Journal articles: 'Snail intermediate host'

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Eliuk, L. K., S. Brown, R. C. Wyeth, and J. T. Detwiler. "Parasite-modified behaviour in non-trophic transmission: trematode parasitism increases the attraction between snail intermediate hosts." Canadian Journal of Zoology 98, no. 7 (July 2020): 417–24. http://dx.doi.org/10.1139/cjz-2019-0251.

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Many parasites with complex life cycles cause host behavioural changes that increase the likelihood of transmission to the next host. Parasite modification is often found in trophic transmission, but its influence on non-trophic transmission is unclear. In trematodes, transmission from the first to second intermediate host is non-trophic, suggesting that free-swimming larvae (cercariae) emerging in closer proximity to the next host would have higher transmission success. We performed a series of behavioural experiments with echinostome trematodes and their snail hosts to determine if potential second hosts (ramshorn snail, genus Planorbella Haldeman, 1842) were more attracted to parasitized first hosts (marsh pondsnail, Lymnaea elodes Say, 1821). In a Y maze, a responding snail (Planorbella sp.) was placed in the base and its response to five treatments was assessed: no stimulus, turion duckweed (Lemna turionifera Landolt; a food item), non-parasitized L. elodes, parasitized L. elodes, and finally parasitized versus non-parasitized L. elodes. Snails showed some attraction to uninfected snails, but had a stronger response to infected first host snails. These results indicate that potential second host snails were more attracted to parasitized, heterospecific first host snails over non-parasitized heterospecific snails. This study demonstrates that echinostome trematodes alter snail behaviour by changing navigational choices in uninfected potential hosts through a chemical communication mechanism.

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Skorping, Arne. "Parasite–induced reduction in host survival and fecundity: the effect of the nematode Elaphostrongylus rangiferi on the snail intermediate host." Parasitology 91, no. 3 (December 1985): 555–62. http://dx.doi.org/10.1017/s003118200006279x.

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SUMMARYThe effect of the protostrongylid nematode, Elaphostrongylus rangiferi, on the fecundity and survival of an intermediate snail host, Arianta arbustorum, was studied. Over an experimental period of 12 weeks, infected snails had a significantly lower egg production than uninfected control snails. No significant difference in survival was found between infected and uninfected adult snails. Infected juvenile snails showed a consistent decrease in survival with increasing mean density of parasites. A linear relationship was found between snail instantaneous death rate over a 28–day interval and the mean number of parasites/snail. When calculated for 4–day intervals, the instantaneous death rate was highest between 8 and 12 days post–infection. It is concluded that the most pathogenic phase of this parasite is during the first moult.

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McCarthy, A. M. "The influence of second intermediate host dispersion pattern upon the transmission of cercariae of Echinoparyphium recurvatum (Digenea: Echinostomatidae)." Parasitology 101, no. 1 (August 1990): 43–47. http://dx.doi.org/10.1017/s0031182000079737.

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SUMMARYTransmission of cercariae of the echinostome digenean Echinoparyphium recurvatum was observed in experimental populations of the second intermediate host snail Lymnaea peregra. Populations of 100 snails were distributed among plastic mesh cages in an infection arena to produce different patterns of host dispersion. Cercarial transmission was investigated in host populations showing three separate patterns of host dispersion; Ideal Regular, Random and Contagious (‘Clumped’). Levels of cercarial transmission in populations showing each type of dispersion pattern were found to be significantly different. The highest rate of cercarial transmission occurred in the contagiously dispersed host population, and the lowest in the randomly dispersed population. Analysis of results from the randomly dispersed population also showed that both the mean percentage prevalence of infection, and also the mean number of cysts recovered per snail, increased significantly with the number of snails per cage. The positive relationship between the mean number of cysts per snail and the number of snails per cage was found to be best described by an exponential function. Chemosensory location of L. peregra snail hosts by E. recurvatum cercariae may provide an explanation for the patterns of cercarial transmission observed.

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Rondelaud, D., A. Novobilský, J. Höglund, M. Kašný, J. Pankrác, P. Vignoles, and G. Dreyfuss. "Growth rate of the intermediate snail host Galba truncatula influences redial development of the trematode Fascioloides magna." Journal of Helminthology 88, no. 4 (May 28, 2013): 427–33. http://dx.doi.org/10.1017/s0022149x13000370.

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AbstractA total of 850 pre-adult Galba truncatula (shell height, 4 mm), originating from four French snail populations differing in shell height at the adult stage (from 6.5 to 12 mm), were individually subjected at 20°C to single-miracidium infections with Fascioloides magna. At day 75 post-exposure, the surviving snails were dissected, and rediae and cercariae were counted. Snail groups differed in shell growth during the experiment: from 1.8 ± 0.4 mm in group A up to 4.0 ± 1.1 mm in group D. The prevalence of F. magna infection, the numbers of free rediae and cercariae significantly increased together with increasing growth of infected snails during the experiment. Group A produced 1–6 first-generation rediae per snail and the mean daughter redia production ranged from 7.5 second-generation rediae (when a single first generation per snail developed) to 2.3 (6 first-generation rediae per snail). In contrast, up to ten first-generation rediae were noted in group D, and each mother redia gave daughter rediae with averages ranging from 1.5 (ten first-generation rediae per snail) to 13 (a single first generation per snail). In conclusion, the development of F. magna in G. truncatula exhibited both inter- and intrapopulation variability, where the development of rediae and cercariae was positively correlated with snail growth.

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Ismail, Hassan A. H. A., Abed el Aziz A. el R. M. Ahmed, Young-Ha Lee, Mousab Siddig Elhag, Youngjin Kim, Seungman Cha, and Yan Jin. "Population Dynamics of Intermediate-Host Snails in the White Nile River, Sudan: A Year-Round Observational Descriptive Study." Korean Journal of Parasitology 59, no. 2 (April 22, 2021): 121–29. http://dx.doi.org/10.3347/kjp.2021.59.2.121.

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We aimed to explore the population dynamics of snail in 3 sites of the White Nile in Sudan. More specifically, we aimed to investigate the annual patterns of snail populations that act as intermediate hosts of schistosomes and monthly snail infection rates and ecological characteristics presumably related to snail populations. We collected snails for 1 year monthly at 3 different shore sites in the vicinity of El Shajara along the White Nile river in Khartoum State, Sudan. In addition, we measured air and water temperatures, water turbidities, vegetation coverages, and water depths and current speeds. Most of the collected snails were Biomphalaria pfeifferi and Bulinus truncatus. The population densities of snails and their infection rates varied across survey sites. The collected snails liberated S. mansoni and S. haematobium cercariae as well as Amphistome and Echinostome cercariae. Infected snails were found during March-June. The ecological characteristics found to be associated with the absence of snails population were: high turbidity, deep water, low vegetation coverage (near absence of vegetation), high water temperature, and high current speed. To our knowledge, this is the first longitudinal study of the snail population and ecological characteristics in the main basin of the White Nile river.

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Mohamed, A. Zakaria, Azzam Afifi, Yassir Sulieman, and Theerakamol Pengsakul. "SOME MICRO-ECOLOGICAL FACTORS INFLUENCING THE POPULATION DYNAMICS OF SCHISTOSOMIASIS INTERMEDIATE HOST SNAILS IN KHARTOUM STATE, SUDA." International Journal of Research -GRANTHAALAYAH 4, no. 8 (August 31, 2016): 147–51. http://dx.doi.org/10.29121/granthaalayah.v4.i8.2016.2573.

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This study was conducted to determine the role of some micro-ecological factors influencing the population dynamics of schistosomiasis intermediate host snails in the water bodies of Khartoum State, Sudan. The results show that the air and water temperature play a significant role in the determination of snail growth, a gradual increase of air and water temperate causing an increase in the snail population growth rate with the peak in summer. Water of high turbidity and high current speed caused a drop in the snail population. Vegetation cover in water bodies showed a significant effect on the snail population, the denser the cover the higher the snail population growth rate.

