associated with climate change responses were found to be variable across geographical regions and snail-parasite taxonomic groups. Indeed, the strongest evidence stems from the People's Republic of China pertaining to Schistosoma japonicum. Some evidence is also available from eastern Africa, mainly for Schistosoma mansoni. While studies focused on the northern and southern range margins for schistosomiasis indicate an increase in transmission range as the most likely outcome, there was less agreement about the direction of outcomes from the central and eastern parts of Africa. The current lack of consensus suggests that climate change is more likely to shift than to expand the geographic ranges of schistosomiasis. A comparison between the current geographical distributions and the thermo-physiological limitations of the two main African schistosome species (Schistosoma haematobium and S. mansoni) offered additional insights, and showed that both species already exist near their thermo-physiological niche boundaries. The African species both stand to move considerably out of their "thermal comfort zone" in a future, warmer Africa, but S. haematobium in particular is likely to experience less favourable climatic temperatures. The consequences for schistosomiasis transmission will, to a large extent, depend on the parasites and snails ability to adapt or move. Based on the identified geographical trends and knowledge gaps about the climate change-schistosomiasis relation, we propose to align efforts to close the current knowledge gaps and focus on areas considered to be the most vulnerable to climate change. [ABSTRACT FROM AUTHOR]

In this review, we are discussing South Asian schistosomiasis; more specifically species which are responsible for schistosomiasis in India or South Asia – Schistosoma indicum, S. spindale, S. nasale, S. incognitum, S. gimvicum ( S.haematobium ) , Bivitellobilharzia nairi, Orientobilharzia bomfordi, O. dattai, O. turkestanicum and O.harinasutai , their survival strategies such as mild pathology to the host, producing low egg number and utilizing fresh water snails ( Indoplanorbis exustus and Lymnaea luteola ) in stagnant water bodies like ponds, lakes, ditches, low laying areas, marshy lands and rice fields. Presently, correct identification of blood fluke species, their immature stages, male schistosomes and their intermediate host details like strain variations, susceptibilities, ecologies are not well studied. Species like B. nairi, O. bomfordi, O. harinasutai ( Lymnaea rubiginosa intermediate host for O.harinasutai in Thailand) are also not well studied. Moreover, snail species like Oncomalania spp are not from South Asia, but species of Tricula or Neotricula are reported from this geography, which gives indications of S. mekongi like blood fluke presence in the area. Although in humans, cercarial dermatitis is rampant in rural population with occasional reporting of schistosome eggs in stools, human schistosomiasis is considered absent from this region, despite finding a foci (now dead) of urinary schistosomiasis in Gimvi village of Ratnagiri district, Maharashtra, India. There is great difficulty in diagnosing the infection in man and animals due to low egg production, hence development of a single step antigen detection test is the need of the hour. Interestingly, lethal effect of praziquantel was seen against S.haematobium and S.mansoni. However, this drug failed to cause significant reduction of S. incognitum and S. spindale experimentally suggesting some differences in the biology of two groups of the schistosomes. Triclabendazole showed adulticidal effect at a dose rate of 20 mg/kg body against female schistosome worms, but at lower dose (10 mg/kg body wt) of the drug, a dose that is used in treating bovine fascioliasis, it is providing chances of drug resistance of the persisting schistosomes against triclabendazole. Though the South Asian institutes have all the facilities to tackle issues related to existing schistosomes, it is recommended to develop an international collaboration by establishing an international centre on schistosomiasis in India. [ABSTRACT FROM AUTHOR]

Opisthorchis viverrini , a carcinogenic fish borne fluke, requires freshwater snails and fish as intermediate hosts. Opisthorchiasis is endemic in parts of Southeast Asia, including Central and South Vietnam. In this region the transmission by intermediate hosts has received little attention. Therefore, freshwater snails and wild fish from Bau My Tho, an opisthorchiasis endemic area in Binh Dinh Province were collected for examination of O. viverrini cercariae and metacercariae, respectively. A total of 12,000 snails belonging to six families, of which 1616 Bithynia snails representing Bithynia siamensis goniomphalos and Bithynia funiculata ; as well as 754 fish representing 12 species were examined. Shedding of O. viverrini cercariae was observed only in B. s. goniomphalos and B. funiculata , at infection rates of 0.86% and 0.14%, respectively. O. viverrini infection in Bithynia spp. was significantly associated with the habitat but not with the species and the shell size of Bithynia spp. O. viverrini metacercariae were found in 10 fish species representing both Cyprinidae and non-Cyprinidae families. The prevalence of O. viverrini infection in fish was significantly associated with species. Carassius auratus, a fish species commonly eaten raw, Rasbora aurotaenia and Puntius brevis had the highest prevalence of 74.0%, 55.8% and 31.6%, respectively. Sharing of the same snail and fish intermediate host species was found for O. viverrini and a O. viverrini duck-genotype that are sympatric in the study region. This study is the first to report on the intermediate host species of O. viverrini in Central Vietnam and indicates a high risk of acquiring opistorchiasis when eating raw fish dishes. [ABSTRACT FROM AUTHOR]

We report the genome sequence and organization of five viruses infecting snails of both Biomphalaria glabrata and Biomphalaria pfeifferi , which are vectors of the intestinal schistosomiasis. Four viruses presented a polyadenylated positive single strand RNA genome encoding one or two large open reading frames (ORFs) flanked by untranslated region. Conserved protein motifs typical of the picorna-like virus superfamily were identified in these viruses but they all presented different genome organization. Phylogenetic analysis confirmed their assignment to this superfamily. The partially characterized fifth virus presented sequence similarity for Totiviridae , a family of non-polyadenylated double-strand RNA viruses. Virus distribution and relative abundance between the five strains of Biomphalaria originating from different geographical areas was determined. Our results provide valuable information of new viruses from Biomphalaria and pave the way for future studies dedicated to their impact on snail fitness and Biomphalaria / Schistosoma interactions. [ABSTRACT FROM AUTHOR]

