Schistosoma intercalatum

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J Jourdane - One of the best experts on this subject based on the ideXlab platform.

  • Schistosoma intercalatum an endangered species in cameroon
    Trends in Parasitology, 2003
    Co-Authors: L Tchuem A Tchuente, J Jourdane, Vaughan R Southgate, Bonnie L Webster, Jozef Vercruysse
    Abstract:

    Despite the extremely wide distribution of both intermediate (snail) and definitive hosts, the species Schistosoma intercalatum has a highly restricted distribution in parts of West Africa (Cameroon, Equatorial Guinea, Gabon, Nigeria, Democratic Republic of Congo and Sao Tome). Recent studies showed that the epidemiology of this species is very dynamic, including invasions and extinctions. This article reviews the epidemiology of S. intercalatum in Cameroon, where the species is endangered, and analyses its overall status in Africa. The possible reasons for the limited distribution of S. intercalatum are discussed.

  • a phylogeny based on three mitochondrial genes supports the division of Schistosoma intercalatum into two separate species
    Parasitology, 2003
    Co-Authors: Richard A Kane, L Tchuem A Tchuente, J R Pages, V R Southgate, David Rollinson, D T J Littlewood, Anne E Lockyer, J Jourdane
    Abstract:

    Two recognized strains of Schistosoma iintercalatum, one from the Democratic Republic of Congo (DRC), formerly Zaire, and the other from Cameroon, have been investigated using DNA sequences from 3 mitochondrial genes, cytochrome oxidase subunit 1 (cox1), NADH dehydrogenase subunit 6 (nad6) and the small ribosomal RNA gene (rrnS). In addition, partial DNA sequences from the nuclear large subunit ribosomal RNA gene (lsrDNA) were included within the study. Although partial lsrDNA alone reveals little taxonomic information, phylogenetic analysis of the mitochondrial data demonstrates a clear dichotomy between the 2 purported strains and it is proposed that they should he treated as distinct taxa. The 'original' S. interralatum now falls relatively basal in the S. haematobium group, while the proposed new species is more derived and sister taxon to S. bovis and S. curassoni.

  • a model to explain the replacement of Schistosoma intercalatum by Schistosoma haematobium and the hybrid s intercalatum x s haematobium in areas of sympatry
    Parasitology, 2002
    Co-Authors: Serge Morand, V R Southgate, J Jourdane
    Abstract:

    Numerous hypotheses have been postulated to explain the rapidly changing parasitological situation in Loum, Cameroon as a result of the interaction between Schistosoma haematobium and S. intercalatum. The aim of this study is to test the various hypotheses using a simple mathematical model, incorporating equal and unequal sex ratios of adult schistosomes, recombinations, and levels of compatibility with the intermediate molluscan hosts, B. forskalii and B. truncatus. The model assuming an equal sex ratio does not fit with the existing field data in that it predicts a continued presence of S. intercalatum, S. haematobium and the hybrids. The model assuming a sex bias in favour of males, which reflects the situation usually observed in schistosome populations, predicts the loss S. intercalatum which indeed concurs with the most recent data.

  • experimental evidence of hybrid breakdown between the two geographical strains of Schistosoma intercalatum
    Parasitology, 2002
    Co-Authors: J R Pages, L Tchuem A Tchuente, V R Southgate, J Jourdane
    Abstract:

