The Experts below are selected from a list of 261 Experts worldwide ranked by ideXlab platform
Wilfried Haas - One of the best experts on this subject based on the ideXlab platform.
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penetration of Cercariae into the living human skin schistosoma mansoni vs trichobilharzia szidati
Parasitology Research, 2009Co-Authors: Wilfried Haas, Simone HaeberleinAbstract:We studied the skin invasion of Schistosoma mansoni Cercariae by placing gamma-irradiated and nonirradiated Cercariae onto the living human skin and timing the behavior of 53 individuals. The skin invasion of S. mansoni was less efficient compared to the bird schistosome Trichobilharzia szidati. S. mansoni Cercariae crept longer on the skin after attachment until they started penetration movements (median of 43 s [range of 15 s-6.58 min]; T. szidati, median of 8 s [range of 0-80 s]). Subsequent to this longer exploratory phase, 74% penetrated into wrinkles (T. szidati 84%), 22% into the smooth skin surface (T. szidati 0%), and 4% into hair follicles (T. szidati 16%). The S. mansoni Cercariae needed, on average, 6.58 min (range of 1.57-13.13 min) for full entry, while T. szidati needed 4.0 min (range of 1.38-13.34 min); the fastest S. mansoni cercaria entered the skin within 94 s, while T. szidati entered within 83 s. Sixty percent of the S. mansoni Cercariae had the tails still attached when the bodies disappeared in the skin whereas all T. szidati Cercariae shed their tails within 0-105 s after the onset of penetration movements. The faster invasion of T. szidati may result from the more sophisticated host-finding mechanisms of this species. Regarding S. mansoni, cercarial dermatitis, as immediate skin response, developed after a sensitization period of 19 days.
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schistosoma mansoni human skin ceramides are a chemical cue for host recognition of Cercariae
Experimental Parasitology, 2008Co-Authors: Wilfried Haas, Simone Haeberlein, Sabina Behring, Eveline ZoppelliAbstract:Schistosoma mansoni Cercariae recognize the human host with a sequence of behavioral responses particularly to chemical host cues. After attaching to the skin surface, Cercariae are stimulated by so far unknown skin components to hold enduring contact with the skin and to start creeping towards entry sites. We studied the chemical stimulus of human skin for the cercarial enduring contact response by fractionation of human and pig skin surface extracts and offering the fractions to the Cercariae via membrane filters. Enduring contact was stimulated exclusively by ceramides, specific lipids of the uppermost skin layers. This chemical cue differs from the 6 chemical host signals used by S. mansoni Cercariae in other behavioral steps of host invasion, and thus underlines the specialization of S. mansoni Cercariae particularly in chemical host signals. All together, the enduring contact response of the Cercariae is, like the other phases of host invasion, well adapted to the chemical properties of human skin.
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swimming behaviour of schistosoma mansoni Cercariae responses to irradiance changes and skin attractants
Parasitology Research, 2008Co-Authors: Sebastian Brachs, Wilfried HaasAbstract:The swimming behaviour of many cercarial species is governed by sensitive responses to light and dark stimuli. We studied the effect of irradiance changes on swimming behaviour of Schistosoma mansoni Cercariae and found only insignificant responses. Decreasing light intensity results in a weak tendency of the Cercariae to start swimming movements, and increasing light intensity tends to inhibit the start of swimming. These responses seem not suitable to increase the transmission success. Whether the Cercariae show chemo-orientation towards human skin was studied by video-tracking their swimming movements around agar containing human-skin-surface extracts and when immersed into skin extracts. They showed no directed chemotactic orientation, as they did not correct their swimming paths in direction towards the skin-extract substrates, also not when shifting between forward and backward swimming. However, the Cercariae shifted more between backward and forward swimming and therewith increased their rate of change of direction. This response may support an accumulation around the skin substrates and could guide the Cercariae towards the host’s skin surface when they are already in close proximity to it.
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prevalence of Cercariae from lymnaea stagnalis snails in a pond system in southern germany
Parasitology Research, 2001Co-Authors: Christina Loy, Wilfried HaasAbstract:Lymnaea stagnalis snails were collected from 174 individual ponds of an extensive pond system in South Germany; 43,441 snails collected during 1980–2000 were examined for shedding Cercariae. The species richness (at least 18 species of Cercariae) and the high cercarial prevalence (at least 44.9%) may result from the high abundance and diversity of vertebrate and invertebrate hosts in the area. The mean prevalence (%± SEM) of most cercarial species increased from May–June to August–October, e.g. in Diplostomum spathaceum from 4.1% to 18.6%, in all echinostomatids from 5.6% to 18.0%, in Pseudechinoparyphium echinatum from 3.0% to 11.2%, in XiphidioCercariae from 2.2% to 13.4%, and the overall prevalence shifted from 13.7% to 53.5%. There was no change in the prevalence of the different cercarial species over the last 20 years. The agents of cercarial dermatitis showed a constant low prevalence, 0.17% in Trichobilharzia ocellata (43,441 L. stagnalis examined) and 0.24% in other Trichobilharzia species (4,245 Radix examined). Such low prevalences seem to be normal in areas where cercarial dermatitis occurs in humans.