The freshwater snail Bulinus globosus is an important intermediate host of Schistosoma haematobium, the causative agent of urinary schistosomiasis. This disease is of major health concern, especially in Africa where the majority of cases have been reported. In this study the inter- and intra-genetic diversity and population genetic structure of B. globosus from nine locations in the KwaZulu-Natal province of South Africa was studied using four polymorphic microsatellite loci (BgZ1–BgZ4). Moderate genetic diversity was detected within populations with a mean diversity (H E ) of 0.49 ± 0.09. The majority of populations significantly deviated from Hardy-Weinberg equilibrium (p < 0.05), due to a deficit of heterozygotes. Such deviations may be due to founder events that were caused by bottlenecks that occurred as a result of frequent droughts and flooding that these snails’ habitats are exposed to. Overall, the populations studied seem to be partially inbreeders/selfers with mean estimates of 0.24/0.38. A discernable genetic structure was elucidated among populations as evident by the mean pairwise F ST of 0.58 ± 0.13. There was no significant association between genetic and geographical distance among populations, an indication of limited gene flow. This increases the chances of populations losing alleles due to genetic drift. Populations in close proximity demonstrated high genetic differentiation (58.77% total variation) due to allelic differences between them. The sample populations fell into 12 clusters, however, the populations from uMkhanyakude and uThungulu exhibited no discernable genetic structure. Genetically, the Bhobhoyi site found within the uGu district was equidistant to the two main sampling regions. [ABSTRACT FROM AUTHOR]

• B. alexandrina snails are the intermediate host of schistosomiasis mansoni. • Nerium oleander and Tecoma stans methanolic extracts have molluscicidal activities. • Both extracts exert Immunotoxical, neurotoxical and immunohistopathological disturbances of treated snails. • Nerium oleander more potent molluscicide than Tecoma stans methanolic extracts. • Both plants are cheap and ecofreindly to replace the synthetic molluscicides for snail control. Schistosomiasis is a severe illness that caused socioeconomic problems. The present study aimed to investigate the molluscicidal activities of the methanolic extract of Nerium oleander and Tecoma stans on B. alexandrina snails. The present results showed that N. oleander had the higher molluscicidal effect (LC 50 : 138.6 mg/l) than T. stans methanolic extract (LC 50 : 256.0 mg/l). These concentrations had no mortality effects on Daphnia magna during the first 12 h of the exposure, while, they had a cercaricidal activity. Exposure of B. alexandrina snails to the sub lethal concentrations (LC 10 and LC 25) of the methanolic extract of either N. oleander or T. stans caused a concentration- dependent significant decrease in their mean total number of hemocyte and hyalinocytes percent, while, both the round small and the granulocytes were increased than the control group. Exposure of B. alexandrina snails to LC 25 of the methanolic extract of N. oleander or T. stans , caused morphological alterations in the hemocytes that were studied by both light and electron microscopy. The sub lethal concentration (LC 25) significantly decreased the acetyl cholinesterase activities, acid and alkaline phosphatase levels and the protein content. Histopathological changes occurred in the digestive and the hermaphrodite glands of exposed B. alexandrina snails to LC 25 of the methanolic extracts. These alterations were confirmed by Immunohistochemistry for PCNA and Cyclin D1 expressions. Conclusively, these plants could be used to decrease the spread of schistosomiasis as they are cheap and environmentally safe to replace the synthetic molluscicides for snail control. [ABSTRACT FROM AUTHOR]

• The present study reported the prevalence of Fasciola spp. in snails from large-scale regions of China. • In China, climate and topography could affect the Fasciola spp. infection in snails. • A highly positive correlation between snails and animal infection was found in central and eastern China. • Infected snails could be an indispensable risk factor for fasciolosis transmission. Fasciolosis is a zoonotic disease as 600 million animals have been infected, and 180 million people are at risk of the infection in the world. Snail as the intermediate host of Fasciola is an essential and important factor in the transmission of fasciolosis, while its potential risk for transmission has not been studied. In this study, 3561 snails collected from large-scale regions of China were examined by nest-PCR method. A total of 345 snails were positive for Fasciola spp. , with an overall prevalence of 9.7%. Prevalence in central and southern China, characterized by a subtropical monsoon climate, was relatively low (8.0%), while a high infection rate (36.9%) was found on the plateau area (altitude > 500 m). In combination with previous findings, the study showed a highly positive correlation between snails and animal infection in central and eastern China, thus indicating that infected snails could be an indispensable risk factor for fasciolosis transmission. Epidemiological surveillance of snails will help assess the risk of fasciolosis in humans or ruminants, which promotes future prevention of this zoonotic disease. [ABSTRACT FROM AUTHOR]

• Developmental toxicity induced by lauric acid bilayer-functionalized iron oxide nanoparticles (LA-IONPs) in B. glabrata. • LA-IONPs induced toxic effects in embryos and newly-hatched snails. • Lauric acid showed greater toxicity when compared to LA-IONPs and FeCl 3. 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. [Display omitted] [ABSTRACT FROM AUTHOR]

Schistosomiasis remains of considerable public health concern in many tropical and subtropical regions of the world, including the People's Republic of China (P.R. China). The effectiveness of schistosomiasis control interventions are, among other factors, governed by the social-ecological context. However, eco-social determinants of schistosomiasis are poorly understood, particularly at the household or village levels. In the current study, residents in 26 villages of Eryuan county, Yunnan province, P.R. China, were screened for Schistosoma japonicum infection with a serological assay that was followed by stool examination for sero-positive individuals. Bayesian multilevel models with spatial random effects were employed to profile the S. japonicum infection risk based on known transmission sites of S. japonicum that are scattered across individual land parcels in this part of the country. The key risk factors identified with this approach were the absence of a sanitary stall house for livestock and presence of living and infected intermediate host snails in close proximity. We conclude that a spatially explicit Bayesian multilevel approach can deepen our understanding of eco-social determinants that govern schistosomiasis transmission at a small geographical scale. [ABSTRACT FROM AUTHOR]

Freshwater snails have received much attention for their role as intermediate hosts for trematodes causing disease in people and animals such as schistosomiasis and various food-borne trematodes. While effective medical treatment exists for some of these diseases there is need for preventive measures to reduce transmission, e.g. control of intermediate hosts because transmission patterns are often complicated due to presence of reservoir final hosts. In order to implement control measures against the intermediate host snails with minimal impact on the freshwater ecosystems and their biodiversity, a profound knowledge on transmission patterns of the trematodes is required and this is partly related to distribution, habitat preferences, and seasonal variation in density of the intermediate host species. Identification of snail species can be problematic on the basis of morphological and anatomical characters alone as some species show morphological plasticity and similarly morphological differentiation of cercariae found in snails may be difficult and this could lead to biased perceptions of intermediate host spectra and transmission patterns. In this paper, we give an overview of the snail families and their medical and veterinary importance in Asia but with main focus on Vietnam. [ABSTRACT FROM AUTHOR]

