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Journal ArticleDOI

Pattern of cercarial emergence of Schistosoma curassoni from Niger and comparison with three sympatric species of schistosomes.

01 Feb 1992-Journal of Parasitology (J Parasitol)-Vol. 78, Iss: 1, pp 61-63
TL;DR: The emergence pattern of Schistosoma curassoni cercariae from Bulinus umbilicatus, whose adult worms parasitize bovine, caprine, and ovine ungulates in Niger, is of a circadian type with a mean emission time at 0855 hr 1 hr 6 min, characteristic of the schistosome species parasitizing domestic or wild cattle as mentioned in this paper.
Abstract: The emergence pattern of Schistosoma curassoni cercariae from Bulinus umbilicatus, whose adult worms parasitize bovine, caprine, and ovine ungulates in Niger, is of a circadian type with a mean emission time at 0855 hr 1 hr 6 min, characteristic of the schistosome species parasitizing domestic or wild cattle. The comparison of this cercarial emergence pattern with those of the other 3 sympatric species of schistosomes (Schistosoma haematobium, Schistosoma bovis, and Schistosoma mansoni) shows a significant difference between the chronobiology of the cercariae infective for human and those infective for bovine hosts. This difference may improve epidemiological surveys based on snail prevalences by allowing the distinction between bulinids infected with human and bovine parasites.

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Citations
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Journal ArticleDOI
TL;DR: These findings highlight the capacity of local populations to participate actively in schistosomiasis control programs and the limitations of widespread drug treatment campaigns, and provide opportunities to reduce exposure while maintaining resource-dependent livelihoods.
Abstract: Human schistosomiasis is a snail-borne parasitic disease affecting more than 200 million people worldwide. Direct contact with snail-infested freshwater is the primary route of exposure. Water management infrastructure, including dams and irrigation schemes, expands snail habitat, increasing the risk across the landscape. The Diama Dam, built on the lower basin of the Senegal River to prevent saltwater intrusion and promote year-round agriculture in the drought-prone Sahel, is a paradigmatic case. Since dam completion in 1986, the rural population-whose livelihoods rely mostly on agriculture-has suffered high rates of schistosome infection. The region remains one of the most hyperendemic regions in the world. Because of the convergence between livelihoods and environmental conditions favorable to transmission, schistosomiasis is considered an illustrative case of a disease-driven poverty trap (DDPT). The literature to date on the topic, however, remains largely theoretical. With qualitative data generated from 12 focus groups in four villages, we conducted team-based theme analysis to investigate how perception of schistosomiasis risk and reported preventive behaviors may suggest the presence of a DDPT. Our analysis reveals three key findings: 1) rural villagers understand schistosomiasis risk (i.e., where and when infections occur), 2) accordingly, they adopt some preventive behaviors, but ultimately, 3) exposure persists, because of circumstances characteristic of rural livelihoods. These findings highlight the capacity of local populations to participate actively in schistosomiasis control programs and the limitations of widespread drug treatment campaigns. Interventions that target the environmental reservoir of disease may provide opportunities to reduce exposure while maintaining resource-dependent livelihoods.

15 citations


Cites background from "Pattern of cercarial emergence of S..."

  • ...Snails are known to shed parasites in daily cycles, which peak around noon for human schistosomes.(49,50) Although focus group participants did not articulate knowledge of the snail-borne nature of schistosomiasis transmission, they did recognize the diurnal patterns of risk and reported risk-mitigating behavior....

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Journal ArticleDOI
TL;DR: The cercarial emission patterns of three strigeid species, Ichthyocotylurus erraticus, I. variegatus and Apatemon gracilis, from experimentally infected natural hosts were found to exhibit rhythms that correlated with the light:dark cycle.
Abstract: Many digenean cercariae have been shown to emerge from their molluscan hosts with distinct shedding patterns that have enabled the discrimination of morphologically similar species, or even strains. In this study the cercarial emission patterns of three strigeid species, Ichthyocotylurus erraticus, I. variegatus and Apatemon gracilis, from experimentally infected natural hosts were found to exhibit rhythms that correlated with the light:dark cycle. Both Ichthyocotylurus spp. exhibited a diurnal pattern of release in which cercariae emerged during the light period. Each demonstrated a latent period before the liberation of large numbers of cercariae and yielded similar numbers of cercariae daily. These rhythms offered no means for the discrimination of these two morphologically similar species. A. gracilis cercariae demonstrated a very different circadian rhythm in which the majority emerged at the onset of darkness with no latent period, whereas the cercarial numbers released daily were far greater. Differences could be related to piscine host behaviour.