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Portet, Anaïs, Eve Toulza, Ana Lokmer, Camille Huot, David Duval, Richard Galinier, and Benjamin Gourbal. "Experimental Infection of the Biomphalaria glabrata Vector Snail by Schistosoma mansoni Parasites Drives Snail Microbiota Dysbiosis." Microorganisms 9, no. 5 (May 18, 2021): 1084. http://dx.doi.org/10.3390/microorganisms9051084.

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Host-parasite interaction can result in a strong alteration of the host-associated microbiota. This dysbiosis can affect the fitness of the host; can modify pathogen interaction and the outcome of diseases. Biomphalaria glabrata is the snail intermediate host of the trematode Schistosoma mansoni, the agent of human schistosomiasis, causing hundreds of thousands of deaths every year. Here, we present the first study of the snail bacterial microbiota in response to Schistosoma infection. We examined the interplay between B. glabrata, S. mansoni and host microbiota. Snails were infected and the microbiota composition was analysed by 16S rDNA amplicon sequencing approach. We demonstrated that the microbial composition of water did not affect the microbiota composition. Then, we characterised the Biomphalaria bacterial microbiota at the individual scale in both naive and infected snails. Sympatric and allopatric strains of parasites were used for infections and re-infections to analyse the modification or dysbiosis of snail microbiota in different host-parasite co-evolutionary contexts. Concomitantly, using RNAseq, we investigated the link between bacterial microbiota dysbiosis and snail anti-microbial peptide immune response. This work paves the way for a better understanding of snail/schistosome interaction and should have critical consequences in terms of snail control strategies for fighting schistosomiasis disease in the field.

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Allan, F., D. Rollinson, J. E. Smith, and A. M. Dunn. "Host choice and penetration bySchistosoma haematobiummiracidia." Journal of Helminthology 83, no. 1 (March 2009): 33–38. http://dx.doi.org/10.1017/s0022149x08073628.

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AbstractSchistosome parasites commonly show specificity to their intermediate mollusc hosts and the degree of specificity can vary between parasite strains and geographical location. Here the role of miracidial behaviour in host specificity ofSchistosoma haematobiumon the islands of Zanzibar is investigated. In choice-chamber experiments,S. haematobiummiracidia moved towardsBulinus globosussnail hosts in preference to empty chambers. In addition, miracidia preferred uninfected over patentB. globosus. This preference should benefit the parasite as patent snails are likely to have mounted an immune response toS. haematobiumas well as providing poorer resources than uninfected snails. Miracidia also discriminated between the hostB. globosusand the sympatric, non-host speciesCleopatra ferruginea. In contrast,S. haematobiumdid not discriminate against the allopatricBulinus nasutus. Penetration of the host by miracidia was investigated by screening snails 24 h after exposure using polymerase chain reaction (PCR) withS. haematobiumspecificDraI repeat primers. There was no difference in the frequency of penetration ofB. globosusversusB. nasutus. These responses to different snail species may reflect selection pressure to avoid sympatric non-hosts which represent a transmission dead end. The distribution ofB. nasutuson Unguja is outside the endemic zone and so there is less chance of exposure toS. haematobium, hence there will be little selection pressure to avoid this non-host snail.

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KOCK, S. "Investigations of intermediate host specificity help to elucidate the taxonomic status of Trichobilharzia ocellata (Digenea: Schistosomatidae)." Parasitology 123, no. 1 (July 2001): 67–70. http://dx.doi.org/10.1017/s0031182001008101.

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The avian schistosomatid Trichobilharzia ocellata plays an important role as causative agent of cercarial dermatitis of humans in Europe. In order to improve the taxonomic knowledge on this parasite, studies of miracidial chemo-orientation as well as experimental infections of different snail species were conducted using strains of T. ocellata and T. franki. Both schistosomes exhibited a high intermediate host specificity. The miracidia clearly preferred the SCW (snail-conditioned water) of the respective natural intermediate host to SCW of other sympatric snail species. T. ocellata proved to be capable of infecting Lymnaea stagnalis and Stagnicola palustris, but could not develop in Radix ovata or R. auricularia. T. franki established an infection in specimens of R. auricularia and R. ovata, but not in L. stagnalis or S. palustris. The results imply that the intermediate host spectrum of T. ocellata is limited to L. stagnalis and S. palustris. Findings of T. ocellata (or Cercaria ocellata) that originated from snails of the genus Radix are likely to have actually belonged to species such as T. franki or T. regenti. The assumption that T. szidati is synonymous to T. ocellata is also discussed.

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KALBE, M., B. HABERL, J. HERTEL, and W. HAAS. "Heredity of specific host-finding behaviour in Schistosoma mansoni miracidia." Parasitology 128, no. 6 (May 13, 2004): 635–43. http://dx.doi.org/10.1017/s0031182004005037.

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Two strains of Schistosoma mansoni were used to investigate the hereditary basis of species-specific host recognition by analysing behavioural responses of miracidia to snail-conditioned water. An Egyptian strain of S. mansoni, capable of distinguishing its host snail Biomphalaria alexandrina from other snails was cycled repeatedly through Biomphalaria glabrata, the intermediate host of a Brazilian strain known to respond even to non-susceptible snails with high intensity. After 5 cycles in the non-natural host, miracidia of the Egyptian strain still retained their preference for the original host snail. In a second experiment, host-finding behaviour of hybrids between these two parasite strains was studied. In the F1 generation, hybrids of both parental combinations showed the same low degree of specificity as the pure-bred Brazilian strain. Approximately one quarter of F2 hybrids proved to be as discriminatory as the Egyptian strain, confirming dominant Mendelian inheritance of non-specificity in schistosome miracidial host-finding behaviour. Moreover, hybrids seem to have lost the ability to develop in B. alexandrina, possibly suggesting a link between host recognition and host compatibility. The heredity of this behavioural trait is of evolutionary and epidemiological significance, since a shift to low host-finding specificity might have been a prerequisite for S. mansoni to acquire new host snails after being introduced to South America by the slave trade.

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Haas, W., M. Körner, E. Hutterer, M. Wegner, and B. Haberl. "Finding and recognition of the snail intermediate hosts by 3 species of echinostome cercariae." Parasitology 110, no. 2 (February 1995): 133–42. http://dx.doi.org/10.1017/s0031182000063897.

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SUMMARYFinding and recognition of snail second intermediate hosts was studied in cercariae of 3 echinostome species. The cercariae of the 3 species accumulated in snail-conditioned water (SCW) with 2 types of orientation mechanisms and responded to different small molecular weight (< 500 Da) components of SCW. Pseudechinoparyphium echinatum and Echinostoma revolutum cercariae returned by swimming an arc, when swimming in decreasing concentration gradients of SCW (turnback swimming). The stimulating cues of SCW were identified as hydrophilic organic molecules, probably posessing amino groups. Amino acids contributed to the attractivity of SCW, at least in P. echinatum, but they could not account for the complete attractivity of SCW. Hypoderaeum conoideum were directed chemotactically and swam along increasing concentration gradients of small peptides within SCW, but in decreasing SCW gradients they showed no turn-back swimming. Chemotactic orientation in H. conoideum only started 1 h after emission, which may assist the cercariae to leave the immediate area of their first intermediate host snails and to disperse. Attachments occurred specifically to snail hosts in the 3 species and were stimulated by macromolecular mucus compounds, probably mainly by viscoelastic properties of the mucus. The results of this study show, that host-finding mechanisms and the stimulating host cues of snail invading echinostome cercariae differ considerably from those of schistosome miracidia.

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ONDRAČKOVÁ, M., A. šIMKOVÁ, M. GELNAR, and P. JURAJDA. "Posthodiplostomum cuticola(Digenea: Diplostomatidae) in intermediate fish hosts: factors contributing to the parasite infection and prey selection by the definitive bird host." Parasitology 129, no. 6 (November 18, 2004): 761–70. http://dx.doi.org/10.1017/s0031182004006456.