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invasion of the vertebrate skin by Cercariae of trichobilharzia ocellata penetration processes and stimulating host signals
Parasitology Research, 1998Co-Authors: Wilfried Haas, Adrianus Van De RoemerAbstract:The penetration of Trichobilharzia ocellata Cercariae into the skin of their duck hosts was described using electron microscopy and histology. The behavior patterns of the Cercariae on their exposure to human skin differed only little from those known for Schistosoma mansoni Cercariae. After their attachment to living human skin the Cercariae crept to wrinkles within a mean of 8 s, and full penetration was achieved within a mean of 4.0 min (83 s to 13.3 min). Tail shedding occurred as early as within a mean of 6.5 s of the first penetration attempts. It was supported by a muscular sphincter at the cercarial hindbody. The skin-surface stimuli for cercarial penetration were contained in the lipid fraction of the duck and human skin surface; hydrophilic components were effective only in some T. ocellata isolates. The penetration-stimulating components of duck-skin lipids were exclusively free fatty acids with the same chemical characteristics known to stimulate penetration of Schistosoma species. Skin-surface lipids of the abnormal human host, with their higher fatty acid contents, stimulated higher cercarial penetration rates than did skin lipids of the natural duck host. Fatty acids as penetration stimuli may offer advantages for T. ocellata Cercariae by increasing the specificity for an invasion of terrestrial vertebrates, which is additionally determined by cholesterol and ceramides as signals for attachment and enduring contact behavior.
P J Hudson - One of the best experts on this subject based on the ideXlab platform.
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Transmission, infectivity and survival of Diplostomum spathaceum Cercariae.
Parasitology, 2003Co-Authors: A Karvonen, S Paukku, E T Valtonen, P J HudsonAbstract:SUMMARY The transmission dynamics of the Cercariae of Diplostomum spathaceum were investigated under laboratory conditions using Cercariae collected from naturally infected Lymnaea stagnalis. Cercariae were kept in a constant temperature of 20 xC and the survival and infectivity to naive young rainbow trout recorded at 3-h intervals until few Cercariae were alive. Mortality initially remained constant but increased rapidly after 20 h. While a model of constant mortality fitted the survival data, an age-dependent model provided a better fit and implied that Cercariae tended to carry similar quantities of resources and once these were exhausted the Cercariae died. Cercarial infectivity also showed an age-dependent pattern although infectivity tended (P=0 . 09) to increase with age over the first 6 h of life and then fall. The per capita transmission rate of Cercariae was investigated by experimentally infecting rainbow trout under standardized conditions, first with an increasing cercarial density and second, by keeping density constant but increasing numbers of Cercariae. The per capita transmission rate was frequency dependent and averaged 0 . 341/h (i0 . 036).
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Transmission, infectivity and survival of Diplostomum spathaceum Cercariae.
Parasitology, 2003Co-Authors: A Karvonen, S Paukku, E T Valtonen, P J HudsonAbstract:The transmission dynamics of the Cercariae of Diplostomum spathaceum were investigated under laboratory conditions using Cercariae collected from naturally infected Lymnaea stagnalis. Cercariae were kept in a constant temperature of 20 degrees C and the survival and infectivity to naïve young rainbow trout recorded at 3-h intervals until few Cercariae were alive. Mortality initially remained constant but increased rapidly after 20 h. While a model of constant mortality fitted the survival data, an age-dependent model provided a better fit and implied that Cercariae tended to carry similar quantities of resources and once these were exhausted the Cercariae died. Cercarial infectivity also showed an age-dependent pattern although infectivity tended (P = 0.09) to increase with age over the first 6 h of life and then fall. The per capita transmission rate of Cercariae was investigated by experimentally infecting rainbow trout under standardized conditions, first with an increasing cercarial density and second, by keeping density constant but increasing numbers of Cercariae. The per capita transmission rate was frequency dependent and averaged 0.341/h (+/- 0.036).
Michael R Templeton - One of the best experts on this subject based on the ideXlab platform.