13 citations


Cites background from "Pattern of cercarial emergence of S..."

  • ...The amount of stimulation (or removal of inhibition) required may be minimal, emergence beginning almost simultaneously with the onset of light or darkness as occurs in Schistosoma curassoni Brumpt, 1931 and S. bovis (see Mouchet et al. 1992)....

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  • ...Mouchet et al. (1992) could discriminate between the cercariae of four sympatric species of Schistosoma Weinland, 1858 on this basis alone....

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Dissertation
01 Jan 1995
TL;DR: The project aims were to establish the identity of the forms occurring in British fishes, by applying discriminatory techniques to the experimentally reared life-stages to clarify species membership to these taxa and indeed the taxonomic position of the subgenus Apatemon (Apatemon).
Abstract: This study is concerned with two strigeid genera which utilise fish as their second intermediate host and piscivorous birds as a definitive host, i.e. Apatemon (Apatemon) Sudarikov, 1959 and Ichthyocotylurus Odening, 1969. Although the lifecycle has been ascertained for most Ichthyocotylurus spp., confusion and disagreement still exist as to the constituent species, while all of the life-stages have been described for only a single member of the subgenus Apatemon (Apatemon). In order to clarify species membership to these taxa and indeed the taxonomic position of the subgenus Apatemon (Apatemon) further information was required on the life-cycles and life-stages of these strigeids. Although, metacercariae from this family have been recorded from a variety of British fishes, confirmed records, i.e. those supported with life-cycle data, are limited to a single species. It was this lack of confidence in identifying metacercariae recovered from fishes and the lack of known good criteria for distinguishing the adults that prompted the present study. Collections of metacercariae from a variety of hosts and locations were made, from which all subsequent life-cycle stages were obtained. The project aims were to establish the identity of the forms occurring in British fishes, by applying discriminatory techniques to the experimentally reared life-stages. In addition to traditional methods, techniques with little previous application to these genera were used and included, scanning electron microscopy (SEM), chaetotaxy, principal components analysis (PCA), and karyology. Furthermore, behavioural aspects such as the release patterns of cercariae from their molluscan hosts were studied to investigate whether they would prove to be of diagnostic value. Metacercariae obtained from the sampling survey were tentatively identified, using all currently employed methods for their determination, i.e. morphology, nature of cyst, host and site specificities, as Ichthyocotylurus erraticus (Rudolphi, 1809), I. variegatus (Creplin, 1825), Apatemon gracilis (Rudolphi, 1819) and A. annuligerum (Nordmann, 1832). Material collected from Finland was considered to contain both Ichthyocotylurus spp. recovered in the U.K., as well as I. platycephalus (Creplin, 1825) and I. pileatus (Rudolphi, 1802). The Ichthyocotylurus spp. were found to be more host specific than A. gracilis, although A. annuligerum was considered oioxenic to perch Perea fluiatilis L. Records of I. erraticus from gwyniad Coregonus lavaretus (L.) and grayling Thymallus thymallus (L.), and A. gracilis from arctic charr Salvelinus alpinus (L.) constitute first listings from Britain. The large number of sensilla present on the body surface of these metacercariae, observed by SEM and chaetotaxy, precluded their diagnostic use. PCA was, however, found to be of value for distinguishing between species and determining morphological variation within a species. I. erraticus, I. variegatus and A. gracilis adults were successfully reared in experimental hosts using…