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Infection parameters ofPosthodiplostomum cuticola, a digenean parasite with a complex life-cycle, were investigated in fish (the second intermediate host) from 6 floodplain water bodies over 2 years. A broad range of factors related to abiotic characteristics of localities, density of the first intermediate (planorbid snails) and definitive (wading birds) hosts and fish community structure were tested for their effects onP. cuticolainfection in juvenile and adult fish. Characters of the littoral zone and flood duration were found to be important factors for the presence of the first intermediate and definitive hosts. Visitation time of definitive bird hosts was also related to adult fish host density. Localities withP. cuticolainfected fish were visited by a higher number of bird species. Infection ofP. cuticolain fish and similarities in infection among fish host assemblages were correlated with fish host density and fish species composition. Parasite infection in both adult and juvenile fishes was associated with the slope of the bank and the bottom type, in particular in juvenile fish assemblages with snail host density. We conclude that habitat characteristics, snail host density and fish community structure contribute significantly toP. cuticolainfection in fish hosts.

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Zhytova, O. "Cercaria of the Trematode Plagiorchis Mutationis (Trematoda, Plagiorchiidae) from the Pond Snails, Lymnaea Stagnalis, in Ukraine." Vestnik Zoologii 44, no. 4 (January 1, 2010): e-29-e-32. http://dx.doi.org/10.2478/v10058-010-0022-x.

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Cercaria of the Trematode Plagiorchis Mutationis (Trematoda, Plagiorchiidae) from the Pond Snails, Lymnaea Stagnalis, in Ukraine Morphological characteristics and measurements of Plagiorchis mutationis Panova, 1927 cercaria found for the first time in the intermediate host, pond snail Lymnaea stagnalis in Ukraine are given.

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Muñoz-Antolí, C., R. Toledo, and J. G. Esteban. "The life cycle and transmission dynamics of the larval stages ofHypoderaeum conoideum." Journal of Helminthology 74, no. 2 (June 2000): 165–72. http://dx.doi.org/10.1017/s0022149x00000238.

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AbstractThe morphology of the different larval stages and life cycle ofHypoderaeum conoideum(Trematoda: Echinostomatidae) are described. The freshwater snail speciesLymnaea peregra(Gastropoda: Lymnaeidae) serves as the natural first intermediate host and this andL. corvusserve as experimental first intermediate hosts. These and other freshwater snails, such asPhysella acutaandGyraulus chinensis, in turn serve as second intermediate hosts. Adult worms were obtained from chicks and ducks, but not from rats, mice and golden hamsters. The morphology of the larval stages is compared with previous work onH. conoideum. Several aspects of the biology of the life history stages are described with emphasis on the transmission dynamics of the free-living stages. Differential suitability of the snail species that may act as first and/or second intermediate hosts is studied and discussed.

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Calata, Fritz Ivy C., Camille Z. Caranguian, Jillian Ela M. Mendoza, Raffy Jay C. Fornillos, Ian Kim B. Tabios, Ian Kendrich C. Fontanilla, Lydia R. Leonardo, et al. "Analysis of Environmental DNA and Edaphic Factors for the Detection of the Snail Intermediate Host Oncomelania hupensis quadrasi." Pathogens 8, no. 4 (September 23, 2019): 160. http://dx.doi.org/10.3390/pathogens8040160.

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Background: The perpetuation of schistosomiasis japonica in the Philippines depends to a major extent on the persistence of its intermediate host Oncomelania hupensis quadrasi, an amphibious snail. While the malacological survey remains the method of choice in determining the contamination of the environment as evidenced by snails infected with schistosome larval stages, an emerging technology known as environmental DNA (eDNA) detection provides an alternative method. Previous reports showed that O. hupensis quadrasi eDNA could be detected in water, but no reports have been made on its detection in soil. Methods: This study, thus focused on the detection of O. hupensis quadrasi eDNA from soil samples collected from two selected schistosomiasis-endemic barangays in Gonzaga, Cagayan Valley using conventional and TaqMan-quantitative (qPCR) PCRs. Results: The results show that qPCR could better detect O. hupensis quadrasi eDNA in soil than the conventional method. In determining the possible distribution range of the snail, basic edaphic factors were measured and correlated with the presence of eDNA. The eDNA detection probability increases as the pH, phosphorous, zinc, copper, and potassium content increases, possibly indicating the conditions in the environment that favor the presence of the snails. A map was generated to show the probable extent of the distribution of the snails away from the body of the freshwater. Conclusion: The information generated from this study could be used to determine snail habitats that could be possible hotspots of transmission and should, therefore, be targeted for snail control or be fenced off from human and animal contact or from the contamination of feces by being a dumping site for domestic wastes.

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Jones, Rhys Aled, Chelsea N. Davis, Dewi Llyr Jones, Fiona Tyson, Emma Davies, David Cutress, Peter M. Brophy, Michael T. Rose, Manod Williams, and Hefin Wyn Williams. "Temporal dynamics of trematode intermediate snail host environmental DNA in small water body habitats." Parasitology 148, no. 12 (June 30, 2021): 1490–96. http://dx.doi.org/10.1017/s0031182021001104.

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AbstractEnvironmental DNA (eDNA) surveying has potential to become a powerful tool for sustainable parasite control. As trematode parasites require an intermediate snail host that is often aquatic or amphibious to fulfil their lifecycle, water-based eDNA analyses can be used to screen habitats for the presence of snail hosts and identify trematode infection risk areas. The aim of this study was to identify climatic and environmental factors associated with the detection of Galba truncatula eDNA. Fourteen potential G. truncatula habitats on two farms were surveyed over a 9-month period, with eDNA detected using a filter capture, extraction and PCR protocol with data analysed using a generalized estimation equation. The probability of detecting G. truncatula eDNA increased in habitats where snails were visually detected, as temperature increased, and as water pH decreased (P < 0.05). Rainfall was positively associated with eDNA detection in watercourse habitats on farm A, but negatively associated with eDNA detection in watercourse habitats on farm B (P < 0.001), which may be explained by differences in watercourse gradient. This study is the first to identify factors associated with trematode intermediate snail host eDNA detection. These factors should be considered in standardized protocols to evaluate the results of future eDNA surveys.

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Jones, Isabel J., Susanne H. Sokolow, Andrew J. Chamberlin, Andrea J. Lund, Nicolas Jouanard, Lydie Bandagny, Raphaël Ndione, et al. "Schistosome infection in Senegal is associated with different spatial extents of risk and ecological drivers for Schistosoma haematobium and S. mansoni." PLOS Neglected Tropical Diseases 15, no. 9 (September 27, 2021): e0009712. http://dx.doi.org/10.1371/journal.pntd.0009712.

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Schistosome parasites infect more than 200 million people annually, mostly in sub-Saharan Africa, where people may be co-infected with more than one species of the parasite. Infection risk for any single species is determined, in part, by the distribution of its obligate intermediate host snail. As the World Health Organization reprioritizes snail control to reduce the global burden of schistosomiasis, there is renewed importance in knowing when and where to target those efforts, which could vary by schistosome species. This study estimates factors associated with schistosomiasis risk in 16 villages located in the Senegal River Basin, a region hyperendemic for Schistosoma haematobium and S. mansoni. We first analyzed the spatial distributions of the two schistosomes’ intermediate host snails (Bulinus spp. and Biomphalaria pfeifferi, respectively) at village water access sites. Then, we separately evaluated the relationships between human S. haematobium and S. mansoni infections and (i) the area of remotely-sensed snail habitat across spatial extents ranging from 1 to 120 m from shorelines, and (ii) water access site size and shape characteristics. We compared the influence of snail habitat across spatial extents because, while snail sampling is traditionally done near shorelines, we hypothesized that snails further from shore also contribute to infection risk. We found that, controlling for demographic variables, human risk for S. haematobium infection was positively correlated with snail habitat when snail habitat was measured over a much greater radius from shore (45 m to 120 m) than usual. S. haematobium risk was also associated with large, open water access sites. However, S. mansoni infection risk was associated with small, sheltered water access sites, and was not positively correlated with snail habitat at any spatial sampling radius. Our findings highlight the need to consider different ecological and environmental factors driving the transmission of each schistosome species in co-endemic landscapes.

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ESCH, G. W., L. A. CURTIS, and M. A. BARGER. "A perspective on the ecology of trematode communities in snails." Parasitology 123, no. 7 (November 2001): 57–75. http://dx.doi.org/10.1017/s0031182001007697.