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Chlorination of Schistosoma mansoni Cercariae.
PLoS neglected tropical diseases, 2020Co-Authors: Laura Braun, Fiona Allan, Aidan M Emery, Yasinta Daniel Sylivester, Meseret Dessalegne Zerefa, Muluwork Maru, Feleke Zewge, Safari Kinung'hi, Michael R TempletonAbstract:BACKGROUND Schistosomiasis is a water-based disease acquired through contact with cercaria-infested water. Communities living in endemic regions often rely on parasite-contaminated freshwater bodies for their daily water contact activities, resulting in recurring schistosomiasis infection. In such instances, water treatment can provide safe water on a household or community scale. However, to-date there are no water treatment guidelines that provide information on how to treat water containing schistosome Cercariae. Here, we rigorously test the effectiveness of chlorine against Schistosoma mansoni Cercariae. METHOD S. mansoni Cercariae were chlorinated using sodium hypochlorite under lab and field condition. The water pH was controlled at 6.5, 7.0 or 7.5, the water temperature at 20°C or 27°C, and the chlorine dose at 1, 2 or 3 mg/l. Experiments were conducted up to contact times of 45 minutes. 100 Cercariae were used per experiment, thereby achieving up to 2-log10 inactivations of Cercariae. Experiments were replicated under field conditions at Lake Victoria, Tanzania. CONCLUSION A CT (residual chlorine concentration x chlorine contact time) value of 26±4 mg·min/l is required to achieve a 2-log10 inactivation of S. mansoni Cercariae under the most conservative condition tested (pH 7.5, 20°C). Field and lab-cultivated Cercariae show similar chlorine sensitivities. A CT value of 30 mg·min/l is therefore recommended to disinfect cercaria-infested water, though safety factors may be required, depending on water quality and operating conditions. This CT value can be achieved with a chlorine residual of 1 mg/l after a contact time of 30 minutes, for example. This recommendation can be used to provide safe water for household and recreational water activities in communities that lack safe alternative water sources.
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determining the viability of schistosoma mansoni Cercariae using fluorescence assays an application for water treatment
PLOS Neglected Tropical Diseases, 2020Co-Authors: Laura Braun, Lucinda Hazell, Alexander J Webb, Fiona Allan, Aidan M Emery, Michael R TempletonAbstract:Background Schistosome Cercariae are the human-infectious stage of the Schistosoma parasite]. They are shed by snail intermediate hosts living in freshwater, and penetrate the skin of the human host to develop into schistosomes, resulting in schistosomiasis infection. Water treatment (e.g. filtration or chlorination) is one way of cutting disease transmission; it kills or removes Cercariae to provide safe water for people to use for activities such as bathing or laundry as an alternative to infested lakes or rivers. At present, there is no standard method for assessing the effectiveness of water treatment processes on Cercariae. Examining cercarial movement under a microscope is the most common method, yet it is subjective and time-consuming. Hence, there is a need to develop and verify accurate, high-throughput assays for quantifying cercarial viability. Method We tested two fluorescence assays for their ability to accurately determine cercarial viability in water samples, using S. mansoni Cercariae released from infected snails in the Schistosomiasis Collection at the Natural History Museum, London. These assays consist of dual stains, namely a vital and non-vital dye; fluorescein diacetate (FDA) and Hoechst, and FDA and Propidium Iodide. We also compared the results of the fluorescence assays to the viability determined by microscopy. Conclusion Both fluorescence assays can detect the viability of Cercariae to an accuracy of at least 92.2% ± 6.3%. Comparing the assays to microscopy, no statistically significant difference was found between the method’s viability results. However, the fluorescence assays are less subjective and less time-consuming than microscopy, and therefore present a promising method for quantifying the viability of schistosome Cercariae in water samples.