11 citations

Journal ArticleDOI
TL;DR: How resource competition among snails profoundly alters the link between infected snails, the target of control, and schistosome cercariae, the cause of human infections is demonstrated.
Abstract: Significance Predicting how ecological interactions among vectors or intermediate hosts of human parasites influence transmission potential to humans remains challenging. Here, we focus on human schistosomiasis and demonstrate how resource competition among snails profoundly alters the link between infected snails, the target of control, and schistosome cercariae, the cause of human infections. We integrated an individual-based bioenergetics model of snail and schistosome dynamics with experiments in artificial waterbodies and field observations to anticipate and explain how resource-sensitive schistosome infections and resource competition among snails interact to generate brief peaks in transmission potential when snail populations grow from low densities. A resource-explicit view of snail and schistosome dynamics could maximize the potential for snail control methods to contribute to control of schistosomiasis. Predicting and disrupting transmission of human parasites from wildlife hosts or vectors remains challenging because ecological interactions can influence their epidemiological traits. Human schistosomes, parasitic flatworms that cycle between freshwater snails and humans, typify this challenge. Human exposure risk, given water contact, is driven by the production of free-living cercariae by snail populations. Conventional epidemiological models and management focus on the density of infected snails under the assumption that all snails are equally infectious. However, individual-level experiments contradict this assumption, showing increased production of schistosome cercariae with greater access to food resources. We built bioenergetics theory to predict how resource competition among snails drives the temporal dynamics of transmission potential to humans and tested these predictions with experimental epidemics and demonstrated consistency with field observations. This resource-explicit approach predicted an intense pulse of transmission potential when snail populations grow from low densities, i.e., when per capita access to resources is greatest, due to the resource-dependence of cercarial production. The experiment confirmed this prediction, identifying a strong effect of infected host size and the biomass of competitors on per capita cercarial production. A field survey of 109 waterbodies also found that per capita cercarial production decreased as competitor biomass increased. Further quantification of snail densities, sizes, cercarial production, and resources in diverse transmission sites is needed to assess the epidemiological importance of resource competition and support snail-based disruption of schistosome transmission. More broadly, this work illustrates how resource competition can sever the correspondence between infectious host density and transmission potential.

11 citations

Journal ArticleDOI
TL;DR: Biochemical, age and environmental factors influencing cercarial host attraction and attachment behavior have been elucidated and will inform further development of devices for environmental surveillance and potentially improve cercariae exposure prevention strategies.

9 citations

References
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Book
01 Jan 1981

4,608 citations

Journal ArticleDOI
TL;DR: Viable hybrid parasites were produced in the laboratory and were maintained up until the F4 generation, Comparisons of egg morphology, surface structure of adult male worms and enzyme profiles have been made between experimental hybrid lines and field isolates.

59 citations

Journal ArticleDOI
TL;DR: Experimental crossbreeding between schistosomes with an early and those with a late cercarial shedding pattern demonstrates that the cercaria emergence rhythms of schistOSomes are genetically determined.
Abstract: Using two chronobiological variants ofSchistosoma mansoni (a blood fluke infecting man) from Guadeloupe (French West Indies), we carried out experimental crossbreeding between schistosomes with an early and those with a late cercarial shedding pattern. The results obtained on the F1 (intermediate shedding patterns) and F2 generations (early, intermediate, and late patterns) demonstrate that the cercarial emergence rhythms of schistosomes are genetically determined. This genetic variability is interpreted as a consequence of the selective pressure exerted by the two different hosts (man and rat) implicated in the life cycle ofS. mansoni from the Guadeloupean focus of schistosomiasis.

54 citations

Journal Article
TL;DR: A snail survey in various parts of the Senegal River Basin, including the SenegalRiver Basin, temporary rain-fed pools, swamps, irrigation canals and drains, ricefields and Lac de Guier was carried out, finding Bulinus guernei was the most common, occurring in permanent habitats, and Bulinus senegalensis occurring in laterite pools in the eastern part of the Middle Valley.

53 citations

Journal ArticleDOI
TL;DR: A comparative study on the development of Senegalese isolates of Schistosoma curassoni, S. haematobium and S. bovis in hamsters is reported, together with the compatibility of these parasites with Bulinus spp.
Abstract: A comparative study on the development of Senegalese isolates of Schistosoma curassoni, S. haematobium and S. bovis in hamsters is reported, together with the compatibility of these parasites with Bulinus spp. and enzymes of adult worms. The mean worm return from 35 hamsters exposed to 100 cercariae each of S. curassoni was 11·5%, and of these 54% were paired, the remainder were single males. The growth and maturation of the worms were recorded from 40 to 100 days. The cross-over point (when paired females are of the same length as paired males) was reached at 42 days post-infection when the worms averaged 13·7 mm in length. The majority of tissue eggs (84·5%) were recovered from the liver, compared with 11% in the colon, 2·5% in the caecum and 1·6% in the small intestine. Estimates of the fecundity of paired females averaged 167 eggs/day per female worm. Snail-infection experiments showed S. curassoni to be compatible with B. umbilicatus, marginally compatible with B. senegalensis and incompatible with B...

37 citations