Determining of the success of a parasite's infectiveness in its snail host clearly depends on environmental conditions. Temperature, one of the most influential factors impinging on metabolism of cold-blooded animals, is believed to be an important factor in parasitic infection in snails. In order to elucidate the influence of temperature, sex and size of snails on infectivity of Opisthorchis viverrini to its first intermediate host, Bithynia siamensis goniomphalos , 960 snails were divided into 2 groups by sex. Each group was subdivided by their size into small and medium sub-groups. Each snail was fed with embryonated uterine-eggs of O. viverrini at different temperatures (16–37 °C, 3 °C intervals). Dissections were carried out 1, 7, 14, 28 and 56 days thereafter and detection of O. viverrini infection was undertaken by PCR using specific primers. Infection was strongly temperature-dependent, as temperature increases of 1 °C resulted in increased odds of infection 5.4% ( P < 0.01). A temperature of 34 °C gave the highest rate of infection of 44.14%. We also found that the odds of infection in small sized snails was 39.8% higher relative to medium sized snails ( P < 0.05). Relative to day 1, the decrease in the odds of infection was detected when the day post infection was longer ( P < 0.01). Proportion of infection in female was not different to male significantly. [ABSTRACT FROM AUTHOR]

Freshwater snails have received much attention for their role as intermediate hosts for trematodes causing disease in people and animals such as schistosomiasis and various food-borne trematodes. While effective medical treatment exists for some of these diseases there is need for preventive measures to reduce transmission, e.g. control of intermediate hosts because transmission patterns are often complicated due to presence of reservoir final hosts. In order to implement control measures against the intermediate host snails with minimal impact on the freshwater ecosystems and their biodiversity, a profound knowledge on transmission patterns of the trematodes is required and this is partly related to distribution, habitat preferences, and seasonal variation in density of the intermediate host species. Identification of snail species can be problematic on the basis of morphological and anatomical characters alone as some species show morphological plasticity and similarly morphological differentiation of cercariae found in snails may be difficult and this could lead to biased perceptions of intermediate host spectra and transmission patterns. In this paper, we give an overview of the snail families and their medical and veterinary importance in Asia but with main focus on Vietnam. [ABSTRACT FROM AUTHOR]

In order to characterize the demographic traits and spatial structure of Cameroonians Bulinus globosus, intermediate host of Schistosoma haematobium, genetic structure of seven different populations, collected from the tropical zone, was studied using six polymorphic microsatellites. Intrapopulation genetic diversity ranged from 0.37 to 0.55. Interpopulation genetic diversity variation clearly illustrated their significant isolation due to distance with gene flow substantially limited to neighbouring populations. The effective population sizes (Ne) were relatively low (from 3.0 to 18.6), which supposes a high rate from which populations would lose their genetic diversity by drift. Analysis of genetic temporal variability indicated fluctuations of allelic frequencies (35 of 42 locus-population combinations, P<0.05) characteristic of stochastic demography, and this is reinforced by events of bottlenecks detected in all populations. These findings demonstrated that Cameroonian B. globosus were mixed-maters with some populations showing clear preference for outcrossing. These data also suggest that genetic drift and gene flow are the main factors shaping the genetic structure of studied populations. [ABSTRACT FROM AUTHOR]

Highlights: [•] We measured predation by two Macrobrachium spp. prawns on medically-relevant snails in lab aquaria. [•] Prawns are voracious snail predators, consuming ca. 12% body weight daily in snails. [•] Consumption rates are predictable given prawn: snail body mass ratio. [•] Small prawns <2g cause snail population recruitment failure despite a size refuge for large snails. [•] We concluded that prawns may offer a valuable biological control option for schistosomiasis. [Copyright &y& Elsevier]

Abstract: The geographical ranges of most species, including many infectious disease agents and their vectors and intermediate hosts, are assumed to be constrained by climatic tolerances, mainly temperature. It has been suggested that global warming will cause an expansion of the areas potentially suitable for infectious disease transmission. However, the transmission of infectious diseases is governed by a myriad of ecological, economic, evolutionary and social factors. Hence, a deeper understanding of the total disease system (pathogens, vectors and hosts) and its drivers is important for predicting responses to climate change. Here, we combine a growing degree day model for Schistosoma mansoni with species distribution models for the intermediate host snail (Biomphalaria spp.) to investigate large-scale environmental determinants of the distribution of the African S. mansoni-Biomphalaria system and potential impacts of climatic changes. Snail species distribution models included several combinations of climatic and habitat-related predictors; the latter divided into “natural” and “human-impacted” habitat variables to measure anthropogenic influence. The predictive performance of the combined snail–parasite model was evaluated against a comprehensive compilation of historical S. mansoni parasitological survey records, and then examined for two climate change scenarios of increasing severity for 2080. Future projections indicate that while the potential S. mansoni transmission area expands, the snail ranges are more likely to contract and/or move into cooler areas in the south and east. Importantly, we also note that even though climate per se matters, the impact of humans on habitat play a crucial role in determining the distribution of the intermediate host snails in Africa. Thus, a future contraction in the geographical range size of the intermediate host snails caused by climatic changes does not necessarily translate into a decrease or zero-sum change in human schistosomiasis prevalence. [Copyright &y& Elsevier]

Highlights: ▶ Environmental epidemiology of schistosomiasis involves both abiotic and biotics factors. ▶ Infected Biomphalaria snails were positively associated with low wave action habitats. ▶ Parasite genotypes across infected snails had a complex spatial pattern. ▶ Fine-scale environmental epidemiology is highly spatially structured. [Copyright &y& Elsevier]

Highlights: [•] Schistosoma haematobium can be detected in infected snails before shedding. [•] Snail prepatent infection rates are higher than patent infection rates. [•] Refractory snails can be used to indicate the presence of S. haematobium miracidia. [•] Infection can be detected in refractory snails for up to 72h post penetration. [Copyright &y& Elsevier]

Highlights: ▶ We have predicted the putative secondary structures of ITS2 in Bulinus. ▶ The B. reticulatus group possesses an additional large helix (DIIa) in ITS2. ▶ We have investigated the presence of compensatory base changes in ITS2 in Bulinus. ▶ CBCs might be a new tool in the investigation of Bulinus. ▶ The taxonomic ambiguities within Bulinus remain. [Copyright &y& Elsevier]

Highlights: ▶ Use of locked nucleic acid probes to identify schistosome species groups. ▶ Development of oligochromatographic strips for schistosome species discrimination. ▶ Employment of the Schistosoma ribosomal intergenic spacer as a discriminatory tool. ▶ Comparison of methods for the detection of schistosome infection. ▶ Acc I restriction enzyme test for discriminating Schistosoma haematobium from Schistosoma bovis. [Copyright &y& Elsevier]

