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Moses J. Chimbari - One of the best experts on this subject based on the ideXlab platform.
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Simulation of population dynamics of Bulinus globosus: Effects of environmental temperature on production of Schistosoma haematobium cercariae.
PLOS Neglected Tropical Diseases, 2018Co-Authors: Chester Kalinda, Moses J. Chimbari, William E. Grant, Hsiao-hsuan Wang, Julius Nyerere Odhiambo, Samson MukaratirwaAbstract:Background Temperature is an important factor that influences the biology and ecology of intermediate host (IH) snails and the schistosome parasites they transmit. Although temperature shifts due to climate change has been predicted to affect the life history traits of IH snails and parasite production, the mechanisms of how this may affect parasite abundance and disease risks are still not clear. Materials and methods Using data from laboratory and field experiments, we developed a deterministic compartmental simulation model based on difference equations using a weekly time step that represented the life cycle of Bulinus globosus. We simulated snail population dynamics and the associated production of cercariae assuming current environmental temperatures as well as projected temperature increases of 1 °C and 2 °C. Results The model generated snail fecundity and survival rates similar to those observed in the laboratory and also produced reasonable snail population dynamics under seasonally varying temperatures representative of generally favorable environmental conditions. Simulated relative abundances of both snails and cercariae decreased with increasing environmental temperatures, with maximum snail abundances decreased by 14% and 27%, and maximum cercariae productions decreased by 8% and 17%, when temperatures were increased by 1 °C and 2 °C, respectively. Conclusion The results indicate that future rise in temperature due to climate change may alter the abundance of B. globosus and impact on the prevalence of schistosomiasis. Furthermore, increased temperatures may not linearly influence the abundance of S. haematobium. These results may have important implications for schistosomiasis control programmes in view of temperature driven changes in the life history traits of B. globosus and S. haematobium. Our study recommends that the use of deterministic models incorporating the effects of temperature on the life history traits of IH snails would be vital in understanding the potential impact of climate change on schistosomiasis incidences and prevalence.
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Influence of desiccation on the survival of Bulinus globosus under laboratory conditions
Taylor & Francis Group, 2018Co-Authors: Chester Kalinda, Moses J. Chimbari, Mokgadi P. Malatji, Samson MukaratirwaAbstract:Environmental changes are generally known to influence the distribution and abundance of schistosome intermediate host snails (IHs). However, the influence of hydrologic changes per ser on the length of survival of schistosome IHs is not fully understood. To explore how desiccation may influence the survival of Bulinus globosus, the main IHs of Schistosoma haematobium in southern Africa, we conducted a study under laboratory conditions where snails were subjected to periods of desiccation and their survival evaluated. Desiccation period from 28 to 49 days post-draining of water was associated with an increase in mortality of 33.2 and 42.4% in large (mean shell height 7.81 ± 0.44 mm) and small (mean shell height 5.94 ± 0.68 mm) B. globosus snails, respectively. Although the duration of desiccation had no effect on the depth of burrowing, large size snails burrowed deeper into the soil than small size snails. The LT50 and LT90 of snails designated as large (7.81 ± 0.44 mm) were 73.35 ± 10.32 and 110.61 ± 21.03 days, respectively. On the other hand, LT50 and LT90 for snails designated as small (5.94 ± 0.68 mm) were 59.64 ± 8.56 and 84.19 ± 12.09 days, respectively. The survival of B. globosus during desiccation depended on the size/age of the snail where large size snails aestivate and survive for a longer period by burrowing deeper into the soil. We therefore conclude that adult B. globosus may play a significant role in habitat recolonization after a period of drought which is a common phenomenon in schistosomiasis endemic areas when population crashes
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Influence of desiccation on the survival of Bulinus globosus under laboratory conditions
Journal of Freshwater Ecology, 2018Co-Authors: Chester Kalinda, Moses J. Chimbari, Mokgadi P. Malatji, Samson MukaratirwaAbstract:Environmental changes are generally known to influence the distribution and abundance of schistosome intermediate host snails (IHs). However, the influence of hydrologic changes per ser on the length of survival of schistosome IHs is not fully understood. To explore how desiccation may influence the survival of Bulinus globosus, the main IHs of Schistosoma haematobium in southern Africa, we conducted a study under laboratory conditions where snails were subjected to periods of desiccation and their survival evaluated. Desiccation period from 28 to 49 days post-draining of water was associated with an increase in mortality of 33.2 and 42.4% in large (mean shell height 7.81 ± 0.44 mm) and small (mean shell height 5.94 ± 0.68 mm) B. globosus snails, respectively. Although the duration of desiccation had no effect on the depth of burrowing, large size snails burrowed deeper into the soil than small size snails. The LT50 and LT90 of snails designated as large (7.81 ± 0.44 mm) were 73.35 ± 10.32 and 110...
