Imperial College London

DrBonnieWebster

Faculty of Natural SciencesDepartment of Life Sciences

 
 
 
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bonnie.webster

 
 
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G29 Ground FloorMedical SchoolSt Mary's Campus

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Summary

 

Publications

Publication Type
Year
to

23 results found

Gower CM, Gouvras AN, Lamberton PHL, Deol A, Shrivastava J, Mutombo PN, Mbuh JV, Norton AJ, Webster BL, Stothard JR, Garba A, Lamine MS, Kariuki C, Lange CN, Mkoji GM, Kabatereine NB, Gabrielli AF, Rudge JW, Fenwick A, Sacko M, Dembele R, Lwambo NJS, Tchuente L-AT, Rollinson D, Webster JPet al., 2013, Population genetic structure of Schistosoma mansoni and Schistosoma haematobium from across six sub-Saharan African countries: Implications for epidemiology, evolution and control, ACTA TROPICA, Vol: 128, Pages: 261-274, ISSN: 0001-706X

Journal article

Webster BL, Webster JP, Gouvras AN, Garba A, Lamine MS, Diaw OT, Seye MM, Tchuente L-AT, Simoonga C, Mubila L, Mwanga JR, Lwambo NJS, Kabatereine NB, Lange CN, Kariuki C, Mkoji GM, Rollinson D, Stothard JRet al., 2013, DNA 'barcoding' of Schistosoma mansoni across sub-Saharan Africa supports substantial within locality diversity and geographical separation of genotypes, ACTA TROPICA, Vol: 128, Pages: 250-260, ISSN: 0001-706X

Journal article

Webster BL, Diaw OT, Seye MM, Webster JP, Rollinson Det al., 2013, Introgressive Hybridization of Schistosoma haematobium Group Species in Senegal: Species Barrier Break Down between Ruminant and Human Schistosomes, PLoS Neglected Tropical Diseases, Vol: 7, Pages: e2110-e2110

Journal article

Webster BL, Emery AM, Webster JP, Gouvras A, Garba A, Diaw O, Seye MM, Tchuente LAT, Simoonga C, Mwanga J, Lange C, Kariuki C, Mohammed KA, Stothard JR, Rollinson Det al., 2012, Genetic Diversity within Schistosoma haematobium: DNA Barcoding Reveals Two Distinct Groups, PLOS NEGLECTED TROPICAL DISEASES, Vol: 6, ISSN: 1935-2735

Journal article

Webster BL, Littlewood DTJ, 2012, Mitochondrial gene order change in Schistosoma (Platyhelminthes: Digenea: Schistosomatidae), INTERNATIONAL JOURNAL FOR PARASITOLOGY, Vol: 42, Pages: 313-321, ISSN: 0020-7519

Journal article

Norton AJ, Gower CM, Lamberton PHL, Webster BL, Lwambo NJS, Blair L, Fenwick A, Webster JPet al., 2010, Genetic Consequences of Mass Human Chemotherapy for Schistosoma mansoni: Population Structure Pre- and Post-Praziquantel Treatment in Tanzania, AMERICAN JOURNAL OF TROPICAL MEDICINE AND HYGIENE, Vol: 83, Pages: 951-957, ISSN: 0002-9637

Journal article

Webster BL, Rollinson D, Stothard JR, Huyse Tet al., 2010, Rapid diagnostic multiplex PCR (RD-PCR) to discriminate Schistosoma haematobium and S. bovis., J Helminthol, Vol: 84, Pages: 107-114

Schistosoma haematobium and S. bovis are widespread schistosome species causing human and cattle schistosomiasis, respectively, in Africa. The sympatric occurrence of these two species and their ability to infect the same Bulinus intermediate snail hosts necessitates precise methods of identification of the larval stages. A rapid diagnostic 'mulitplex' one-step polymerase chain reaction protocol (RD-PCR) was developed using cytochrome oxidase subunit 1 (COX1) mitochondrial DNA (mtDNA) to discriminate between S. haematobium and S. bovis. A single forward primer and two species-specific reverse primers were used to produce a polymerase chain reaction (PCR) fragment of 306 bp and 543 bp for S. bovis and S. haematobium, respectively. Serial dilutions were carried out on various lifecycle stages and species combinations to test the sensitivity and specificity of the primers. This RD-PCR proved highly sensitive, detecting a single larval stage and as little as 0.78 ng of genomic DNA (gDNA) from an adult schistosome, providing a cost-effective, rapid and robust molecular tool for high-throughput screening of S. haematobium and S. bovis populations. In areas where human and cattle schistosomiasis overlap and are transmitted in close proximity, this mitochondrial assay will be a valuable identification tool for epidemiological studies, especially when used in conjunction with other nuclear diagnostic markers.