• Sites of human schistosome transmission are commonly invaded by aquatic plants. • Experimental plant invasions reduce algae, a key food for snails and schistosomes. • As predicted, Water hyacinth invasion suppressed snail populations. • In contrast, water lettuce invasion caused snail populations to increase. • Invasive plant traits could inform management for environment and human health. Vectors and intermediate hosts of globally impactful human parasites are sensitive to changes in the ecological communities in which they are embedded. Sites of endemic transmission of human schistosome can also be invaded by nonnative species, especially aquatic plants (macrophytes). We tested the effects on macrophyte invasions on experiment snail and schistosome populations created in 100 L mesocosm tanks. We established macrophyte-free mesocosms and those containing one of four widespread macrophyte species that are inedible to snails (duckweed, hornwort, water lettuce, or water hyacinth) and then tracked edible resources (periphyton algae) and the abundance, reproduction, and infection of snail intermediate hosts for 16 weeks. We predicted that the three floating macrophytes would reduce periphyton, thereby reducing snail reproduction, abundance, and infections. In contrast, we predicted that hornwort, which is submerged and provides substrate for periphyton growth, would increase snail reproduction and abundance. As predicted, all floating macrophytes decreased periphyton, but only water hyacinth significantly decreased snail reproduction and abundance. Snail abundance increased significantly only with water lettuce. We hypothesize that this unanticipated increase in snails occurred because water lettuce produced abundant and/or high quality detritus, subsidizing snails despite low periphyton availability. Unfortunately, we detected too few infections to analyze. Aquatic macrophytes exert strong species-specific effects on snail populations. Therefore, efforts to manage invasive plants in endemic sites should evaluate changes in resources, snails, and transmission potential. We recommend caution with management efforts that produce large amounts of detritus, which might stimulate snail populations and therefore risk of human exposure. [ABSTRACT FROM AUTHOR]

Abstract: The liver fluke Opisthorchis felineus is one of the few zoonotic trematodes that circulates in the European Union (EU). It is transmitted from freshwater snails to fish and then to fish-eating mammals, including humans, in which it causes opisthorchiasis. In the 20th century, the majority of infections in humans have been reported in Eastern Europe (e.g., Belarus, Russia, and Ukraine) and Asia (Siberia). In EU in the last fifty years, the parasite has been detected in humans of Germany and Greece, and in red foxes, polecats, cats, dogs, fish and mollusks of Germany, Italy, Poland, Portugal and Spain. In Italy, four individual cases and eight outbreaks of opisthorchiasis were reported from 2003 to 2011, for a total of 211 confirmed infections in humans. All infected persons had consumed raw fillets of tench (Tinca tinca) fished from two lakes in central Italy, but some of infected people were tourists who developed the disease in their respective home-countries. In the past decade, it has become increasingly popular to consume raw marinated fillets of fish. The objective of this review is to show how a change in human food habits have caused and increased the transmission of O. felineus, which has probably been circulating in the EU yet in a silent form for many years. [Copyright &y& Elsevier]

Abstract: Snails are the critical amplifying hosts of the liver fluke Opisthorchis viverrini, the causative agent of hepatobiliary disease and cholangiocarcinoma in the Mekong area of Southeast Asia. Bithynia funiculata, B. siamensis goniomphalos and B. s. siamensis are the first intermediate hosts of O. viverrini in Thailand. Morphological similarity between Bithynia species and subspecies creates problems for their taxonomic identification and an understanding of Bithynia systematics. In this study, multilocus enzyme electrophoresis (MEE) was applied to define genetic markers that could prove useful for investigating the systematics and population genetics of this genus in Thailand. Of the 34 enzymes examined, 20 encoding a presumptive 24 loci showed sufficient staining intensity and resolution for genetic interpretation. Of these, three loci were monomorphic and eight loci were diagnostic among the three Bithynia taxa. The remaining 13 loci were diagnostic between combinations of the three taxa. Fixed genetic differences were detected at 67–73% of loci among these taxa which in turn differed from a closely related species, Hydrobioides nassa, at 88% of loci. Seventy three percent fixed genetic differences were detected between B. funiculata and the two sub-species B. s. siamensis and B. s goniomphalos. Our data reveals similarly large genetic divergence, 67% fixed genetic differences, between B. s. siamensis and B. s. goniomphalos, which may well represent different species rather than subspecies as currently defined. The genetic markers detected will form the basis for subsequent comprehensive studies on the systematics and population genetics of Bithynia snails as well as for their role in the transmission of O. viverrini and opisthorchiasis. [Copyright &y& Elsevier]

Abstract: 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 LC50 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. [ABSTRACT FROM AUTHOR]

Abstract: Fish-borne zoonotic trematodes, such as Clonorchis sinensis, heterophyids and others, constitute a public health concern in parts of northern Vietnam and infections with these trematodes are often thought to be linked to fish culture. One common fish culture system is the integrated fish-livestock (VAC) ponds where individual households have 1 or more ponds. Fish fry, mainly of various carp species, produced in hatcheries, not necessarily local, are introduced into nursery ponds and after approximately 6 weeks, juvenile fishes are transferred to household ponds, referred to as grow-out ponds. Grow-out ponds are usually fertilized with organic debris, including animal excreta, to stimulate algal growth and subsequently fish growth. This paper describes the distribution of freshwater snails and occurrence of trematode infections in these in VAC ponds and associated habitats as part of a major study on risk factors of FZT infections in cultured fish in two communes, Nghia Lac and Nghia Phu, Nghia Hung District, Nam Dinh Province. The area is under intense rice cultivation with an extensive canal network supplying fields and also household VAC ponds. A total of 16 snail species was found and four were widely distributed i.e. Angulyagra polyzonata, Melanoides tuberculata, Bithynia fuchsiana and Pomacea insularum. Snail diversity and counts were higher in nursery ponds than in grow-out ponds. Species of the families Thiaridae and Viviparidae were more abundant than other species in VAC ponds while species of the Bithyniidae, Stenothyridae and Planorbidae dominated in rice fields and small canals. Trematode infections were found in eight snail species and among these M. tuberculata had the highest overall prevalence of infection (13.28%). No trematode infections were found in species of the Viviparidae and Ampullaridae except for metacercariae. Parapleurolophocercous and pleurolophocercous cercariae constituted the most common type of cercariae recovered, contributing 40.6% of all infections followed by echinostome cercariae (35.0%) and xiphidiocercariae (17.3%). Bithynia fuschiana and M. tuberculata had the most diverse trematode fauna. C. sinensis was not recorded in this study. The VAC pond system in this area, is very important for transmission of minute intestinal trematodes while they play little role in transmission of C. sinensis as its intermediate hosts, bithynid snails, rarely occur in these ponds. From a public health perspective this is positive as the effects of infections with intestinal trematodes are considered mild. On the other hand it is possible that even such subtle effects could have importance in public health as transmission is very intense in the area. And this in combination with the aquaculture importance, reduced marketability of fishes with high metacercariae loads, warrants that control efforts against these trematodes are initiated to reduce transmission in this production system. [Copyright &y& Elsevier]