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This paper presents a perspective on the ecology of trematodes in snail hosts based on recent evidence. Because flukes use snails almost obligatorily as first intermediate hosts, we highlight the role of gastropods as keystone species for trematodes and their communities. After reviewing recent developments in the transmission of trematodes to and from snails, we discuss trematode communities within individual snails (infracommunities) and in snail populations (component communities). Results garnered using various protocols at the infracommunity level are reviewed. The few data available, all from marine systems, indicate that low colonization rates characterize infracommunities, suggesting that trematode infracommunities tend to be isolationist in character rather than interactive. The variety of trematode species present in a component community seems to be determined by spatial overlap of definitive hosts. Relative abundance of species in a component community shows little dependence on negative interspecific interactions at the level of the infracommunity. Temporal aspects of trematode communities are related to the life history of the host snail. The component communities of long-lived snails (mostly marine) integrate many infection episodes whereas shorter-lived snails (mostly freshwater) acquire new component communities each time host cohorts turnover.

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Żbikowska, Elżbieta. "One snail – three Digenea species, different strategies in host-parasite interaction." Animal Biology 61, no. 1 (2011): 1–19. http://dx.doi.org/10.1163/157075511x554383.

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AbstractThe mostly lab-based studies on snail-trematode interactions should be complemented by research on naturally invaded hosts. In this mini-review, three different ways of snail exploitation by Digenea larvae are presented. Morphological, physiological and behavioral changes caused by three parasites in the same naturally infected host – Lymnaea stagnalis – differ in species-dependent fashion. The impact of a snail-trematode interaction depends on parasite virulence (i.e. parasite induced lost of fitness of the host). The pathogenicity varies with the survival strategy of the invader. Sporocyst-born Plagiorchis elegans, which uses the same Lymnaea stagnalis individual as a first but also as a second intermediate host, does not disturb host processes as strongly as redia-born Echinoparyphium aconiatum. The third parasite species – Diplostomum pseudospathaceum, also sporocyst-born – is more virulent than P. elegans, but it can modify and relax host exploitation to overwinter in the snail. The data presented demonstrate that successful use of first intermediate host can be arranged in different ways.

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Woolhouse, M. E. J. "On the interpretation of age—prevalence curves for schistosome infections of host snails." Parasitology 99, no. 1 (August 1989): 47–56. http://dx.doi.org/10.1017/s0031182000061011.

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SUMMARYThe prevalence of schistosome infections in intermediate host snails varies with snail age. The relationship between age and prevalence, the age—prevalence curve, is complex and may vary in space and time, and among parasite—host species. Field studies show that the shape of the age—prevalence curve may be seasonally variable, and that at some times there may be a decline in prevalence among older snails. This paper attempts to explain these observations in terms of the underlying epidemiological processes. A discrete-time version of Muench's catalytic model for age-dependent infection is developed. Model simulations were carried out using life-history and epidemiological parameters derived from studies ofSchistosoma haematobium—Bulinus globususin Zimbabwe. Analysis of model behaviour identifies aspects of the schistosome— snail interaction that affect the shape of the age—prevalence curve. The following features can result in a decline in prevalence among older snails. (1) A decrease in the survival rate of patent infected snails with age. (2) A decrease in the force of infection with age. (3) A high rate of loss of infection. (4) A heterogeneity in the snail population such that the probability of infection is correlated with snail fecundity. (This would occur if there existed a spatial correlation between force of infection and fecundity, or if there were a correlation between fecundity and susceptibility.) The evidence for the occurrence of these features in the field is assessed. Survival rate is related more closely to the duration of patent infection than to ageper se. The evidence for age-dependent force of infection is equivocal. Significant loss-of-infection rates have yet to be demonstrated. Heterogeneities in force of infection and fecundity have been reported and, for the Zimbabwe data, this mechanism can explain seasonally in the age—prevalence curve as a function of known seasonal variation in the force of infection and snail fecundity.

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Hairani, Budi, Syarif Hidayat, and Paisal Paisal. "KONFIRMASI KEBERADAAN Fasciola gigantica DAN HOSPES PERANTARA DI LINGKUNGAN PEMUKIMAN EKOSISTEM RAWA KABUPATEN HULU SUNGAI UTARA, KALIMANTAN SELATAN." Vektora : Jurnal Vektor dan Reservoir Penyakit 10, no. 1 (June 30, 2018): 75–82. http://dx.doi.org/10.22435/vk.v10i1.1054.

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Fasciola Gigantica infection occurs in swamp buffalo on livestock in the swamp area of Hulu Sungai Utara District. Geographically, the livestock area is linked to the villages of Sungai Papuyu and Kalumpang Dalam by swamp water with no barrier. Such condition allows the snail as intermediate host of F. gigantica in livestock areas easily spread to residential areas and, therefore, raises the risk of transmission to humans. This study aimed to confirm the presence of F. gigantica in the cercariae form and snails in the area around the settlement of both villages. The study was an observational study of cross-sectional design, conducted in August-December 2014 . Snail sampling was conducted at the Sungai Papuyu and Kalumpang Dalam village using hand collection method. To find cercariae in the snail crushing technique was performed. Cercariae was confirmed by means of PCR to ensure they are F. gigantica in the Laboratory of Molecular Biology, Lambung Mangkurat University, Banjarbaru. The results in both villages showed 6 genera of snail, namely Pomacea, Bellamyâ , Indoplanorbis , Lymnaea , Gyraulus and Melanoides . There are 3 types of cercariae in the snails, namely Echinostome cercariae , Brevifurcate – pharyngeate cercariae and Sulcatomicrocercous cercariae. PCR shows positive samples of F. gigantica in the Echinostome cercariae form in Lymnaea and Indoplanorbis snails. This confirms the presence of F. gigantica cercariae around the settlements area and Lymnaea and Indoplanorbis snail are the first intermediate hosts.

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Ménard, L., and M. E. Scott. "Seasonal occurrence of Cyathocotyle bushiensis Khan, 1962 (Digenea: Cyathocotylidae) metacercariae in the intermediate host Bithynia tentaculata L. (Gastropoda: Prosobranchia)." Canadian Journal of Zoology 65, no. 12 (December 1, 1987): 2980–92. http://dx.doi.org/10.1139/z87-452.

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Cyathocotyle bushiensis Khan, 1962 (Digenea) has been associated with late-summer duck mortality in southern Quebec. In an attempt to relate these die-offs with seasonal availability of the infective metacercariae to the ducks, two intermediate host (Bithynia tentaculata L.) populations were regularly sampled in 1984 and 1985. Prevalence varied between 5.3 and 57.3% at the South River, and between 9.1 and 49.7% at Lake St. Francis over the period of the study. Maximum abundances at the two localities were 1.38 and 1.66 metacercariae per snail, respectively. No close link between availability of metacercariae and periods of duck mortality was found, as the total prevalence and abundance of the cysts decreased through the summer, probably as a consequence of snail recruitment and low cercarial transmission rates, and increased in the autumn. Prevalence and abundance of metacercariae increased with snail age, estimated by both size and annual growth lines, and the metacercariae were found to be aggregated in the snail population. Comparison of infection levels reached at the end of the two sampling seasons by two year classes of B. tentaculata suggested that transmission of cercariae was higher in 1984 than in 1985. This was supported by the results of exposure of sentinel snails in an infected area during the 2 years of the study: transmission was detected in 1984 but not in 1985. In addition to C. bushiensis metacercariae, the sentinel snails acquired Sphaeridiotrema globulus (Rudolphi, 1814), another potential duck pathogen, in both years. The peak rate of transmission of S. globulus metacercariae occurred in August.

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Michelson, Edward H. "The intermediate snail-host: an agenda for future study." Memórias do Instituto Oswaldo Cruz 82, suppl 4 (1987): 193–95. http://dx.doi.org/10.1590/s0074-02761987000800033.

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Afifi, A. A., and A. A. Ahmed. "The Efficiency of Two Nile Fishes as Biocontrol Agents Against Different Stages of Schistosomiasis Intermediate Host." Journal of The Faculty of Science and Technology, no. 5 (October 5, 2018): 4–8. http://dx.doi.org/10.52981/jfst.vi5.359.