Journal article

Webster BL, 2009, Isolation and preservation of schistosome eggs and larvae in RNAlater(R) facilitates genetic profiling of individuals., Parasit Vectors, Vol: 2

Although field-sampling procedures to capture gDNA from individual schistosome larval stages directly from their natural hosts exist, they do pose some technical and logistical challenges hampering certain epidemiological studies. The aim of this study was to develop, refine and evaluate an alternative methodology, which enables better preservation of large numbers of individual schistosome larval stages and eggs collected in low resource endemic areas, to provide PCR-quality DNA for multi-locus genetic analysis. The techniques reported here present simple and effective short-term field and long-term laboratory preservation and storage systems for individually sampled schistosome eggs and larval stages using a commercially available aqueous stabilisation reagent, RNAlater(R) eliminating the need for more cumbersome resources such as refrigerators, heaters and centrifuge equipment for immediate specimen processing. Adaptations to a general gDNA extraction method are described, that enables the acquisition of a gDNA extract (~50 mul), facilitating multiple molecular analyses of each sampled schistosome. The methodology provided PCR-quality mitochondrial and nuclear DNA from laboratory cercariae, miracidia and eggs that had been stored at up to 37 degrees C for 2 weeks and at 4 degrees C for 6 months and also from field collected samples. This present protocol provides significant epidemiological, ethical and practical advantages over existing sampling methods and has the potential to be transferred to studies on other organisms, especially where specimens are unable to be seen by the naked eye, are difficult to handle and need to be obtained from a field environment.

Journal article

Stothard JR, Webster BL, Weber T, Nyakaana S, Webster JP, Kazibwe F, Kabetereine NBet al., 2009, Molecular epidemiology of Schistosoma mansoni in Uganda: DNA barcoding reveals substantive genetic diversity within Lake Albert and Lake Victoria populations., Parasitology, Vol: 136

Journal article

Waeschenbach A, Webster BL, Bray RA, Littlewood DTJet al., 2007, Added resolution among ordinal level relationships of tapeworms (Platyhelminthes: Cestoda) with complete small and large subunit nuclear ribosomal RNA genes., Mol Phylogenet Evol, Vol: 45, Pages: 311-325, ISSN: 1055-7903

The addition of large subunit ribosomal DNA (lsrDNA) to small subunit ribosomal DNA (ssrDNA) has been shown to add resolution to phylogenies at various taxonomic levels for a diversity of phyla. We added nearly complete lsrDNA (4057-4593bp) sequences to ssrDNA (1940-2228bp) for 26 ingroup and 3 outgroup taxa in an attempt to provide an improved ordinal phylogeny for the Cestoda. Ten lsrDNA and seven ssrDNA sequences were generated from new taxa and 13 existing partial lsrDNA sequences were sequenced to completion. The majority of phylogenetic signal in the combined analysis came from lsrDNA (69.6% of parsimonious informative sites, as opposed to 30.4% obtained from ssrDNA), resulting in almost identical topologies for lsrDNA and lsr+ssrDNA (pairwise symmetric distance=6) in model-based analyses. Topology testing found trees based on partial lsrDNA (domains D1-D3)+ssrDNA and complete lsr+ssrDNA to differ significantly; the addition of lsrDNA domains D4-D12 had a significant effect on topology. Overall nodal support was greatest in the combined analysis and weakest for ssrDNA only. Our molecular phylogenies differed significantly from those based on morphology alone. Acetabulate lineages form a monophyletic group, with the Tetraphyllidea being paraphyletic. Support for the combined data was high for the following topology: (Litobothriidea (Lecanicephalidea (Rhinebothrium/Rhodobothrium (Clistobothrium (Pachybothrium(Acanthobothrium Proteocephalidea) (Mesocestoididae, Nippotaeniidea, Cyclophyllidea, Tetrabothriidea)))))); all genus names refer to tetraphyllidean lineages. Although the interrelationships among the four most derived taxa remain uncertain, overall ambiguity of the acetabulate interrelationships was reduced. The Pseudophyllidea were recovered as polyphyletic, with support for a sister-group relationship between Diphyllobothriidae and Haplobothriidea. The monophyly of the Trypanorhyncha was recovered for the first time based on molecular data. The positions