Abstract: Schistosome transmission index can be directly used to give an overall evaluation and prediction of schistosomiasis transmission through a mathematical model. In the light of the mechanism of schistosomiasis transmission process, an improved Malone schistosome transmission index model was established based on the previous study of survivor rate of the snail under extreme temperatures by Hong Qingbiao. Meteorological data from FAO and Institute of Geographic Sciences and Resources Research, CAS was used to calculate the schistosome transmission index by the new model in the schistosomiasis epidemic region of China, and the result was re-classified into transmission index classes. The new model changed the class of “epidemic area” into that of “non-epidemic area” in the regions of the southern Henan province, the northern Anhui province and the middle Jiangsu province by transmission index threshold of 900. The geographic boundary between the epidemic and the non-epidemic regions was found fitly to coincide with the −2°C isotherm of January in China, whereas the underpinning cause needs to be further explored in the future. Finally discussed was the calculation result of this meteorological model having some difference from actual epidemiology as more factors of relevance could be considered to be incorporated into the model, also discussed were a few questions concerning the model itself and the possible future improvement directions. [Copyright &y& Elsevier]

• Some metallic nanoparticles are potent molluscicides. • Toxicity concerns necessitate the need for safer molluscicides. • Green synthesized nanoparticles could reduce environmental toxicity. 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. [ABSTRACT FROM AUTHOR]

Abstract: An investigation on the occurrence of snails in the water bodies of five selected sites i.e., Khed, Chiplun, Ratnagiri, Parchuri and Gimvi of district Ratnagiri, Maharashtra (India) was made during April–May 2006. The study revealed occurrence of nine species of snails viz., Indoplanorbis exustus, Lymnaea luteola, L. acuminata, Paludomus obesus, Ferrissia tenuis, Thiara (Melanoides) tuberculata, Bellamya bengalensis, B. dissimilis and Pila globosa, besides some species of bivalves. I. exustus was the most common species by occurrence in all the selected localities and next to it was L. luteola followed by T. tuberculata, B. bengalensis and B. dissimilis, in succession. Infection with liverfluke and amphistome cercariae was found in most of the collected snail species except P. globosa. However, the Schistosome infection has been reported only in I. exustus and L. luteola. The rice fields, streams and riverbeds shared most abundance of snails whereas those collected from rice fields shedded highest number of cercariae. [Copyright &y& Elsevier]

Abstract: As an approach to investigate the suspected involvement of cellular factors in Biomphalaria glabrata resistance/susceptibility to Echinostoma caproni, we compared protein patterns from hemocytes collected from susceptible and resistant snails. This proteomic approach revealed that twelve hemocytic proteins exhibited significant differences in their apparent abundance. The genes corresponding to five of them were characterized by a combination of mass spectrometry and molecular cloning. They encode an aldolase, an intermediate filament protein, a cytidine deaminase, the ribosomal protein P1 and the histone H4. Furthermore, we investigated their expression in parasite-exposed or -unexposed snails. These last experiments revealed changes in transcript levels corresponding to intermediate filament and histone H4 proteins post-infection. [Copyright &y& Elsevier]

Abstract: Malacological surveys carried out in the early 1970s in water bodies of the Kinshasa area, Lower Zaire (Democratic Republic of Congo), showed the appearance of a Biomphalaria species which was identified as Biomphalaria camerunensis. In 1976, other surveys confirmed the presence of the species in several sites and showed numerous infected snails with Schistosoma mansoni, demonstrating for the first time an active transmission of the parasite responsible of the intestinal schistosomiasis in this area. The most recent malacological sampling was carried out by one of us in 1994 in Mangungu River and revealed the presence of apparently the same snail species. However, conchological, anatomical and molecular studies showed that this snail may be considered as an introduced neotropical species, B. tenagophila. To our knowledge, this is the second example of the introduction of a neotropical snail host of schistosomes into Africa. [Copyright &y& Elsevier]

Twelve natural populations of Pseudosuccinea columella snails, sampled in the western and central regions of Cuba, were analyzed using the RAPD-PCR technique to screen for resistance to Fasciola hepatica. Ten OPA primers previously shown to produce marker bands for resistance and susceptibility were tested. A new population of P. columella (El Azufre, Pinar del Río) exhibited the amplification patterns of resistant snails, and its resistant status was confirmed after experimental exposure to miracidia. No genetic variability was detected across or within the susceptible isolates. Similarly, the novel resistant isolate displayed an RAPD profile identical to the profile of two other isolates previously identified as resistant to F. hepatica. However, clear differences in RAPD banding patterns and genetic distance were observed between resistant and susceptible isolates. [Copyright &y& Elsevier]

The genetic variability of Brazilian Biomphalaria glabrata populations was studied using SSR–PCR. This technique is a variant of the polymerase chain reaction (PCR), which consists of using a single primer directed towards microsatellite regions under high stringency reaction conditions. Twenty snails of each population from eight distant Brazilian localities were analyzed. Morphology and PCR–RFLP were used for previous specific identification of the snails. Bands generated after gel electrophoresis of the SSR–PCR products of each snail were used to study intra- and interpopulation genetic variability. Fifty-five prominent bands were considered in a pairwise band comparison for the determination of genetic variability. Genetic variability was greater between populations than within populations. Snail populations from the field and the laboratory presented almost no genetic differences. No relationship between genetic variability and geographic distance was found. SSR–PCR proved to be a good alternative molecular tool for the population study of B. glabrata. [Copyright &y& Elsevier]