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The present investigation is dealing with the biological control of schistosome intermediate host, two Nile fishes Debs (Labeo niloticus) and the Nile Bulti or Tilabia (Cyrinus carbio) were selected to determine their efficiency to control schistosomiasis intermediate host (snails). Six laboratory sets of experiments were designed, three for Bulinus truncatus and other three for Biomphalaria pfeifferi. The first set in each snail species were control group, while the other two provided with the two Nile fishes, to investigate the efficiency of the selected biocontrol agents. In control set, gradual reduction of egg-masses, neonates and adult snails of both schistosomiasis snails. Compared with the control set, the two fishes verified to be highly efficient predators against egg-masses and neonates of the two snails (P < 0.001). While in case of the adults of both species reduced also very gradually.

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Cribb, TH. "Life-Cycle and Biology of Prototransversotrema-Steeri Angel, 1969 (Digenea, Transversotrematidae)." Australian Journal of Zoology 36, no. 2 (1988): 111. http://dx.doi.org/10.1071/zo9880111.

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A population of Prototransversotrema steeri Angel, 1969 is recorded from the introduced fish Gambusia affinis and the native species Pseudomugil signifer and Mugil cephalus in fresh water in Queensland, Australia. Adults of P. steeri are considerably smaller than adults previously described from marine fish. This appears to be a host-related phenomenon, possibly reflecting the size of the subscale niche offered by the host. The intermediate host is Posticobia brazieri, a hydrobiid snail. It is suggested that different hydrobiid snails may act as intermediate hosts in other parts of Australia. The miracidium develops into a mother sporocyst which produces a single mother redia. Mother rediae produce daughter rediae which may produce further daughter rediae or cercariae. Cercariae emerge from the redia while still embryonic and develop independently in the tissues of the snail. Upon emergence the cercariae attach directly to the definitive host and commence egg-production within 6 days. Gambusia affinis, Xiphophorus rnaculatus, X. helleri, Craterocephalus marjoriae and Mugil cephalus were all infected experimentally. I discuss various theories concerning the phylogenetic position of the Transverso- trematidae within the Digenea and conclude that the family occupies an isolated position not closely allied with any other group.

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TCHUEM TCHUENTÉ, L. A., V. R. SOUTHGATE, A. THÉRON, J. JOURDANE, A. LY, and B. GRYSEELS. "Compatibility of Schistosoma mansoni and Biomphalaria pfeifferi in Northern Senegal." Parasitology 118, no. 6 (June 1999): 595–603. http://dx.doi.org/10.1017/s0031182099004345.

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The construction of the Diama dam on the Senegal River and the ensuing ecological changes have led to a massive outbreak of Schistosoma mansoni infection in Northern Senegal, associated with very high intensity of infections, due to extremely intense transmission. The vectorial capacity of Biomphalaria pfeifferi from Ndombo, near Richard-Toll was investigated in order to assess the role of the snail–parasite relationship in this particular epidemiological situation. The results revealed an unusually high compatibility between the Senegalese S. mansoni strain and its local snail intermediate host, B. pfeifferi. The snail infection rate after exposure to a single miracidium per snail was 87%. The cercarial production of infected snails was very high, with a mean total production of 50456 cercariae per snail. No significant difference was found in the total cercarial output between snails exposed to 1 miracidium and those exposed to 5 miracidia. The increase in the rate of cercarial output was significantly greater in snails exposed to 5 miracidia, but there was a higher mortality in this group. The chronobiological cercarial production pattern showed a peak around mid-day. The implications of these findings on the epidemiology of schistosomiasis in Northern Senegal are discussed.

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Dar, Y., P. Vignoles, D. Rondelaud, and G. Dreyfuss. "Role of the lymnaeid snailPseudosuccinea columellain the transmission of the liver flukeFasciola hepaticain Egypt." Journal of Helminthology 89, no. 6 (May 27, 2014): 699–706. http://dx.doi.org/10.1017/s0022149x14000406.

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AbstractExperimental infections of three EgyptianPseudosuccinea columellapopulations with sympatric miracidia ofFasciolasp., coming from cattle- or sheep-collected eggs, were carried out to determine the capacity of this lymnaeid to support larval development of the parasite. Using microsatellite markers, the isolates of Egyptian miracidia were identified asFasciola hepatica. Apart from being independent of snail origin, prevalences ranging from 60.4 to 75.5% in snails infected with five miracidia ofF. hepaticawere significantly higher than values of 30.4 to 42.2% in snails with bi-miracidial infections. The number of metacercariae ranged from 243 to 472 per cercarial-shedding snail and was independent of snail origin, parasite origin and miracidial dose used for infection. IfP. columellawas subjected to two successive bi-miracidial infections withF. hepatica, prevalence of infection was 63.3%, with a mean of 311 metacercariae per snail. These values were clearly greater than those already reported forRadix natalensisinfected with the same parasite and the same protocol. Successful experimental infection ofP. columellawithF. hepaticasuggests that this lymnaeid snail is an important intermediate host for the transmission of fascioliasis in Egypt.

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Duffy, Michael S., Deanne K. Cevasco, Dante S. Zarlenga, Woraporn Sukhumavasi, and Judith A. Appleton. "Cathepsin B Homologue at the Interface between a Parasitic Nematode and Its Intermediate Host." Infection and Immunity 74, no. 2 (February 2006): 1297–304. http://dx.doi.org/10.1128/iai.74.2.1297-1304.2006.

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ABSTRACT Parelaphostrongylus tenuis is a parasitic nematode that causes a debilitating neurologic disease in many North American cervids and domestic livestock species. We produced a PCR-based cDNA library from infective larvae (L3) in order to identify molecules that mediate parasitism. A dominant 1,250-bp amplicon encoded a homologue of cathepsin B cysteine proteases. The sequence incorporated a C29G substitution in the putative active site. Antibodies generated against a recombinant form detected the native protein (PtCPR-1) in Western blot assays of L3, but not adult worm, extracts. Immunohistochemical methods revealed that PtCPR-1 synthesis was restricted to larval stages within the snail intermediate host (Triodopsis sp.), beginning as early as 2 days postinfection (dpi) of snails. The protein was present in the intestine and luminal contents and was lost from larvae over time. Concurrent studies showed that larvae induced an immune response in snails beginning at 1 dpi. Layers of hemocytes encapsulated larvae immediately after infection, and granuloma-like structures formed around parasites in chronic infections. Loss of PtCPR-1 from L3 and its accumulation in host tissues coincided with degeneration of granuloma architecture 90 to 105 dpi. Fully developed L3 emerged from the snail at this time. Our data implicate PtCPR-1 in larval development and possibly in the emergence of P. tenuis from the intermediate host. Emerged L3 survived desiccation and cold stress, suggesting that they could remain infectious in the environment. Molecules promoting emergence would facilitate dispersal of L3 and increase the likelihood of transmission to definitive hosts.

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Mendes, E. A., W. S. Lima, and A. L. de Melo. "Development ofFasciola hepaticainLymnaea columellainfected with miracidia derived from cattle and marmoset infections." Journal of Helminthology 82, no. 1 (March 2008): 81–84. http://dx.doi.org/10.1017/s0022149x07873585.

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AbstractThe development ofFasciola hepaticafrom two species of definitive hosts, i.e. cattle (Bos taurus) and a marmoset (Callithrix penicillata) in the snailLymnaea columellawas determined based on the production of rediae and cercariae and snail survival rate. More rediae and cercariae at 60–74 days post-infection were produced by snails infected by cattle-derived miracidia (cattle group) than by those infected by marmoset-derived miracidia (marmoset group). Among theL. columellaparasitized by the marmoset group, the survival rate and the percentage of positive snails were higher than among those parasitized by the cattle group. Eggs ofF. hepaticareleased in cattle faeces were significantly bigger than those released in marmoset faeces. Miracidia originating from parasites that completed their development in cattle were more efficient in infecting the intermediate host. These results suggest that vertebrate-host origin influences the eggs produced by the parasite and the infection rates in the snail hostL. columella.