Journal article

Webster BL, Rudolfová J, Horák P, Littlewood DTJet al., 2007, The complete mitochondrial genome of the bird schistosome Trichobilharzia regenti (Platyhelminthes: Digenea), causative agent of cercarial dermatitis., J Parasitol, Vol: 93, Pages: 553-561, ISSN: 0022-3395

The complete mitochondrial (mt) genome of the neuropathogenic bird schistosome Trichobilharzia regenti was fully sequenced in order to develop molecular markers for future diagnostic, molecular ecological, population, and phylogenetic studies. The genome was 14,838 bp in length, with a 68.4% AT bias in protein coding regions. A repeat element (3 x 184 bp) between trnV and trnW distinguished a single short noncoding region. As 9 of 14 genera of schistosomes parasitize birds, future characterization of their mt genomes is desirable for species-specific and strain- or population-specific diagnostic markers; this concerns not only the nasal representatives, e.g., T. regenti characterized in this study, but also numerous species within the predominant group of visceral (blood dwelling) bird schistosomes.

Journal article

Huyse T, Plaisance L, Webster BL, Mo TA, Bakke TA, Bachmann L, Littlewood DTJet al., 2007, The mitochondrial genome of Gyrodactylus salaris (Platyhelminthes: Monogenea), a pathogen of Atlantic salmon (Salmo salar)., Parasitology, Vol: 134, Pages: 739-747, ISSN: 0031-1820

In the present study, we describe the complete mitochondrial (mt) genome of the Atlantic salmon parasite Gyrodactylus salaris, the first for any monogenean species. The circular genome is 14,790 bp in size. All of the 35 genes recognized from other flatworm mitochondrial genomes were identified, and they are transcribed from the same strand. The protein-coding and ribosomal RNA (rRNA) genes share the same gene arrangement as those published previously for neodermatan mt genomes (representing cestodes and digeneans only), and the genome has an overall A+T content of 65%. Three transfer RNA (tRNA) genes overlap with other genes, whereas the secondary structure of 3 tRNA genes lack the DHU arm and 1 tRNA gene lacks the TphiC arm. Eighteen regions of non-coding DNA ranging from 4 to 112 bp in length, totalling 278 bp, were identified as well as 2 large non-coding regions (799 bp and 768 bp) that were almost identical to each other. The completion of the mt genome offers the opportunity of defining new molecular markers for studying evolutionary relationships within and among gyrodactylid species.

Journal article

Gower CM, Shrivastava J, Lamberton PHL, Rollinson D, Webster BL, Emery A, Kabatereine NB, Webster JPet al., 2007, Development and application of an ethically and epidemiologically advantageous assay for the multi-locus microsatellite analysis of Schistosoma mansoni, PARASITOLOGY, Vol: 134, Pages: 523-536, ISSN: 0031-1820

Journal article

Webster BL, Tchuem Tchuenté LA, Southgate VR, 2007, A single-strand conformation polymorphism (SSCP) approach for investigating genetic interactions of Schistosoma haematobium and Schistosoma guineensis in Loum, Cameroon., Parasitol Res, Vol: 100, Pages: 739-745, ISSN: 0932-0113

Single-strand conformation polymorphism (SSCP) analysis of the second internal transcribed spacer (ITS2) of nuclear ribosomal DNA provides a molecular tool for the identification of Schistosoma haematobium, Schistosoma guineensis and the hybrids of these two species. This molecular tool was utilized to provide a detailed analysis of the interactions between S. haematobium and S. guineensis in hybrid zones of Loum, Littoral Province, Cameroon. Individual hybrid schistosomes were identified within the natural populations collected from Loum in 1990, 1999 and 2000, which would have been misidentified as S. haematobium using solely morphological and sequence criteria. This study indicates the complexities of the hybridization between S. haematobium and S. guineensis and emphasizes the importance of assessing morphological, biological and molecular data to gain insights into the interaction of these two species over time.