To assess the impact of the 1998 flood on snail distribution in the lower Yangtze River Basin, two study areas were selected, one in the Poyang Lake region, and the other along the Yangtze River in Jiangsu province. Using image analysis software, geocoded Landsat TM data were used to create TNDVI maps based on the formula TNDVI=Sqrt[(band4−band3/band4+band3)+0.5]. The images taken in the flood season were classified to produce a map depicting water and land. The images taken during springtime were processed and classified based on TNDVI. Composite images were created based on the time difference analysis, combining the flood season maps and spring vegetation maps to produce a map in which potential snail habitats were identified. When compared with ground survey data collected in the spring of 2000, the correspondence rate between potential snail habitats identified by image analysis of 1998–1999 Landsat TM data and ground survey data was over 90% in both regions. Results indicate that ecology based Landsat TM image analysis provides a new way to predict snail distribution under specific environmental conditions associated with the extent of the annual flood season. [Copyright &y& Elsevier]

Objective: To study the relationship between the changes of environment and the transmission of Schistosomiasis japonica after the construction of the Three Gorge Reservoir. Methods: On the basis of the predictive data on changes of water level and sediment in the middle and lower reaches of the Yangtze River after the dam construction provided by the Yangtze River Committee on Water Conservancy, corresponding data were collected and analyzed. In order to understand the effects of changes of water level and sediment on Oncomelania hupensis, the intermediate host of Schistosoma japonicum, field surveys and ecologically intimated experiments were done. The prevalence status and factors related to transmission were investigated by epidemiology, medical geography and public health. Results: Positive impact on control of schistosomiasis is that floods in the Yangtze River will occur less and will decrease the dispersal of snails and the chances of infection for humans and animals as well. Snail habitats’ beach will be reduced in the flushed area along the Yangtze River. Exploitation of beach and elimination of snails will benefit from the beach''s uplift in flushed area. The floods ahead of time in autumn will interfere with the development of snails. Negative impact is that the flushed beaches and migratory settlements at certain altitude may become snail habitats. So the reservoir area will be a potential transmission area of schistosomiasis due to dispersal of infectious resources and Oncomelania snails. The uprising of the water body level may cause the expending of the snail habitats in some places of Jianghan plain during the transition of spring to summer. The destruction of the embankments of the Dongting Lake will be put off by its delayed flush, which causes the beach in a situation of growing reed-grass or grass for a long time that benefits the reproduction of the snails. The chances for schistosome infection to humans and animals will be on the increase, because the water regression occurs ahead of time in the Dongting Lake beach in autumn. The distribution of snails will not be affected by the changes of water level in the lower reaches of the Yangtze River after the dam is built, but the flushed section in Anhui in the recent 80 years are suitable for the snails’ development. The environmental changes due to dam construction will not obviously affect the development of snails and the transmission of schistosomiasis in the Poyang Lake area. Conclusion: The construction of the huge dam and the formation of the Three Gorge Reservoir on the Yangtze River may have both positive and negative impact on schistosomiasis transmission and control. Great effort must be made to decrease the negative impact to avoid or, at least, to decrease S. japonicum transmission. [Copyright &y& Elsevier]

• Rat lungworm infection prevalence and intensity vary among 16 snail species in Hawaii • Prevalence generally varies positively along a landscape moisture gradient • The magnitude of the prevalence response to moisture differs among species • The infection intensity response to moisture increases similarly among species • Snail capacity to transmit rat lungworm depends on the environment and host species Diverse snail species serve as intermediate hosts of the parasitic nematode Angiostrongylus cantonensis , the etiological agent of human neuroangiostrongyliasis. However, levels of A. cantonensis infection prevalence and intensity vary dramatically among these host species. Factors contributing to this variation are largely unknown. Environmental factors, such as precipitation and temperature, have been correlated with overall A. cantonensis infection levels in a locale, but the influence of environment on infection in individual snail species has not been addressed. We identified levels of A. cantonensis prevalence and intensity in 16 species of snails collected from 29 sites along an environmental gradient on the island of Oahu, Hawaii. The relationship between infection levels of individual species and their environment was evaluated using AIC model selection of Generalized Linear Mixed Models incorporating precipitation, temperature, and vegetation cover at each collection site. Our results indicate that different mechanisms drive parasite prevalence and intensity in the intermediate hosts. Overall, snails from rainy, cool, green sites had higher infection levels than snails from dry, hot sites with less green vegetation. Intensity increased at the same rate along the environmental gradient in all species, though at different levels, while the relation between prevalence and environmental variables depended on species. These results have implications for zoonotic transmission, as human infection is a function of infection in the intermediate hosts, ingestion of which is the main pathway of transmission. The probability of human infection is greater in locations with higher rainfall, lower temperature and more vegetation cover because of higher infection prevalence in the gastropod hosts, but this depends on the host species. Moreover, severity of neuroangiostrongyliasis symptoms is likely to be greater in locations with higher rainfall, lower temperature, and more vegetation because of the higher numbers of infectious larvae (infection intensity) in all infected snail species. This study highlights the variation of infection prevalence and intensity in individual gastropod species, the individualistic nature of interactions between host species and their environment, and the implications for human neuroangiostrongyliasis in different environments. [ABSTRACT FROM AUTHOR]

• Melanoides tuberculata (Thiaridae) represented a high susceptibility for parapleurolophocercous cercariae infections. • MT-ND1 gene would be first applied to specifically amplify H. taichui in the PCR reaction with high sensitivity. This study aimed to investigate the prevalence of cercarial infections in freshwater snails collected from the Chai Nat province of Central Thailand. Moreover, we aimed to develop a duplex PCR technique, using the ITS2 and candidate MT-ND1 gene, to determine the dissemination of H. taichui and H. pumilio , respectively. Six types of cercariae were discovered with an overall prevalence of 4.71% (59/1,252). The parapleurolophocercous cercariae were demonstrated to be the dominant type, infecting only Melanoides tuberculata snails. The duplex PCR was optimized for specific amplification of ITS2 for H. taichui (115 bp) and MT-ND1 for H. pumilio (335 bp). Both specific primers confirmed the specificity of the duplex PCR reaction, with no cross-reactivity with other heterophyids or related species. In addition, this duplex PCR could be used to detect co-infection at a concentration of 3.0 ng/µL. For the molecular identification, 9 of 22 parapleurolophocercous cercaria specimens in Chai Nat province generated the specific DNA fragment of H. pumilio. These results proved that the MT-ND1 gene is a species-specific method for heterophyid detection and provides a rapid method for identification based on larval and adult stages of H. taichui and H. pumilio in their intermediate and/or definitive hosts in the infected area. [ABSTRACT FROM AUTHOR]