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Effect of temperature on the Bulinus globosus — Schistosoma haematobium system
Infectious Diseases of Poverty, 2017Co-Authors: Chester Kalinda, Moses J. Chimbari, Samson MukaratirwaAbstract:Background Given that increase in temperature may alter host-parasite relationships, the anticipated rise in temperature due to global warming might change transmission patterns of certain diseases. However, the extent to which this will happen is not well understood. Methods Using a host-parasite system involving Bulinus globosus and Schistosoma haematobium , we assessed the effect of temperature on snail fecundity, growth, survival and parasite development under laboratory conditions. Results Our results show that temperature may have a non-linear effect on snail fecundity and snail growth. Snails maintained at 15.5 °C and 36.0 °C did not produce egg masses while those maintained at 25.8 °C laid 344 and 105 more egg masses than snails at 31.0 °C and 21.2 °C, respectively. Attainment of patency led to a reduction in egg mass production among the snails. However, the reduction in fecundity for snails maintained at 21.2 °C occurred before snails started shedding cercariae. Parasite development was accelerated at high temperatures with snails maintained at 31.0 °C reaching patency after three weeks. Furthermore, snail growth rate was highest at 25.8 °C while it was inhibited at 15.5 °C and reduced at 31.0 °C. Increase in temperature increased snail mortality rates. Snails maintained at 36.0 °C had the shortest survival time while those maintained at 15.5 °C had the longest survival time. Conclusions We concluded that temperature influences fecunxdity, growth, survival and parasite development in the snail and thus dictates the time it takes the parasite to complete the life cycle. This has implications on transmission of schistosomiasis in the context of global warming.
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Effect of temperature on the Bulinus globosus — Schistosoma haematobium system
Infectious Diseases of Poverty, 2017Co-Authors: Chester Kalinda, Moses J. Chimbari, Samson MukaratirwaAbstract:Given that increase in temperature may alter host-parasite relationships, the anticipated rise in temperature due to global warming might change transmission patterns of certain diseases. However, the extent to which this will happen is not well understood. Using a host-parasite system involving Bulinus globosus and Schistosoma haematobium, we assessed the effect of temperature on snail fecundity, growth, survival and parasite development under laboratory conditions. Our results show that temperature may have a non-linear effect on snail fecundity and snail growth. Snails maintained at 15.5 °C and 36.0 °C did not produce egg masses while those maintained at 25.8 °C laid 344 and 105 more egg masses than snails at 31.0 °C and 21.2 °C, respectively. Attainment of patency led to a reduction in egg mass production among the snails. However, the reduction in fecundity for snails maintained at 21.2 °C occurred before snails started shedding cercariae. Parasite development was accelerated at high temperatures with snails maintained at 31.0 °C reaching patency after three weeks. Furthermore, snail growth rate was highest at 25.8 °C while it was inhibited at 15.5 °C and reduced at 31.0 °C. Increase in temperature increased snail mortality rates. Snails maintained at 36.0 °C had the shortest survival time while those maintained at 15.5 °C had the longest survival time. We concluded that temperature influences fecunxdity, growth, survival and parasite development in the snail and thus dictates the time it takes the parasite to complete the life cycle. This has implications on transmission of schistosomiasis in the context of global warming.