Journal article

Webster BL, Copley RR, Jenner RA, Mackenzie-Dodds JA, Bourlat SJ, Rota-Stabelli O, Littlewood DTJ, Telford MJet al., 2006, Mitogenomics and phylogenomics reveal priapulid worms as extant models of the ancestral Ecdysozoan., Evol Dev, Vol: 8, Pages: 502-510, ISSN: 1520-541X

Research into arthropod evolution is hampered by the derived nature and rapid evolution of the best-studied out-group: the nematodes. We consider priapulids as an alternative out-group. Priapulids are a small phylum of bottom-dwelling marine worms; their tubular body with spiny proboscis or introvert has changed little over 520 million years and recognizable priapulids are common among exceptionally preserved Cambrian fossils. Using the complete mitochondrial genome and 42 nuclear genes from Priapulus caudatus, we show that priapulids are slowly evolving ecdysozoans; almost all these priapulid genes have evolved more slowly than nematode orthologs and the priapulid mitochondrial gene order may be unchanged since the Cambrian. Considering their primitive bodyplan and embryology and the great conservation of both nuclear and mitochondrial genomes, priapulids may deserve the popular epithet of "living fossil." Their study is likely to yield significant new insights into the early evolution of the Ecdysozoa and the origins of the arthropods and their kin as well as aiding inference of the morphology of ancestral Ecdysozoa and Bilateria and their genomes.

Journal article

Smith AB, Pisani D, Mackenzie-Dodds JA, Stockley B, Webster BL, Littlewood DTJet al., 2006, Testing the molecular clock: molecular and paleontological estimates of divergence times in the Echinoidea (Echinodermata)., Mol Biol Evol, Vol: 23, Pages: 1832-1851, ISSN: 0737-4038

The phylogenetic relationships of 46 echinoids, with representatives from 13 of the 14 ordinal-level clades and about 70% of extant families commonly recognized, have been established from 3 genes (3,226 alignable bases) and 119 morphological characters. Morphological and molecular estimates are similar enough to be considered suboptimal estimates of one another, and the combined data provide a tree that, when calibrated against the fossil record, provides paleontological estimates of divergence times and completeness of their fossil record. The order of branching on the cladogram largely agrees with the stratigraphic order of first occurrences and implies that their fossil record is more than 85% complete at family level and at a resolution of 5-Myr time intervals. Molecular estimates of divergence times derived from applying both molecular clock and relaxed molecular clock models are concordant with estimates based on the fossil record in up to 70% of cases, with most concordant results obtained using Sanderson's semiparametric penalized likelihood method and a logarithmic-penalty function. There are 3 regions of the tree where molecular and fossil estimates of divergence time consistently disagree. Comparison with results obtained when molecular divergence dates are estimated from the combined (morphology + gene) tree suggests that errors in phylogenetic reconstruction explain only one of these. In another region the error most likely lies with the paleontological estimates because taxa in this region are demonstrated to have a very poor fossil record. In the third case, morphological and paleontological evidence is much stronger, and the topology for this part of the molecular tree differs from that derived from the combined data. Here the cause of the mismatch is unclear but could be methodological, arising from marked inequality of molecular rates. Overall, the level of agreement reached between these different data and methodological approaches leads us to be

Journal article

Webster BL, Southgate VR, Littlewood DTJ, 2006, A revision of the interrelationships of Schistosoma including the recently described Schistosoma guineensis., Int J Parasitol, Vol: 36, Pages: 947-955, ISSN: 0020-7519

In light of the recently described human schistosome Schistosoma guineensis and recent phylogenetic studies of the genus Schistosoma, a revision of the interrelationships of the members of this genus is needed. This paper adds to previous phylogenetic studies on the family Schistosomatidae and offers the most up to date and robust phylogeny of the group based on complete small and large nuclear subunit rRNA genes and partial mitochondrial cox1, incorporating most of the 21 species of Schistosoma. Our findings show that the group retains the same topology as that resolved in previous studies except Schistosoma margrebowiei was resolved as the sister taxon to all others in the Schistosoma haematobium species group and S. guineensis was placed as sister species to both Schistosoma bovis and Schistosoma curassoni. The S. haematobium species group contains eight species of which many are of significant medical and veterinary importance. Additionally, many of these species have been shown to hybridise both in the wild and experimentally, making the correct identification and recognition of species very important. A pairwise comparison of cox1 among Schistosoma species suggests this gene alone would fail as a reliable barcode for species identification. Phylogenetic results clearly treat Schistosoma intercalatum and S. guineensis as separate taxa with each more closely related evolutionarily to S. haematobium than to each other. The study also highlights the problems associated with wrongly attributed sequences on public databases such as GenBank.