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the effectiveness of water treatment processes against schistosome Cercariae a systematic review
PLOS Neglected Tropical Diseases, 2018Co-Authors: Laura Braun, Jack E T Grimes, Michael R TempletonAbstract:Background Schistosomiasis is one of the most disabling neglected tropical diseases, ranking second in terms of years lived with disability. While treatment with the drug praziquantel can have immediate beneficial effects, reinfection can occur rapidly if people are in contact with cercaria-infested water. Water treatment for schistosomiasis control seeks to eliminate viable Cercariae from water, thereby providing safe alternative water supplies for recreational and domestic activities including laundry and bathing. This provision may reduce contact with infested water, which is crucial for reducing reinfection following chemotherapy and cutting schistosome transmission. Methodology A qualitative systematic review was carried out to summarize the existing knowledge on the effectiveness of water treatment in removing or inactivating human schistosome Cercariae. Four online databases were searched. Studies were screened and categorized into five water treatment processes: storage, heating, chlorination, filtration, and ultraviolet (UV) disinfection. Conclusions All five water treatment methods can remove or inactivate Cercariae in water, and hence produce cercaria-free water. However, reliable design guidelines for treating water do not exist as there are insufficient data. Overall, the review found that Cercariae are inactivated when storing water for 10–72 hours (depending on temperature), or with chlorination values of 3–30 mg-min/l. UV fluences between 3–60 mJ/cm2 may significantly damage or kill Cercariae, and sand filters with 0.18–0.35 mm grain size have been shown to remove Cercariae. This systematic review identified 67 studies about water treatment and schistosomiasis published in the past 106 years. It highlights the many factors that influence the results of water treatment experiments, which include different water quality conditions and methods for measuring key parameters. Variation in these factors limit comparability, and therefore currently available information is insufficient for providing complete water treatment design recommendations.
A Karvonen - One of the best experts on this subject based on the ideXlab platform.
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Transmission, infectivity and survival of Diplostomum spathaceum Cercariae.
Parasitology, 2003Co-Authors: A Karvonen, S Paukku, E T Valtonen, P J HudsonAbstract:SUMMARY The transmission dynamics of the Cercariae of Diplostomum spathaceum were investigated under laboratory conditions using Cercariae collected from naturally infected Lymnaea stagnalis. Cercariae were kept in a constant temperature of 20 xC and the survival and infectivity to naive young rainbow trout recorded at 3-h intervals until few Cercariae were alive. Mortality initially remained constant but increased rapidly after 20 h. While a model of constant mortality fitted the survival data, an age-dependent model provided a better fit and implied that Cercariae tended to carry similar quantities of resources and once these were exhausted the Cercariae died. Cercarial infectivity also showed an age-dependent pattern although infectivity tended (P=0 . 09) to increase with age over the first 6 h of life and then fall. The per capita transmission rate of Cercariae was investigated by experimentally infecting rainbow trout under standardized conditions, first with an increasing cercarial density and second, by keeping density constant but increasing numbers of Cercariae. The per capita transmission rate was frequency dependent and averaged 0 . 341/h (i0 . 036).
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Transmission, infectivity and survival of Diplostomum spathaceum Cercariae.
Parasitology, 2003Co-Authors: A Karvonen, S Paukku, E T Valtonen, P J HudsonAbstract:The transmission dynamics of the Cercariae of Diplostomum spathaceum were investigated under laboratory conditions using Cercariae collected from naturally infected Lymnaea stagnalis. Cercariae were kept in a constant temperature of 20 degrees C and the survival and infectivity to naïve young rainbow trout recorded at 3-h intervals until few Cercariae were alive. Mortality initially remained constant but increased rapidly after 20 h. While a model of constant mortality fitted the survival data, an age-dependent model provided a better fit and implied that Cercariae tended to carry similar quantities of resources and once these were exhausted the Cercariae died. Cercarial infectivity also showed an age-dependent pattern although infectivity tended (P = 0.09) to increase with age over the first 6 h of life and then fall. The per capita transmission rate of Cercariae was investigated by experimentally infecting rainbow trout under standardized conditions, first with an increasing cercarial density and second, by keeping density constant but increasing numbers of Cercariae. The per capita transmission rate was frequency dependent and averaged 0.341/h (+/- 0.036).
Laura Braun - One of the best experts on this subject based on the ideXlab platform.
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Chlorination of Schistosoma mansoni Cercariae.