Samson Mukaratirwa - One of the best experts on this subject based on the ideXlab platform.
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Simulation of population dynamics of Bulinus globosus: Effects of environmental temperature on production of Schistosoma haematobium cercariae.
PLOS Neglected Tropical Diseases, 2018Co-Authors: Chester Kalinda, Moses J. Chimbari, William E. Grant, Hsiao-hsuan Wang, Julius Nyerere Odhiambo, Samson MukaratirwaAbstract:Background Temperature is an important factor that influences the biology and ecology of intermediate host (IH) snails and the schistosome parasites they transmit. Although temperature shifts due to climate change has been predicted to affect the life history traits of IH snails and parasite production, the mechanisms of how this may affect parasite abundance and disease risks are still not clear. Materials and methods Using data from laboratory and field experiments, we developed a deterministic compartmental simulation model based on difference equations using a weekly time step that represented the life cycle of Bulinus globosus. We simulated snail population dynamics and the associated production of cercariae assuming current environmental temperatures as well as projected temperature increases of 1 °C and 2 °C. Results The model generated snail fecundity and survival rates similar to those observed in the laboratory and also produced reasonable snail population dynamics under seasonally varying temperatures representative of generally favorable environmental conditions. Simulated relative abundances of both snails and cercariae decreased with increasing environmental temperatures, with maximum snail abundances decreased by 14% and 27%, and maximum cercariae productions decreased by 8% and 17%, when temperatures were increased by 1 °C and 2 °C, respectively. Conclusion The results indicate that future rise in temperature due to climate change may alter the abundance of B. globosus and impact on the prevalence of schistosomiasis. Furthermore, increased temperatures may not linearly influence the abundance of S. haematobium. These results may have important implications for schistosomiasis control programmes in view of temperature driven changes in the life history traits of B. globosus and S. haematobium. Our study recommends that the use of deterministic models incorporating the effects of temperature on the life history traits of IH snails would be vital in understanding the potential impact of climate change on schistosomiasis incidences and prevalence.
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Influence of desiccation on the survival of Bulinus globosus under laboratory conditions
Taylor & Francis Group, 2018Co-Authors: Chester Kalinda, Moses J. Chimbari, Mokgadi P. Malatji, Samson MukaratirwaAbstract:Environmental changes are generally known to influence the distribution and abundance of schistosome intermediate host snails (IHs). However, the influence of hydrologic changes per ser on the length of survival of schistosome IHs is not fully understood. To explore how desiccation may influence the survival of Bulinus globosus, the main IHs of Schistosoma haematobium in southern Africa, we conducted a study under laboratory conditions where snails were subjected to periods of desiccation and their survival evaluated. Desiccation period from 28 to 49 days post-draining of water was associated with an increase in mortality of 33.2 and 42.4% in large (mean shell height 7.81 ± 0.44 mm) and small (mean shell height 5.94 ± 0.68 mm) B. globosus snails, respectively. Although the duration of desiccation had no effect on the depth of burrowing, large size snails burrowed deeper into the soil than small size snails. The LT50 and LT90 of snails designated as large (7.81 ± 0.44 mm) were 73.35 ± 10.32 and 110.61 ± 21.03 days, respectively. On the other hand, LT50 and LT90 for snails designated as small (5.94 ± 0.68 mm) were 59.64 ± 8.56 and 84.19 ± 12.09 days, respectively. The survival of B. globosus during desiccation depended on the size/age of the snail where large size snails aestivate and survive for a longer period by burrowing deeper into the soil. We therefore conclude that adult B. globosus may play a significant role in habitat recolonization after a period of drought which is a common phenomenon in schistosomiasis endemic areas when population crashes
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Influence of desiccation on the survival of Bulinus globosus under laboratory conditions
Journal of Freshwater Ecology, 2018Co-Authors: Chester Kalinda, Moses J. Chimbari, Mokgadi P. Malatji, Samson MukaratirwaAbstract:Environmental changes are generally known to influence the distribution and abundance of schistosome intermediate host snails (IHs). However, the influence of hydrologic changes per ser on the length of survival of schistosome IHs is not fully understood. To explore how desiccation may influence the survival of Bulinus globosus, the main IHs of Schistosoma haematobium in southern Africa, we conducted a study under laboratory conditions where snails were subjected to periods of desiccation and their survival evaluated. Desiccation period from 28 to 49 days post-draining of water was associated with an increase in mortality of 33.2 and 42.4% in large (mean shell height 7.81 ± 0.44 mm) and small (mean shell height 5.94 ± 0.68 mm) B. globosus snails, respectively. Although the duration of desiccation had no effect on the depth of burrowing, large size snails burrowed deeper into the soil than small size snails. The LT50 and LT90 of snails designated as large (7.81 ± 0.44 mm) were 73.35 ± 10.32 and 110...