Journal article

Littlewood DTJ, Lockyer AE, Webster BL, Johnston DA, Le THet al., 2006, The complete mitochondrial genomes of Schistosoma haematobium and Schistosoma spindale and the evolutionary history of mitochondrial genome changes among parasitic flatworms., Mol Phylogenet Evol, Vol: 39, Pages: 452-467, ISSN: 1055-7903

Complete mitochondrial genome sequences for the schistosomes Schistosoma haematobium and Schistosoma. spindale have been characterized. S. haematobium is the causative agent of urinary schistosomiasis in humans and S. spindale uses ruminants as its definitive host; both are transmitted by freshwater snail intermediate hosts. Results confirm a major gene order rearrangement among schistosomes in all traditional Schistosoma species groups other than Schistosoma japonicum; i.e., species groups S. mansoni, S. haematobium, and S. indicum. These data lend support to the 'out of Asia' (East and Southeast Asia) hypothesis for Schistosoma. The gene order change involves translocation of atp6-nad2-trnA and a rearrangement of nad3-nad1 relative to other parasitic flatworm mt genomes so far sequenced. Gene order and tRNA secondary structure changes (loss and acquisition of the DHU and/or TPsiC arms of trnC, trnF, and trnR) between mitochondrial genomes of these and other (digenean and cestode) flatworms were inferred by character mapping onto a phylogeny estimated from nuclear small subunit rRNA gene sequences of these same species, in order to find additional rare genomic changes suitable as synapomorphies. Denser and wider taxon sampling of mt genomes across the Platyhelminthes will validate these putative characters.

Journal article

Webster BL, Tchuem Tchuenté LA, Jourdane J, Southgate VRet al., 2005, The interaction of Schistosoma haematobium and S. guineensis in Cameroon., J Helminthol, Vol: 79, Pages: 193-197, ISSN: 0022-149X

Interactions between schistosomes are complex with some different species being able to mate and hybridize. The epidemiology of schistosomiasis in specific areas of South West Cameroon has evolved remarkably over 30 years as a result of hybridization between Schistosoma guineensis and S. haematobium. Morphological and biological data suggest that S. haematobium replaced S. guineensis in areas of Cameroon through introgressive hybridization. Data are reported on the use of single stranded conformational polymorphism (SSCP) analysis of the nuclear ribosomal second internal transcribed spacer (ITS2) of individual schistosomes from hybrid zones of Cameroon. The data show that since 1990 S. haematobium has completely replaced S. guineensis in Loum, with S. haematobium and the recombinants still present in 2000. This study illustrates the complexities of the dynamics between S. haematobium and S. guineensis in South West Cameroon.

Journal article

Webster BL, Southgate VR, Tchuem Tchuenté L-A, 2003, Isoenzyme analysis of Schistosoma haematobium, S. intercalatum and their hybrids and occurrences of natural hybridization in Cameroon., J Helminthol, Vol: 77, Pages: 269-274, ISSN: 0022-149X

Isoelectric focusing of glucose-6-phosphate dehydrogenase (G6PD) produced clearly identifiable profiles for S. haematobium and S. intercalatum and their hybrids. To provide a more detailed analysis of the interactions of S. haematobium and S. intercalatum in South West Cameroon over the last 12 years, G6PD analyses were carried out on individual schistosomes collected in Kumba in 1990, Loum in 1990, 1999 and 2000 and Barombi Mbo and Barombi Kotto in 1999. Studies were also carried out on the two parental species S. haematobium Barombi Mbo, S. intercalatum Edea and subsequent generations of hybrids resulting from laboratory crosses of the two parental species. The isoenzyme analysis demonstrated that the 1990 isolate from Kumba, was a recombinant of S. intercalatum x S. haematobium, and that 30% of individual schistosomes collected in 1990 in Loum were also recombinants. The remainder gave data indicative of S. haematobium. In 1999, 12.5% of individuals from Loum showed recombination and 10% in 2000. Results from the most recent parasitological survey in October 2000 showed the persistence of the recombinant population in addition to that of S. haematobium. There was also evidence of recombination having taken place in Barombi Kotto but not Barombi Mbo. This study demonstrates how the situation has changed over the last 12 years, and emphasizes the importance of assessing morphological, biological and molecular data together to gain a true picture of the rapidly evolving situation.