• The first large study to determine the prevalence and genotype of T. gondii DNA in wild marine snail samples. • Surface runoff and residential water discharge were key risk factors for T.gondii in wild marine snail samples. • The first report of ToxoDB#9 genotype from wild marine snail samples in China. Increasing evidence exisits for the role that shellfish play in the epidemiology of Toxoplasma gondii in marine environment. However, limited information is available on the level of T. gondii infection in wild marine snails, which can play a role in the transmission of T. gondii to other marine organisms and humans. In this study, the prevalence of T. gondii DNA in wild marine snails collected from three coastal cities in China was determined. Between January 2018 and November 2019, 1,206 wild marine snails were randomly collected and examined for the presence of T. gondii DNA using a nested polymerase chain reaction (PCR) targeting T. gondii B1 gene. The amplified products were genotyped using multilocus PCR-restriction fragment length polymorphism analysis. We also examined whether species of snail, sampling region, sampling season, surface runoff near samplic site, residential water discharge near samplic site, and proximity to livestock farms are associated with the occurrence of T. gondii DNA in marine snails. Our results showed that 23 (1.91%) snails were positive for T. gondii B1 gene. The genotype of two of the 23 T. gondii amplicons was consistent with ToxoDB Genotype #9. Multiple logistic regression revealed that surface runoff near the sampling site (P = 0.039, odds ratio [OR] = 3.413, 95% confidence interval [CI]: 1.07-10.94) and residential water discharge near the sampling site (P = 0.021, OR = 3.990, 95%CI: 1.24-12.87) are more likely to be associated with the presence of T. gondii DNA in marine snails. The detection of T. gondii DNA in marine snails in China highlights the potential impact of the anthropogenic activities on marine organisms and the potential foodborne risk posed to humans with such an important terrestrial pathogen. [ABSTRACT FROM AUTHOR]

• Few immune related changes were found during infection. • Temptin-like protein levels were found up-regulated stimulating reproduction. • Reproductive stimulation decreases available resources for immune response. Angiostrongylus cantonensis is the main cause of human eosinophilic meningitis. Humans are accidental hosts, becoming infected due to ingestion of raw intermediate (snails and slugs) or paratenic hosts. Once ingested, the larvae migrate towards the brain where they die, causing the disease. To develop better mollusk control strategies, it is important to first understand what happens in the snail during infection, therefore our purpose was to characterize proteomic, metabolic and immunologic changes in Biomphalaria glabrata 24 h after infection with A. cantonensis. For this purpose, proteins were extracted from infected and uninfected snails and analyzed through mass spectrometry. Hemolymph was also collected, the number of hemocytes was counted and urea, nitric oxide, calcium, glycogen levels as well as alanine and aspartate aminotransferases activities were assessed. The cephalopodal region and gonad-digestive gland complex were dissected and their glycogen content was measured. After infection with A. cantonensis, we observed an increase of hemocytes and granulocytes as well as an increase in hemoglobin type 2 proteins. Temptin-like protein was also found up-regulated in infected snails. Several proteins with structural function (such as myosin heavy chain – striated muscle – like and protein LOC106059779 with ADAM/reprosolin domain) were also differentially expressed, suggesting loss/damage of internal tissues. Increase in phosphoglycerate mutase indicates an increase in glycolysis, possible to compensate the increase in energetic needs. Consequently, there is a decrease in glycogen reserves, particularly in the gonad – digestive gland complex. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The detection of Schistosoma mansoni infection in both its intermediate (snail) and definitive (human) hosts is useful in providing information on the transmission of schistosomiasis. Three pairs of previously designed PCR primers (SM1-7, SMF/R & ND5) used for the detection of S. mansoni infection were tested. We assess the utility of each of these primer sets for detecting S. mansoni infection both in artificially exposed laboratory bred Biomphalaria glabrata , and field infected African Biomphalaria sudanica and Biomphalaria pfeifferi. Two of the three primer sets (SMF/R & ND5) detected S. mansoni infection in snails, but amplification of S. mansoni DNA with SM1-7 was unreliable. For the artificially exposed laboratory bred B. glabrata snails, SMF/R and ND5 both detected infection in more snails than the cercarial shedding method. Infection detection rates were 62.4% for ND5, 57.1% for SMF/R and 50.4% using traditional cercarial shedding methods. Both SMF/R and ND5 detected S. mansoni infection in 91% of snails observed shedding cercariae, increasing to 98.5% when low stringency PCR methods were used. When comparing each of the detection methods using a Bayesian latent class analysis model, ND5 had the highest detection sensitivity and negative predictive value (NPV), while SMF/R had the highest detection specificity and positive predictive value (PPV). In field collected Biomphalaria snails, ND5 detected S. mansoni infection in 21 of 24 snails categorised as shedding S. mansoni cercariae and 4 of 24 snails categorised as shedding non -S. mansoni cercariae, while SMF/R detected infection in 18 of 24 snails categorised as shedding S. mansoni cercariae and in 3 of 24 snails categorised as shedding non -S. mansoni cercariae. All SMF/R and ND5 PCR products were shown to be S. mansoni indicating that these field snails must have been infected with both S. mansoni and cercariae from other Schistosoma species. This indicates that the two primer sets are specific for S. mansoni and will not amplify non- S. mansoni species when used at their recommended annealing temperatures. Both the SMF/R and ND5 primers effectively detected S. mansoni infection in three Biomphalaria species and have improved detection sensitivity over cercarial shedding. [ABSTRACT FROM AUTHOR]

• Taxonomy of trematodes is based on morphological traits of the adults found in vertebrates. • Molecular tools can be used for the identification of larval trematodes at family level. • ITS region of the rDNA locus is an informative marker in trematode family-level studies. • TipMT tool has successfully designed trematode family-specific ITS primers. • Multiplex PCR developed here allowed the differential identification of four trematode families present in the neotropical region. Trematodes have complex life cycles with multiple hosts. Biomphalaria snails commonly act as the first intermediate hosts of several species that can affect human and animal health. The specific identification of larval trematodes found in snails is difficult and limited, since the taxonomy of these flukes is based on morphological traits of the adults found in vertebrates. Despite recent advances worldwide, studies aiming at the use of molecular tools for the identification of cercariae found in snails are scarce in the South America. In fact, most studies are focused on Schistosoma mansoni , with few efforts directed towards the identification of larvae of other parasites found in planorbids. When reported, these other parasites are identified as cercarial types, an artificial morphological system of classification. Therefore, alternative strategies for a correct, rapid and inexpensive identification of larval trematodes found in Biomphalaria are needed. This work aimed at developing a methodology capable of distinguishing four important families of trematodes (Clinostomidae, Echinostomatidae, Schistosomatidae and Strigeidae) commonly found infecting species of Biomphalaria. Using the rDNA sequences of 34 species as input for the online tool TipMT, we designed trematode family-specific primers targeting the ITS region optimized to be used in multiplex PCR. The panel of primers identified in this study was effective at the same PCR condition. The specificity of the primers was confirmed, and the PCR sensitivity ranged from 0.1 ng to 1 ag of the DNA of the parasite. This methodology was also effective for the detection of coinfection. Through a simple, fast, accurate, and inexpensive methodology, it is possible to properly identify the trematode families included in this study in a single PCR reaction. A family level identification provides important information about probable hosts, pattern of life cycle and possible impacts that the infection generates in a specific region, thus allowing the design of better control strategies, especially for those infections that have medical and veterinary importance. [ABSTRACT FROM AUTHOR]