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Effect of temperature on the Bulinus globosus — Schistosoma haematobium system
Infectious Diseases of Poverty, 2017Co-Authors: Chester Kalinda, Moses J. Chimbari, Samson MukaratirwaAbstract:Background Given that increase in temperature may alter host-parasite relationships, the anticipated rise in temperature due to global warming might change transmission patterns of certain diseases. However, the extent to which this will happen is not well understood. Methods Using a host-parasite system involving Bulinus globosus and Schistosoma haematobium , we assessed the effect of temperature on snail fecundity, growth, survival and parasite development under laboratory conditions. Results Our results show that temperature may have a non-linear effect on snail fecundity and snail growth. Snails maintained at 15.5 °C and 36.0 °C did not produce egg masses while those maintained at 25.8 °C laid 344 and 105 more egg masses than snails at 31.0 °C and 21.2 °C, respectively. Attainment of patency led to a reduction in egg mass production among the snails. However, the reduction in fecundity for snails maintained at 21.2 °C occurred before snails started shedding cercariae. Parasite development was accelerated at high temperatures with snails maintained at 31.0 °C reaching patency after three weeks. Furthermore, snail growth rate was highest at 25.8 °C while it was inhibited at 15.5 °C and reduced at 31.0 °C. Increase in temperature increased snail mortality rates. Snails maintained at 36.0 °C had the shortest survival time while those maintained at 15.5 °C had the longest survival time. Conclusions We concluded that temperature influences fecunxdity, growth, survival and parasite development in the snail and thus dictates the time it takes the parasite to complete the life cycle. This has implications on transmission of schistosomiasis in the context of global warming.
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Effect of temperature on the Bulinus globosus — Schistosoma haematobium system
Infectious Diseases of Poverty, 2017Co-Authors: Chester Kalinda, Moses J. Chimbari, Samson MukaratirwaAbstract:Given that increase in temperature may alter host-parasite relationships, the anticipated rise in temperature due to global warming might change transmission patterns of certain diseases. However, the extent to which this will happen is not well understood. Using a host-parasite system involving Bulinus globosus and Schistosoma haematobium, we assessed the effect of temperature on snail fecundity, growth, survival and parasite development under laboratory conditions. Our results show that temperature may have a non-linear effect on snail fecundity and snail growth. Snails maintained at 15.5 °C and 36.0 °C did not produce egg masses while those maintained at 25.8 °C laid 344 and 105 more egg masses than snails at 31.0 °C and 21.2 °C, respectively. Attainment of patency led to a reduction in egg mass production among the snails. However, the reduction in fecundity for snails maintained at 21.2 °C occurred before snails started shedding cercariae. Parasite development was accelerated at high temperatures with snails maintained at 31.0 °C reaching patency after three weeks. Furthermore, snail growth rate was highest at 25.8 °C while it was inhibited at 15.5 °C and reduced at 31.0 °C. Increase in temperature increased snail mortality rates. Snails maintained at 36.0 °C had the shortest survival time while those maintained at 15.5 °C had the longest survival time. We concluded that temperature influences fecunxdity, growth, survival and parasite development in the snail and thus dictates the time it takes the parasite to complete the life cycle. This has implications on transmission of schistosomiasis in the context of global warming.