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Bachtel, Rebecca Z., Matthew Rittenhouse, Gregory J. Sandland, and Jennifer A. H. Koop. "Infection patterns of trematodes across size classes of an invasive snail species using field and laboratory studies." Parasitology 146, no. 4 (September 27, 2018): 438–44. http://dx.doi.org/10.1017/s0031182018001646.

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AbstractIn the Upper Mississippi River Region, invasive faucet snails (Bithynia tentaculata) and their trematode parasites have been implicated in more than 182 000 waterfowl deaths since 1996. Estimating transmission potential depends on accurate assessments of susceptible host population size. However, little is known about the mechanisms underlying snail–host susceptibility in this system. Prior field studies suggest that very small, likely young, faucet snails are less suitable secondary intermediate hosts. Here, we test whether the patterns observed in the field are because small snails (1) are refractory to infection by cercariae, (2) die from infection and are removed from sampled populations, and/or (3) are not preferred by cercariae. Our own field collections were consistent with the observation that smaller faucet snails exhibit lower metacercarial infection prevalence and abundance than larger snails. However, laboratory-based experiments show that smaller snails were actually more susceptible to infection than larger snails. Moreover, the smallest snail size class had significantly higher mortality than larger snails following infection, which may explain their reduced infection levels observed in the field. Our study demonstrates the importance of pairing field and laboratory studies to better understand mechanisms underlying patterns of infection.

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DAI, JIAN-RONG, YOU-ZI LI, WEI WANG, YUN-TIAN XING, GUO-LI QU, and YOU-SHENG LIANG. "Resistance to niclosamide in Oncomelania hupensis, the intermediate host of Schistosoma japonicum: should we be worried?" Parasitology 142, no. 2 (July 8, 2014): 332–40. http://dx.doi.org/10.1017/s0031182014000870.

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SUMMARYAs the currently only available molluscicide, niclosamide has been widely used for snail control for over 2 decades in China. There is therefore a concern about the emergence of niclosamide-resistant snail populations following repeated, extensive use of the chemical. The purpose of this study was to investigate the likelihood of niclosamide resistance in Oncomelania hupensis in China. Active adult O. hupensis snails derived from 20 counties of 10 schistosomiasis-endemic provinces of China, of 10 snails in each drug concentration, were immersed in solutions of 1, 0·5, 0·25, 0·125, 0·063, 0·032, 0·016 and 0·008 mg L−1 of a 50% wettable powder of niclosamide ethanolamine salt (WPN) for 24 and 48 h at 25 °C, and the median lethal concentration (LC50) was estimated. Then, the 24- and 48-h WPN LC50 values were compared with those determined in the same sampling sites in 2002. The results indicated that the 24- and 48-h WPN LC50 values for O. hupensis were not significantly different from those determined in 2002 (P = 0·202 and 0·796, respectively). It is concluded that the current sensitivity of O. hupensis to niclosamide has not changed after more than 2 decades of repeated, extensive application in the main endemic foci of China, and there is no evidence of resistance to niclosamide detected in O. hupensis.

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Perez-Saez, Javier, Theophile Mande, Natalie Ceperley, Enrico Bertuzzo, Lorenzo Mari, Marino Gatto, and Andrea Rinaldo. "Hydrology and density feedbacks control the ecology of intermediate hosts of schistosomiasis across habitats in seasonal climates." Proceedings of the National Academy of Sciences 113, no. 23 (May 9, 2016): 6427–32. http://dx.doi.org/10.1073/pnas.1602251113.

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We report about field and theoretical studies on the ecology of the aquatic snails (Bulinus spp. and Biomphalaria pfeifferi) that serve as obligate intermediate hosts in the complex life cycle of the parasites causing human schistosomiasis. Snail abundance fosters disease transmission, and thus the dynamics of snail populations are critically important for schistosomiasis modeling and control. Here, we single out hydrological drivers and density dependence (or lack of it) of ecological growth rates of local snail populations by contrasting novel ecological and environmental data with various models of host demography. Specifically, we study various natural and man-made habitats across Burkina Faso’s highly seasonal climatic zones. Demographic models are ranked through formal model comparison and structural risk minimization. The latter allows us to evaluate the suitability of population models while clarifying the relevant covariates that explain empirical observations of snail abundance under the actual climatic forcings experienced by the various field sites. Our results link quantitatively hydrological drivers to distinct population dynamics through specific density feedbacks, and show that statistical methods based on model averaging provide reliable snail abundance projections. The consistency of our ranking results suggests the use of ad hoc models of snail demography depending on habitat type (e.g., natural vs. man-made) and hydrological characteristics (e.g., ephemeral vs. permanent). Implications for risk mapping and space-time allocation of control measures in schistosomiasis-endemic contexts are discussed.

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Diakité, Nana R., Konan G. N'Zi, Mamadou Ouattara, Jean T. Coulibaly, Jasmina Saric, Patrick K. Yao, Jan Hattendorf, Jürg Utzinger, and Eliézer K. N'Goran. "Association of riverine prawns and intermediate host snails and correlation with human schistosomiasis in two river systems in south-eastern Côte d'Ivoire." Parasitology 145, no. 13 (September 24, 2018): 1792–800. http://dx.doi.org/10.1017/s003118201800135x.

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AbstractThe current emphasis of schistosomiasis control is placed on preventive chemotherapy using praziquantel. However, reinfection may occur rapidly in the absence of complementary interventions. Recent studies from Senegal suggest that predatory prawns might feed on intermediate host snails and thus impact on schistosomiasis transmission. We designed a study with four repeated cross-sectional surveys pertaining to prawns and snails, coupled with a single cross-sectional parasitological survey among humans. We assessed for potential associations between the presence/density of prawns and snails and correlation withSchistosomainfection in a composite sample of school-aged children and adults. The study was carried out between October 2015 and December 2016 in 24 villages located near the Agnéby and Mé coastal river systems in south-eastern Côte d'Ivoire. At each site, snails and prawns were collected, and in each village, 150 individuals were subjected to stool and urine examination for the diagnosis ofSchistosoma mansoniandS. haematobium. We found peaks of relative abundance of intermediate host snails in the villages of the Agnéby River system, while predatory prawns were predominantly recorded in the Mé River system. A negative association was observed between intermediate host snail densities and riverine prawns; however, no pattern was found between this trend in the predator–prey relationship and the prevalence of human schistosomiasis.

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Lowenberger, C. A., and M. E. Rau. "Plagiorchis elegans: emergence, longevity and infectivity of cercariae, and host behavioural modifications during cercarial emergence." Parasitology 109, no. 1 (July 1994): 65–72. http://dx.doi.org/10.1017/s0031182000077775.

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SUMMARYWe investigated changes in the behaviour of Stagnicola elodes associated with the emergence of Plagiorchis elegans cercariae. Within 15 min of the reduction in light intensity, which triggered the onset of cercarial emergence, infected snails moved to the top of the water column and remained there for 2–3 h. Seventy-nine percent of all cercariae that emerged from the snail did so during this period. Uninfected snails showed no such behavioural changes following the change in light intensity. Cercariae were released in a dense cloud around the snail at the water surface and dispersed passively. Within 3–4 h more than 80% of all cercariae had settled in the bottom 5 cm of the water column. The infectivity of cercariae increased from less than 20% upon emergence from the snail to greater than 75% 4–6 h post-emergence, and then declined steadily to below 5% by 24 h post-emergence. Cercarial longevity was greater than 30 h and exceeded the period of infectivity. This may be related to steadily falling endogenous glycogen levels. A delay in attaining maximum infectivity may represent an adaptive mechanism allowing time for cercarial dissemination, thus reducing superinfection, and subsequent parasite-associated mortality, of second intermediate hosts.

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Katz, Naftale, Neusa Araújo, Paulo Marcos Zech Coelho, Carlos Medicis Morel, Ana Rosa Linde-Arias, Takeshi Yamada, Yuki Horimatsu, Koh Suzuki, Toshiaki Sunazuka, and Satoshi Ōmura. "Ivermectin efficacy against Biomphalaria, intermediate host snail vectors of Schistosomiasis." Journal of Antibiotics 70, no. 5 (March 15, 2017): 680–84. http://dx.doi.org/10.1038/ja.2017.31.