• Ag NPs toxicity is developmental stage dependent. • Morphological alterations in B. glabrata embryos after exposure to Ag NPs. • Ag NP toxicity to embryos and newly-born snails is concentration dependent. • Ag NPs is a potential molluscicide. 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. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• This study is the first combined omics analysis of O. hupensis infected with parasites. • 46,162 unigenes from O. hupensis were obtained and 3811 proteins were identified. • 146 and 195 differential proteins in common group and only group were respectively identified by iTRAQ-based quantitative proteomic analysis. • KEGG analysis showed that 15 and 11 differential proteins were annotated in "Infectious diseases" in the common group and the only group, respectively. Oncomelania hupensis is the obligate intermediate host of Schistosoma japonicum , and it also serves as the first intermediate host for Exorchis sp., which uses Parasilurus asoyus as its definitive host rather than humans. In previous studies, Tang et al. found that all S. japonicum larvae can be blocked and killed in O. hupensis pre-infected with Exorchis sp. eggs. However, the molecular and cellular mechanisms involved in this process remain unclear. Therefore, in the present study, a combined transcriptomic and proteomic analysis was performed to identify the differential proteins involved in the immune response to the parasite S. japonicum in the O. hupensis snail host pre-infected with Exorchis sp. trematodes. The results showed that a total of 46,162 unigenes were obtained with 23,535 (50.98%) unigenes annotated in relevant databases, and 3811 proteins from O. hupensis were identified. In addition, iTRAQ-based quantitative proteomic analysis demonstrated that among three groups (OhSj-1_vs_OhN-1, OhE-1_vs_OhN-1 and OhES-1_vs_OhN-1), there were 146 common differential proteins including 44 up-regulated proteins and 90 down-regulated proteins, and 195 differential proteins exclusive to only one experimental group, including 91 up-regulated proteins and 104 down-regulated proteins, which were defined as the Common group and the Only group, respectively. KEGG analysis showed that 15 and 11 differential proteins were annotated in "Infectious diseases" in the Common group and the Only group, respectively, indicating that these proteins may be involved in the snail host immune response to parasite infection. These data will be helpful for better understanding the host-parasite interaction, and could pave the way towards exploring the mechanisms involved in the biological control on S. japonicum in O. hupensis. They also provide valuable information about developing new anti-schistosomiasis strategies. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Previous study using the traditional method of screening snails for infection reported shedding of Schistosoma cercaria by Biomphalaria snails from a river in Nkalagu, southeastern Nigeria. This is contrary to published reports that Biomphalaria from this part of the country does not shed schistosome cercaria. Here, we employed the use of polymerase chain reaction (PCR) methods to screen and characterize the Biomphalaria snails from Nkalagu. Snails were collected from the River Uzuru in dry season, identified and subjected to molecular assays. Genomic DNA (gDNA) was extracted from whole tissues of the 212 Biomphalaria snails and amplified using conventional PCR to check for the schistosome infection level. Assay for the detection of S. mansoni infection was further done using a nested PCR (nPCR). We amplified the entire internal transcribed spacer 2 (ITS2) regions from gDNA of the 212 snails. The representative samples were sequenced and subjected to BLAST searches to confirm snail species. Of the 212 snails screened, 164 (77.4%) of the snails were infected with schistosomes, but only 16 (9.76%) of the snails were positive for S. mansoni infection. Amplification of the snails' ITS2 region yielded a product of 460 bp, and BLAST searches confirmed the snails to be B. pfeifferi , and BLAST searches confirmed the snails to be B. pfeifferi. This paper reports for the first time the presence of S. mansoni positive B. pfeifferi in Nkalagu, which suggest there may be cases of intestinal schistosomiasis in this part of Nigeria. [ABSTRACT FROM AUTHOR]

• Taxonomic classification, proposed origin and geographic spread of Oncomelania hupensis and genetic differentiation of Oncomelania hupensis quadrasi • Biology of Oncomelania hupensis quadrasi • Snail Control • Use of RS/GIS in Snail Research • Way Forward Oncomelania hupensis quadrasi is the snail intermediate host of Schistosoma japonicum in the Philippines. It was discovered by Dr. Marcos Tubangui in 1932 more than two decades after the discovery of the disease in the country in 1906. This review, the first for O. h. quadrasi , presents past and present works on the taxonomy, biology, ecology, control, possible paleogeographic origin of the snail intermediate host and future in research, control and surveillance of the snail. Extensive references are made of other subspecies of O. hupensis such as the subspecies in China for which majority of the advances has been accomplished. Contrasting views on whether the snail is to be considered an independent species of Oncomelania or as one of several subspecies of Oncomelania hupensis are presented. Snail control methods such as chemical methods using synthetic and botanical molluscicides, environmental manipulation and biological control are reviewed. Use of technologies such as Remote Sensing, Geographical Information System and landscape genetics is stressed for snail surveillance. Control and prevention efforts in the Philippines have consistently focused on mass drug administration which has proved inadequate in elimination of the disease. An integrated approach that includes snail control, environmental sanitation and health education has been proposed. Population movement such as migration for employment and economic opportunities and ecotourism and global climate change resulting in heavy rains and flooding challenge the gains of control and elimination efforts. Concern for possible migration of snails to non-endemic areas is expressed given the various changes both natural and mostly man-made favoring habitat expansion. [ABSTRACT FROM AUTHOR]

• Essential oils have molluscicidal potential against schistosome transmitting snails. • Monoterpenic compounds were predominant in essential oils with significant molluscicidal activity. • Volatile constituents have been demonstrated to be alternative chemical agents for the control of schistosome intermediate hosts. • Few oils with molluscicidal activity have been subjected to acute toxicity testing against non-target organisms. 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 (LC 90 or LC 100 ≤100 µg/mL or LC 50 <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. [ABSTRACT FROM AUTHOR]