H Madsen - One of the best experts on this subject based on the ideXlab platform.
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Oral shelling of Bulinus spp. (Mollusca: Planorbidae) by the Lake Malaŵi cichlid, Metriaclima lanisticola (Pisces: Cichlidae)
Journal of Freshwater Ecology, 2011Co-Authors: Mary Lundeba, H Madsen, Jeremy S. Likongwe, Jay R. StaufferAbstract:Metriaclima lanisticola (a native cichlid of Lake Malaŵi) was studied under laboratory conditions to evaluate its potential as an agent for the biological control of schistosome intermediate host snails (i.e., Bulinus globosus, Bulinus nyassanus, and Bulinus tropicus). Crushing resistance of the three snail species was evaluated. M. lanisticola orally shelled snails of all species. Although there was no preference among species, fish preferred small to large snails. Crushing resistance of snails revealed that B. nyassanus had the highest resistance.
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Interactions between fish and snails in a Zimbabwe pond, with particular reference to Sargochromis codringtonii (Pisces: Cichlidae)
African Journal of Aquatic Science, 2010Co-Authors: Paul Makoni, Moses J. Chimbari, H MadsenAbstract:The impact of fishes on snail densities in a 100 x 12m pond was assessed from October 2000 to May 2002, using a fish exclosure experiment. Snail species included numerically dominant Bulinus globosus (ca 85%) as well as B. tropicus , Biomphalaria pfeifferi , Lymnaea natalensis and Melanoides tuberculata . Six fish species were present in the ponds prior to the start of the experiment; these were Tilapia rendalli , Oreochromis mossambicus , O . macrochir , Clarias gariepinus , Kneria auriculata and an unidentified Labeo species. At the beginning of the experiment 85 Sargochromis codringtonii were introduced into the pond. All fish species were periodically monitored by seine netting and the stomach contents of a sample of these was analysed. For the first five months of the experiment Bulinus globosus numbers were low, both inside the fish exclosures and in the adjacent control areas but, from April 2001 onwards, snail numbers inside the exclosures were consistently higher than those in the control areas. At the end of the experiment the density of B. globosus was 150.5snails m –2 in the exclosures and 4.7snails m –2 in the control areas. The other snail species showed the same trend, but the differences were less pronounced. Sargochromis codringtonii was the only fish species that was found to feed on snails and since this species became successfully established in the pond it was assumed to be responsible for the snail mortality outside the exclosures. Whilst this experimental design did not separate the effects of S . codringtonii from those of the other fish species, it does provide strong evidence that fish are important in the control of B . globosus , an intermediate host for schistosomiasis. African Journal of Aquatic Science 2005, 30(1): 45–48
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Schistosoma haematobium in Lake Malawi: susceptibility and molecular diversity of the snail hosts Bulinus globosus and B. nyassanus
Journal of Helminthology, 2008Co-Authors: Jay R. Stauffer, David Rollinson, H Madsen, Bonnie L. Webster, Kristin E. Black, Adrianus F. KoningsAbstract:Intermediate hosts of Schistosoma haematobium, the causative agent of urinary schistosomiasis, in Lake Malawi include: Bulinus globosus, a member of the B. africanus group and B. nyassanus, a diploid member of the B. truncatus/tropicus species complex. We compared genetic variability between isolates of S. haematobium from the southern part of the lake (Cape Maclear), where both B. globosus and B. nyassanus play a role as intermediate hosts, and isolates from the northern part, where only B. globosus is host. Data show that the S. haematobium isolates from these two areas of Lake Malawi cannot be distinguished using nuclear or mitochondrial sequences and are capable of cross-infections.