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Mouahid, Gabriel, Anne Rognon, Ronaldo de Carvalho Augusto, Patrick Driguez, Kathy Geyer, Shannon Karinshak, Nelia Luviano, et al. "Transplantation of schistosome sporocysts between host snails: A video guide." Wellcome Open Research 3 (January 9, 2018): 3. http://dx.doi.org/10.12688/wellcomeopenres.13488.1.

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Schistosomiasis is an important parasitic disease, touching roughly 200 million people worldwide. The causative agents are different Schistosoma species. Schistosomes have a complex life cycle, with a freshwater snail as intermediate host. After infection, sporocysts develop inside the snail host and give rise to human dwelling larvae. We present here a detailed step-by-step video instruction in English, French, Spanish and Portuguese that shows how these sporocysts can be manipulated and transferred from one snail to another. This procedure provides a technical basis for different types of ex vivo modifications, such as those used in functional genomics studies.

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Wood, Chelsea L., Susanne H. Sokolow, Isabel J. Jones, Andrew J. Chamberlin, Kevin D. Lafferty, Armand M. Kuris, Merlijn Jocque, et al. "Precision mapping of snail habitat provides a powerful indicator of human schistosomiasis transmission." Proceedings of the National Academy of Sciences 116, no. 46 (October 28, 2019): 23182–91. http://dx.doi.org/10.1073/pnas.1903698116.

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Recently, the World Health Organization recognized that efforts to interrupt schistosomiasis transmission through mass drug administration have been ineffective in some regions; one of their new recommended strategies for global schistosomiasis control emphasizes targeting the freshwater snails that transmit schistosome parasites. We sought to identify robust indicators that would enable precision targeting of these snails. At the site of the world’s largest recorded schistosomiasis epidemic—the Lower Senegal River Basin in Senegal—intensive sampling revealed positive relationships between intermediate host snails (abundance, density, and prevalence) and human urogenital schistosomiasis reinfection (prevalence and intensity in schoolchildren after drug administration). However, we also found that snail distributions were so patchy in space and time that obtaining useful data required effort that exceeds what is feasible in standard monitoring and control campaigns. Instead, we identified several environmental proxies that were more effective than snail variables for predicting human infection: the area covered by suitable snail habitat (i.e., floating, nonemergent vegetation), the percent cover by suitable snail habitat, and size of the water contact area. Unlike snail surveys, which require hundreds of person-hours per site to conduct, habitat coverage and site area can be quickly estimated with drone or satellite imagery. This, in turn, makes possible large-scale, high-resolution estimation of human urogenital schistosomiasis risk to support targeting of both mass drug administration and snail control efforts.

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Schjetlein, J., and A. Skorping. "The temperature threshold for development of Elaphostrongylus rangiferi in the intermediate host: an adaptation to winter survival?" Parasitology 111, no. 1 (July 1995): 103–10. http://dx.doi.org/10.1017/s0031182000064659.

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SUMMARYTo test the hypothesis that the relatively high developmental temperature threshold of the parasitic nematode Elaphostrongylus rangiferi in the intermediate snail host is an adaptation to minimize larval mortality during winter, an experiment was set up in which snails of the species Arianta arbustorum were experimentally infected with the parasite. The snails were divided into 3 groups known to contain 1st, 2nd or 3rd-stage larvae, and incubated at 3 °C for an experimental period of 18 weeks. First-stage larvae showed a significantly higher survival rate within snails than 2nd or 3rd-stage larvae. We also found that snails carrying 1st-stage larvae survived better than snails with other larval stages. It is concluded that if the nematode has started development before the hibernation, this has a real and significant effect on the risk of dying. The high developmental threshold is therefore likely to be an adaptation to reduce the chance of hibernating as developing larvae during long periods of low temperatures.

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de JONG-BRINK, M., M. BERGAMIN-SASSEN, and M. SOLIS SOTO. "Multiple strategies of schistosomes to meet their requirements in the intermediate snail host." Parasitology 123, no. 7 (November 2001): 129–41. http://dx.doi.org/10.1017/s0031182001008149.

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The results of the studies on our model combination Trichobilharzia ocellata–Lymnaea stagnalis, presented in this review, lead to the conclusion that schistosomes use multiple strategies to reach their goals, i.e. to propagate and to continue their life cycle. They have to escape from being attacked by the internal defence system (IDS) of the snail host and to profoundly affect the host's energy flow, of which reproduction and growth are the main determinants, for their own benefit. These physiological changes they establish mainly by interfering with the two regulatory systems in the snail host, the IDS and the neuroendocrine system (NES). Moreover, these two regulatory systems clearly interact with each other. Parasitic E/S products affect the host's IDS both in a direct and an indirect way. The neuropeptides or neuropeptide-like substances that are secreted by parasite glands into the host directly suppress haemocyte activity in the snail. The indirect effects include effects of (1) peptides from connective tissue cells and (2) neuropeptides from NES and/or IDS. Parasitic E/S products also induce the effects on energy flow in the host. These E/S products act either directly on a target, as shown for the inhibiting effect of the parasite on the development of the male copulation organ, or on the NES regulating reproductive activity, e.g. on gene expression. Indirect effects of E/S products on the NES (hormone-receptor interaction, electrical activity) are mediated by a factor from connective tissue cells, presumably belonging to the IDS. The physiological changes in the snail host are obviously of vital importance for the parasites, since they make use of different strategies to bring them about.

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McCarthy, A. M. "Speciation of echinostomes: evidence for the existence of two sympatric sibling species in the complex Echinoparyphium recurvatum (von Linstow 1873) (Digenea: Echinostomatidae)." Parasitology 101, no. 1 (August 1990): 35–42. http://dx.doi.org/10.1017/s0031182000079725.

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SUMMARYEvidence for the existence of 2 first intermediate host-specific sibling species of the 45 collar-spined echinostome Echinoparyphium recurvatum is presented. Experimental studies on their life-cycles were carried out under controlled laboratory conditions. The two entities were found to be morphologically indistinguishable in all major respects, yet they exhibited distinct biological characteristics. One of the sibling species utilizes the freshwater lymnaeid pulmonate snail Lymnaea peregra as first intermediate host, and the adults occur in the anterior small intestine of the wildfowl experimental definitive host Anas platyrhynchos. The other utilizes the freshwater mesogastropod prosobranch snail Valvata piscinalis as first intermediate host, and the adults occur in the posterior small intestine and rectum of A. platyrhynchos. The existence of the two sibling species in sympatry may be explained by the fact that the life-cycles of the two forms represent two distinct cycles of transmission serving to reduce excessive competition between them.

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Pennance, Tom, John Archer, Elena Birgitta Lugli, Penny Rostron, Felix Llanwarne, Said Mohammed Ali, Amour Khamis Amour, et al. "Development of a Molecular Snail Xenomonitoring Assay to Detect Schistosoma haematobium and Schistosoma bovis Infections in their Bulinus Snail Hosts." Molecules 25, no. 17 (September 2, 2020): 4011. http://dx.doi.org/10.3390/molecules25174011.

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Schistosomiasis, a neglected tropical disease of medical and veterinary importance, transmitted through specific freshwater snail intermediate hosts, is targeted for elimination in several endemic regions in sub-Saharan Africa. Multi-disciplinary methods are required for both human and environmental diagnostics to certify schistosomiasis elimination when eventually reached. Molecular xenomonitoring protocols, a DNA-based detection method for screening disease vectors, have been developed and trialed for parasites transmitted by hematophagous insects, such as filarial worms and trypanosomes, yet few have been extensively trialed or proven reliable for the intermediate host snails transmitting schistosomes. Here, previously published universal and Schistosoma-specific internal transcribed spacer (ITS) rDNA primers were adapted into a triplex PCR primer assay that allowed for simple, robust, and rapid detection of Schistosoma haematobium and Schistosoma bovis in Bulinus snails. We showed this two-step protocol could sensitively detect DNA of a single larval schistosome from experimentally infected snails and demonstrate its functionality for detecting S. haematobium infections in wild-caught snails from Zanzibar. Such surveillance tools are a necessity for succeeding in and certifying the 2030 control and elimination goals set by the World Health Organization.