PLoS neglected tropical diseases, 2020Co-Authors: Laura Braun, Fiona Allan, Aidan M Emery, Yasinta Daniel Sylivester, Meseret Dessalegne Zerefa, Muluwork Maru, Feleke Zewge, Safari Kinung'hi, Michael R TempletonAbstract:BACKGROUND Schistosomiasis is a water-based disease acquired through contact with cercaria-infested water. Communities living in endemic regions often rely on parasite-contaminated freshwater bodies for their daily water contact activities, resulting in recurring schistosomiasis infection. In such instances, water treatment can provide safe water on a household or community scale. However, to-date there are no water treatment guidelines that provide information on how to treat water containing schistosome Cercariae. Here, we rigorously test the effectiveness of chlorine against Schistosoma mansoni Cercariae. METHOD S. mansoni Cercariae were chlorinated using sodium hypochlorite under lab and field condition. The water pH was controlled at 6.5, 7.0 or 7.5, the water temperature at 20°C or 27°C, and the chlorine dose at 1, 2 or 3 mg/l. Experiments were conducted up to contact times of 45 minutes. 100 Cercariae were used per experiment, thereby achieving up to 2-log10 inactivations of Cercariae. Experiments were replicated under field conditions at Lake Victoria, Tanzania. CONCLUSION A CT (residual chlorine concentration x chlorine contact time) value of 26±4 mg·min/l is required to achieve a 2-log10 inactivation of S. mansoni Cercariae under the most conservative condition tested (pH 7.5, 20°C). Field and lab-cultivated Cercariae show similar chlorine sensitivities. A CT value of 30 mg·min/l is therefore recommended to disinfect cercaria-infested water, though safety factors may be required, depending on water quality and operating conditions. This CT value can be achieved with a chlorine residual of 1 mg/l after a contact time of 30 minutes, for example. This recommendation can be used to provide safe water for household and recreational water activities in communities that lack safe alternative water sources.
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determining the viability of schistosoma mansoni Cercariae using fluorescence assays an application for water treatment
PLOS Neglected Tropical Diseases, 2020Co-Authors: Laura Braun, Lucinda Hazell, Alexander J Webb, Fiona Allan, Aidan M Emery, Michael R TempletonAbstract:Background Schistosome Cercariae are the human-infectious stage of the Schistosoma parasite]. They are shed by snail intermediate hosts living in freshwater, and penetrate the skin of the human host to develop into schistosomes, resulting in schistosomiasis infection. Water treatment (e.g. filtration or chlorination) is one way of cutting disease transmission; it kills or removes Cercariae to provide safe water for people to use for activities such as bathing or laundry as an alternative to infested lakes or rivers. At present, there is no standard method for assessing the effectiveness of water treatment processes on Cercariae. Examining cercarial movement under a microscope is the most common method, yet it is subjective and time-consuming. Hence, there is a need to develop and verify accurate, high-throughput assays for quantifying cercarial viability. Method We tested two fluorescence assays for their ability to accurately determine cercarial viability in water samples, using S. mansoni Cercariae released from infected snails in the Schistosomiasis Collection at the Natural History Museum, London. These assays consist of dual stains, namely a vital and non-vital dye; fluorescein diacetate (FDA) and Hoechst, and FDA and Propidium Iodide. We also compared the results of the fluorescence assays to the viability determined by microscopy. Conclusion Both fluorescence assays can detect the viability of Cercariae to an accuracy of at least 92.2% ± 6.3%. Comparing the assays to microscopy, no statistically significant difference was found between the method’s viability results. However, the fluorescence assays are less subjective and less time-consuming than microscopy, and therefore present a promising method for quantifying the viability of schistosome Cercariae in water samples.
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the effectiveness of water treatment processes against schistosome Cercariae a systematic review
PLOS Neglected Tropical Diseases, 2018Co-Authors: Laura Braun, Jack E T Grimes, Michael R TempletonAbstract:Background Schistosomiasis is one of the most disabling neglected tropical diseases, ranking second in terms of years lived with disability. While treatment with the drug praziquantel can have immediate beneficial effects, reinfection can occur rapidly if people are in contact with cercaria-infested water. Water treatment for schistosomiasis control seeks to eliminate viable Cercariae from water, thereby providing safe alternative water supplies for recreational and domestic activities including laundry and bathing. This provision may reduce contact with infested water, which is crucial for reducing reinfection following chemotherapy and cutting schistosome transmission. Methodology A qualitative systematic review was carried out to summarize the existing knowledge on the effectiveness of water treatment in removing or inactivating human schistosome Cercariae. Four online databases were searched. Studies were screened and categorized into five water treatment processes: storage, heating, chlorination, filtration, and ultraviolet (UV) disinfection. Conclusions All five water treatment methods can remove or inactivate Cercariae in water, and hence produce cercaria-free water. However, reliable design guidelines for treating water do not exist as there are insufficient data. Overall, the review found that Cercariae are inactivated when storing water for 10–72 hours (depending on temperature), or with chlorination values of 3–30 mg-min/l. UV fluences between 3–60 mJ/cm2 may significantly damage or kill Cercariae, and sand filters with 0.18–0.35 mm grain size have been shown to remove Cercariae. This systematic review identified 67 studies about water treatment and schistosomiasis published in the past 106 years. It highlights the many factors that influence the results of water treatment experiments, which include different water quality conditions and methods for measuring key parameters. Variation in these factors limit comparability, and therefore currently available information is insufficient for providing complete water treatment design recommendations.