Journal article

Webster BL, Southgate VR, 2003, Compatibility of Schistosoma haematobium, S. intercalatum and their hybrids with Bulinus truncatus and B. forskalii., Parasitology, Vol: 127, Pages: 231-242, ISSN: 0031-1820

Schistosoma haematobium and S. intercalatum readily hybridize with each other producing generations of viable hybrid offspring. Experiments were designed to investigate the infectivity and viability of the S. haematobium x S. intercalatum F1 and F2 hybrid larvae in their two intermediate snail hosts compared with the parental species. Analysis of the data obtained suggested that the S. haematobium male x S. intercalatum female F1 hybrid miracidia were more infective to Bulinus truncatus than to B.forskalii, and also more infective to B. truncatus compared with the parental S. haematobium miracidia. This hybrid was also observed to have a greater cercarial productivity from both intermediate hosts and these cercariae were shown to be more infectious and to have a longer longevity compared with the cercariae of S. haematobium, S. intercalatum and the S. haematobium female x S. intercalatum male F1 hybrid cercariae. The S. haematobium female x S. intercalatum male F1 hybrid was shown not to be very successful in all stages of the investigations. The results indicate that the S. haematobium male x S. intercalatum female F1 hybrid may have many reproductive advantages over the reciprocal hybrid and the parental schistosome species. The significance of the results is discussed in relation to the epidemiological consequences occurring in Loum, Cameroon, and other areas where S. haematobium and S. intercalatum are sympatric and able to hybridize.

Journal article

Webster BL, Southgate VR, 2003, Mating interactions of Schistosoma haematobium and S. intercalatum with their hybrid offspring., Parasitology, Vol: 126, Pages: 327-338, ISSN: 0031-1820

Experiments were designed to study the mating behaviour between the Schistosoma haematobium male x S. intercalatumfemale hybrid and the 2 parental species S. haematobium and S. intercalatum. Individual worms were identified by electrophoretic analysis of glucose-6-phosphate dehydrogenase, which was characteristic for each isolate. Analysis of the data obtained showed that both heterospecific and homospecific pairs formed between the hybrids and S. haematobium and S. intercalatum. S. haematobium and the hybrid are better than S. intercalatum in forming pairs, and S. haematobium showed a greater homospecific mate preference compared with the hybrid. Analysis of the data using the Mantel-Haenszel test suggests that mating competition does exist between the schistosomes, with the hybrid being dominant over both the parental species and S. haematobium being dominant over S. intercalatum. The hybrid males showed a greater ability than S. intercalatum and S. haematobium males in taking away S. haematobium and S. intercalatum females from their homospecific males when introduced into a pre-established S. haematobium or S. intercalatum infection. They were able to take females from S. intercalatum homospecific pairs more easily compared with females from S. haematobium homospecific pairs. The significance of the results is discussed in relation to the epidemiological changes of schistosomiasis in Cameroon, where hybridization between S. haematobium and S. intercalatum has taken place, with S. haematobium and the hybrid managing to replace the endemic S. intercalatum over the last 30 years.

Journal article

Southgate V, Tchuem Tchuenté LA, Sène M, De Clercq D, Théron A, Jourdane J, Webster BL, Rollinson D, Gryseels B, Vercruysse Jet al., 2001, Studies on the biology of schistosomiasis with emphasis on the Senegal river basin., Mem Inst Oswaldo Cruz, Vol: 96 Suppl, Pages: 75-78, ISSN: 0074-0276

The construction of the Diama dam on the Senegal river, the Manantali dam on the Bafing river, Mali and the ensuing ecological changes have led to a massive outbreak of Schistosoma mansoni in Northern Senegal, associated with high intensity of infections, due to intense transmission, and the creation of new foci of S. haematobium. Data on the vectorial capacity of Biomphalaria pfeifferi from Ndombo, near Richard Toll, Senegal are presented with sympatric and allopatric (Cameroon) S. mansoni. Comparisons are made on infectivity, cercarial production, chronobiology of cercarial emergence and longevity of infected snails. Recent data on the intermediate host specificity of different isolates of S. haematobium from the Lower and Middle Valley of the Senegal river basin (SRB) demonstrate the existence of at least two strains of S. haematobium. The role of Bulinus truncatus in the transmission of S. haematobium in the Lower and Middle Valleys of the SRB is reviewed. Both S. haematobium and S. mansoni are transmitted in the same foci in some areas of the SRB.

Journal article

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