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Johnson, Pieter T. J., Peder J. Lund, Richard B. Hartson, and Timothy P. Yoshino. "Community diversity reduces Schistosoma mansoni transmission, host pathology and human infection risk." Proceedings of the Royal Society B: Biological Sciences 276, no. 1662 (January 20, 2009): 1657–63. http://dx.doi.org/10.1098/rspb.2008.1718.

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Global biodiversity loss and disease emergence are two of the most challenging issues confronting science and society. Recently, observed linkages between species-loss and vector-borne infections suggest that biodiversity may help reduce pathogenic infections in humans and wildlife, but the mechanisms underlying this relationship and its applicability to a broader range of pathogens have remained speculative. Here, we experimentally evaluated the effects of host community structure on transmission of the human pathogen, Schistosoma mansoni , which alternates between snail intermediate hosts and vertebrate definitive hosts. By manipulating parasite exposure and community diversity, we show that heterospecific communities cause a 25–50 per cent reduction in infection among snail hosts ( Biomphalaria glabrata ). Infected snails raised alongside non-host snails ( Lymnaea or Helisoma sp.) also produced 60–80 per cent fewer cercariae, suggesting that diverse communities could reduce human infection risk. Because focal host density was held constant during experiments, decreases in transmission resulted entirely from diversity-mediated pathways. Finally, the decrease in infection in mixed-species communities led to an increase in reproductive output by hosts, representing a novel example of parasite-mediated facilitation. Our results underscore the significance of community structure on transmission of complex life-cycle pathogens, and we emphasize enhanced integration between ecological and parasitological research on the diversity–disease relationship.

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JONES, C. S., A. E. LOCKYER, D. ROLLINSON, and L. R. NOBLE. "Molecular approaches in the study of Biomphalaria glabrata – Schistosoma mansoni interactions: linkage analysis and gene expression profiling." Parasitology 123, no. 7 (November 2001): 181–96. http://dx.doi.org/10.1017/s0031182001008174.

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Gene mapping and the generation of linkage groups are fundamental to an understanding of the organization and relationships of genes and marker sequences, providing a framework with which to investigate their association with traits of interest. The abundance of techniques available for generating polymorphic molecular markers, and recent advances in high throughput screening, have allowed the extension of map analysis to the tropical freshwater snail Biomphalaria glabrata, an important intermediate host for Schistosoma mansoni. Direct comparison of gene expression by differential display screening, without prior identification of candidate genes, can be combined with mapping to quantify the involvement of specific sequences in the schistosome resistance response, and other important host–parasite interactions. Here we discuss the application of current and emergent technologies to gene characterization and linkage analysis in snail–schistosome interactions. Preliminary results from the analysis of comparative gene expression in resistant and susceptible snails are also presented.

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Journal, Baghdad Science. "Use of Nicotiana tobaccum extractions as a molluscicide to the snail of Bulinus truncates." Baghdad Science Journal 6, no. 2 (June 7, 2009): 298–301. http://dx.doi.org/10.21123/bsj.6.2.298-301.

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Nicotiana tobaccum L (Solanacea) extracts are used as a mollusciede to the snail Bulinus truncatus the intermediate host of urinary Schistosomiasis. LC50 of the extracts to the snail with 24 hour was 3.27 ml/l? 48 hour was 3.33 ml/l? 72 hour was 2.67 ml/l and 96 hour was 2.28ml/l. This study showed the ability to use the leaf extracts in the control of this type of snail.

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Maciel, Marcel Gonçalves, Walter dos Santos Lima, Francisco Lazaro Moreira de Almeida, Leila Inês Aguiar Raposo Câmara Coelho, Guilherme Alfredo Novelino Araújo, Mariana Gomes Lima, Luiz Henrique Gonçalves Maciel, et al. "Cross-Sectional Serological Survey of Human Fascioliasis in Canutama Municipality in Western Amazon, Brazil." Journal of Parasitology Research 2018 (2018): 1–8. http://dx.doi.org/10.1155/2018/6823638.

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Background. Fascioliasis is an important parasitic disease. In the northern region of Brazil, a human parasite infection has been reported through a coprological survey. Eggs of Fasciola hepatica were found in fecal samples of 11 individuals. Knowledge of the infection in animals or the presence of snails is necessary to address the possibility of the parasite cycle occurrence in that region. The aim of this study was to describe the transmission of human fascioliasis in Canutama, Amazonas, in Western Amazonia, Brazil. Methods. Serological (ELISA and Western Blot, WB) and parasitological analyses were carried out in humans. In addition, the presence of the intermediate snail host within the community was examined. Results. A total of 434 human samples were included in the study, of which 36 (8.3%) were reactive by ELISA and 8 (1.8%) were reactive by WB. Fasciola hepatica eggs were found in one human sample. The occurrence of the intermediated host was recorded and 31/43 specimens were identified as Lymnaea columella. Conclusion. Canutama constitutes a focus of transmission of human fascioliasis. This study describes the first serological survey for human fascioliasis, as well as its simultaneous occurrence in human hosts and possible intermediates performed in northern Brazil.

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Nguyen, Karena H., Philipp H. Boersch-Supan, Rachel B. Hartman, Sandra Y. Mendiola, Valerie J. Harwood, David J. Civitello, and Jason R. Rohr. "Interventions can shift the thermal optimum for parasitic disease transmission." Proceedings of the National Academy of Sciences 118, no. 11 (March 8, 2021): e2017537118. http://dx.doi.org/10.1073/pnas.2017537118.

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Temperature constrains the transmission of many pathogens. Interventions that target temperature-sensitive life stages, such as vector control measures that kill intermediate hosts, could shift the thermal optimum of transmission, thereby altering seasonal disease dynamics and rendering interventions less effective at certain times of the year and with global climate change. To test these hypotheses, we integrated an epidemiological model of schistosomiasis with empirically determined temperature-dependent traits of the human parasite Schistosoma mansoni and its intermediate snail host (Biomphalaria spp.). We show that transmission risk peaks at 21.7 °C (Topt), and simulated interventions targeting snails and free-living parasite larvae increased Topt by up to 1.3 °C because intervention-related mortality overrode thermal constraints on transmission. This Topt shift suggests that snail control is more effective at lower temperatures, and global climate change will increase schistosomiasis risk in regions that move closer to Topt. Considering regional transmission phenologies and timing of interventions when local conditions approach Topt will maximize human health outcomes.

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MATSUDA, Hajime. "Mekong schistosomiasis and the intermediate host snail in the Mekong region." Medical Entomology and Zoology 63, no. 4 (2012): 269–76. http://dx.doi.org/10.7601/mez.63.269.

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Ohmae, Hiroshi, Yuzuru Iwanaga, Takeshi Nara, Hajime Matsuda, and Kazuo Yasuraoka. "Biological characteristics and control of intermediate snail host of Schistosoma japonicum." Parasitology International 52, no. 4 (December 2003): 409–17. http://dx.doi.org/10.1016/s1383-5769(03)00058-8.

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Abdel Aal, Shaimaa M., Jomana A. Ahmed, and Mousa A. M. Ismail. "The Antigenic Relationship between Schistosoma Mansoni and Its Intermediate Snail Host." Journal of the Egyptian Society of Parasitology 46, no. 3 (December 2016): 663–70. http://dx.doi.org/10.12816/0033987.

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ABDEL AAL, SHAIMAA, JOMANA AHMED, MOUSA ISMAIL, and SAHAR ABDEL MAOGOOD. "THE ANTIGENIC RELATIONSHIP BETWEEN SCHISTOSOMA MANSONI AND ITS INTERMEDIATE SNAIL HOST." Journal of the Egyptian Society of Parasitology 46, no. 3 (December 1, 2016): 663–70. http://dx.doi.org/10.21608/jesp.2016.88320.

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Journal articles on the topic 'Snail intermediate host'

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