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Interactions between Bulinus globosus and B. tropicus (Gastropoda: Planorbidae) in a pond experiment in Zimbabwe
African Journal of Aquatic Science, 2007Co-Authors: B Ndlela, Moses J. Chimbari, H MadsenAbstract:Bulinus tropicus, which does not transmit Schistosoma haematobium, has been suggested for biological control of the schistosome intermediate host Bulinus globosus in Zimbabwe. The possible competition between B. tropicus and B. globosus was evaluated under semi-natural conditions in an enclosure experiment. The results of this study showed that B. tropicus was more prolific than B. globosus in enclosures containing both species However, the effect of B. tropicus on B. globosus population density was not statistically significant, suggesting that there was little or no competition between the two species.
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PREDATOR AVOIDANCE IN Bulinus globosus (MORELET, 1866) AND B. TROPICUS (KRAUSS, 1848) (GASTROPODA: PLANORBIDAE) EXPOSED TO PREDATORY AND NON-PREDATORY FISH
Journal of Molluscan Studies, 2004Co-Authors: Paul Makoni, Moses J. Chimbari, H MadsenAbstract:The cichlid fish, Sargochromis codringtonii, has been suggested for biological control of freshwater snails, especially those serving as intermediate hosts for schistosomes. This study examined the behaviour of two aquatic snail species, Bulinus globosus and Bulinus tropicus, when exposed to water conditioned (defined as water inhabited by fish) by either Sargochromis codringtonii, a molluscivore, or Tilapia rendalli (Boulenger, 1896), a herbivore, and when exposed to predation risk in the presence of a refuge. Both snail species crawled above the waterline to a greater extent when exposed to water conditioned by S. codringtonii than when exposed to water conditioned by T. rendalli, or unconditioned water. Although the number of snails leaving the water tended to increase with the density of S. codringtonii, this was not statistically significant. While Bulinus globosus elicited a greater response to water conditioned by feeding fish than to that conditioned by non-feeding fish, B. tropicus did not respond differently to the two treatments. The introduction of S. codringtonii into tanks with a refuge caused snails to move actively into the covered areas.
S K Chandiwana - One of the best experts on this subject based on the ideXlab platform.
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Mother-offspring data in a study of the mating system in a natural population of Bulinus globosus (Gastropoda: Planorbidae) in Zimbabwe
Genetics Research, 1996Co-Authors: Samson Mukaratirwa, S K Chandiwana, H. R. Siegismund, T. K. KristensenAbstract:The mating system of a natural population of Bulinus globosus from the Chiweshe area, Zimbabwe, was studied with mother—offspring data using isozyme genetic markers. The study was done in response to work on the genetic structure of this population which suggested a limited extent of cross-fertilization. Of the 24 adults whose progenies were analysed, at least 15 showed evidence of outcrossing and 9 had results consistent with selfing. These results show that the two modes of reproduction are important under natural conditions and the mating system of this population is considered to be ‘partially-selfing’.
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population biology of the freshwater snail Bulinus globosus in the zimbabwe highveld
Journal of Applied Ecology, 1990Co-Authors: M. E. J. Woolhouse, S K ChandiwanaAbstract:(1) The population dynamics of Bulinus globosus (Morelet), an intermediate host for urinary schistosomiasis, were studied at five river sites in the Zimbabwe highveld for between 4 and 28 months. (2) Adult snail abundance, recruitment and loss rates were monitored at weekly intervals using a mark-recapture method. Growth rates were measured on caged snails. (3) Variations in abundance of the snails were related to water temperature and water flow. Peak densities at the sites ranged from 0 01 to 0-6 snails (of shell length > 5 5 mm) litre-1. Survival rate was negatively correlated with temperature. Losses due to rainy season floods ranged up to 99 9%. (4) The relationship between recruitment rate and temperature was described by a bell curve, with peak recruitment at 20 6 'C. Recruitment rate varied between sites. This may have been due to differences in food quality (vegetation), water chemistry and/or densitydependent effects. (5) Growth rates were positively correlated with temperature. (6) Bulinus globosus populations had a temperature-dependent seasonal cycle, with rapid increases in abundance during periods of favourable temperatures. Floods or drought caused variable and irregular reductions in abundance. The implications of these opportunistic' population dynamics for snail control are discussed.
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Population dynamics model for Bulinus globosus, intermediate host for Schistosoma haematobium, in river habitats.
Acta Tropica, 1990Co-Authors: M. E. J. Woolhouse, S K ChandiwanaAbstract:A mathematical model is developed that describes the population dynamics of the freshwater snail Bulinus globosus, an intermediate host of Schistosoma haematobium. The model is developed from field data recording abundance changes, recruitment rates, and mortality rates for adult snails in river habitats in Zimbabwe. Rate of recruitment into the adult population is dependent on temperature, incorporating a time lag to allow for growth to adult size. Mortality rate is also a function of temperature. A temperature-dependent model provides a useful description of changes in abundance during the dry season. Long-term population fluctuations are greatly affected by spates (flooding) associated with heavy rainfall. An estimate is made of the frequency and effects of spates. A simulation model that allows variable annual rainfall predicts fluctuations in snail abundance over two orders of magnitude over timescales of ten or more years. The role of density-dependent factors and the long-term persistence of the population are discussed. B. globosus population dynamics can be described as 'density vague'.
David Rollinson - One of the best experts on this subject based on the ideXlab platform.
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Bulinus globosus (Planorbidae; Gastropoda) populations in the Lake Victoria basin and coastal Kenya show extreme nuclear genetic differentiation.
Acta Tropica, 2012Co-Authors: Silvester Nyakaana, J. Russell Stothard, David Rollinson, Bonnie L. Webster, Allen Nalugwa, Charles N. Lange, Aslak Jørgensen, Thomas K. KristensenAbstract:Bulinus globosus, a key intermediate host for Schistosoma haematobium that causes urinary schistosomiasis, is a hermaphroditic freshwater Planorbid snail species that inhabits patchy and transient water bodies prone to large seasonal variations in water availability. Although capable of self-fertilizing, this species has been reported to be preferentially out crossing. In this study, we characterized the population genetic structure of 19 B. globosus populations sampled across the Lake Victoria basin and coastal Kenya using four polymorphic microsatellite loci. Population genetic structure was characterized and quantified using FST statistics and Bayesian clustering algorithms. The four loci used in this study contained sufficient statistical power to detect low levels of population genetic differentiation and were highly polymorphic with the number of alleles per locus across populations ranging from 16 to 22. Average observed and expected heterozygosities across loci in each population ranged from 0.13 to 0.69 and from 0.39 to 0.79, respectively. Twenty-five of the seventy-six possible population-locus comparisons significantly deviated from Hardy–Weinberg equilibrium proportions after Bonferroni corrections, mostly due to the deficiency of heterozygotes. Significant genetic differentiation was observed between populations and Bayesian inferences identified 15 genetic clusters. The excess homozygosity, significant inbreeding and population genetic differentiation observed in B. globosus populations are likely to be due to the habitat patchiness, mating system and the proneness to cyclic extinction and recolonization in transient habitats.
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Schistosoma haematobium in Lake Malawi: susceptibility and molecular diversity of the snail hosts Bulinus globosus and B. nyassanus
Journal of Helminthology, 2008Co-Authors: Jay R. Stauffer, David Rollinson, H Madsen, Bonnie L. Webster, Kristin E. Black, Adrianus F. KoningsAbstract:Intermediate hosts of Schistosoma haematobium, the causative agent of urinary schistosomiasis, in Lake Malawi include: Bulinus globosus, a member of the B. africanus group and B. nyassanus, a diploid member of the B. truncatus/tropicus species complex. We compared genetic variability between isolates of S. haematobium from the southern part of the lake (Cape Maclear), where both B. globosus and B. nyassanus play a role as intermediate hosts, and isolates from the northern part, where only B. globosus is host. Data show that the S. haematobium isolates from these two areas of Lake Malawi cannot be distinguished using nuclear or mitochondrial sequences and are capable of cross-infections.
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Spatial and temporal population genetic survey of Bulinus globosus from Zanzibar: an intermediate host of Schistosoma haematobium
Journal of Zoology, 2007Co-Authors: Samantha Wilkinson, Aidan M. Emery, I. S. Khamis, A.f. Mgeni, J.r. Stothard, David RollinsonAbstract:In Zanzibar, the freshwater hermaphroditic snail Bulinus globosus is the intermediate host of the human parasite Schistosoma haematobium. To shed light on the patterns of genetic variation within Bu. globosus, variation at six polymorphic microsatellite loci was assessed to quantify spatial genetic structure within eight populations and temporal changes in a further four populations of the snails. Limited genetic variation was observed within populations, possibly reflecting both partial-selfing and fluctuations in population size. Although a statistically significant heterozygote deficiency was observed, Bu. globosus appears to be a preferential out-crosser, which was consistent with the absence of genotypic linkage disequilibria. Genetic variation across populations was substantial, illustrating significant isolation-by-distance on a regional scale and that gene flow was restricted to nearby populations. The temporal survey showed that levels of genetic variation and inbreeding changed over a 1-year period, consistent with field observations of seasonal change. The results strongly support a snail demographic model of population expansion and contraction throughout the year with habitats re-colonized by aestivating or surviving snails from local refugia. This model might help explain co-evolution of snails and schistosomes in Zanzibar as local populations of Bu. globosus have varying degrees of susceptibility to S. haematobium.
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Microsatellites in the freshwater snail Bulinus globosus (Gastropoda: Planorbidae) from Zanzibar
Molecular Ecology Notes, 2003Co-Authors: Aidan M. Emery, Nicola J. Loxton, J. Russell Stothard, Catherine S. Jones, Jenny Spinks, Julia Llewellyn-hughes, Leslie R. Noble, David RollinsonAbstract:Six microsatellite loci were isolated and characterized in Bulinus globosus, a freshwater snail with a wide distribution throughout sub-Saharan Africa. Bulinus globosus is an intermediate host of Schistosoma haematobium, the causative agent of human urinary schistosomiasis. Microsatellites were tested using 32 snails from four populations collected from Pemba and Unguja islands of Zanzibar. The microsatellite loci displayed relatively low levels of variation, with between two and five alleles per locus. FST estimates indicate that gene flow is low, as has previously been suggested for other species of Bulinus.
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Molecular characterization of Bulinus globosus and B. nasutus on Zanzibar, and an investigation of their roles in the epidemiology of Schistosoma haematobium
Transactions of The Royal Society of Tropical Medicine and Hygiene, 1997Co-Authors: J. Russell Stothard, David RollinsonAbstract:The ribosomal internal transcribed spacer (ITS) regions of both Bulinus globosus and B. nasutus from Zanzibar were amplified and restricted with 6 enzymes. Restriction products were separated by polyacrylamide gel electrophoresis and visualized by ethidium bromide staining. Considerable genetic variation was observed at 3 levels: (i) between species, (ii) among populations and (iii) among individuals. In addition, the 18S ribosomal deoxyribonucleic acid gene was amplified from both species and the products were also restricted with several enzymes. No variation was detected. Nucleotide diversity of the ITS was estimated to be approximately 0.019 for both species and nucleotide divergence between species was estimated to be 0.03. Restriction profiles differentiated these snail species and may prove useful for identification purposes. Only B. globosus populations were found to be naturally infected with Schistosoma haematobium. From laboratory infection studies of progeny snails, B. nasutus appeared to be refractory to S. haematobium, whereas certain B. globosus populations were susceptible to laboratory challenge.