    Reciprocal crosses (Schistosoma intercalatum male Zaire x S. intercalatum female Cameroon: S. intercalatum female Zaire x S. intercalatum male Cameroon) were produced in 10 mice by exposing each mouse to 60 male cercariae of one isolate and 60 female cercariae of the other isolate, and vice versa. Hybrid generations originating from the two crosses were established. The infectivity of the F 1 , F 2 , F 3 and F 4 hybrid generations were evaluated after exposing snails individually to 5 miracidia. A comparative histological study of snails infected with F 2 and F 4 hybrid sporocysts from both crosses was made to assess abnormalities in the intramolluscan development of the hybrids. The worm recovery rate and fecundity were measured by comparing the fitness of the mid-parents with that of the hybrids. S. intercalatum Cameroon was compatible with Bulinus forskalii and incompatible with B. globosus whereas S. intercalatum Zaire was compatible with B. globosus and incompatible with B. forskalii. In the case of S. intercalatum male Cameroon x S. intercalatum female Zaire, hybrid miracidia develops in both B. forskalii and B. globosus in F 1 , F 2 and F 3 generations. The infection rate was much lower for B. globosus and F 2 and F 3 generations produced few cercariae (less than 30 cercariae in overall per snail) and F 4 miracidia were only infective to B. forskalii again producing few cercariae. At 40 days post-infection the sporocyst contains masses of acidophilic granules originating from the breakup of pycnotic nuclei. Similarly the F 1 , F 2 and F 3 miracidia of the reciprocal cross (S. intercalatum male Zaire x S. intercalatum female Cameroon) exhibited a dual infectivity for B. forskalii and B. globosus, but cercarial productivity was low (less than 30 cercariae overall per snail for F 2 and F 3 generations). Histological studies demonstrated sporocyst degeneration in snails infected with F 4 generation. In the definitive host, the F 1 generation (both crosses) exhibited hybrid vigour in that the worm return was greater than that of the mid-parent, F 2 and F 3 generations. No significant difference in fecundity was demonstrated between the parental strains and the F 1 and F 2 generations, yet egg production of the F 3 generation was significantly lower. It is apparent that there is a post-zygotic barrier in the crosses of S. intercalatum Zaire and S. intercalatum Cameroon from the F 2 generations onwards, and sterility of the F 4 hybrid sporocyst supports the concept of the existence of 2 distinct taxa.

  • polymerase chain reaction assay based on a highly repeated sequence of Schistosoma haematobium a potential tool for monitoring schistosome infested water
    American Journal of Tropical Medicine and Hygiene, 2001
    Co-Authors: Joseph Hamburger, J Jourdane, Reda M R Ramzy, Ibrahim Abbasi, Andreas Ruppel
    Abstract:

    We have cloned from Schistosoma haematobium genome a repeated sequence, the DraI repeated sequence, which consists of tandemly arranged 121-bp-long units and which is highly abundant (approximately 15% of the S. haematobium genome). By these features, the DraI repeat is similar to the Sm1-7 sequence of Schistosoma mansoni previously described by us. However, their nucleotide sequences are profoundly different. Polymerase chain reaction (PCR) primers were designed on the basis of the DraI sequence information and were used in a PCR assay by which as little as 10 fg of Schistosomal DNA as well as individual cercariae were detected. The DraI repeat cross-hybridized with DNA from Schistosoma bovis, Schistosoma magrebowiei, Schistosoma mattheei, Schistosoma curassoni, and Schistosoma intercalatum, but not with DNA from S. mansoni nor from Trichobilharzia ocellata and Echinostoma sp. A potential value of this PCR assay is suggested for monitoring free-living cercariae and infected snails only in bodies free of cross-hybridizing species.

L Tchuem A Tchuente - One of the best experts on this subject based on the ideXlab platform.

  • Schistosoma intercalatum an endangered species in cameroon
    Trends in Parasitology, 2003
    Co-Authors: L Tchuem A Tchuente, J Jourdane, Vaughan R Southgate, Bonnie L Webster, Jozef Vercruysse
    Abstract:

    Despite the extremely wide distribution of both intermediate (snail) and definitive hosts, the species Schistosoma intercalatum has a highly restricted distribution in parts of West Africa (Cameroon, Equatorial Guinea, Gabon, Nigeria, Democratic Republic of Congo and Sao Tome). Recent studies showed that the epidemiology of this species is very dynamic, including invasions and extinctions. This article reviews the epidemiology of S. intercalatum in Cameroon, where the species is endangered, and analyses its overall status in Africa. The possible reasons for the limited distribution of S. intercalatum are discussed.

  • a phylogeny based on three mitochondrial genes supports the division of Schistosoma intercalatum into two separate species
    Parasitology, 2003
    Co-Authors: Richard A Kane, L Tchuem A Tchuente, J R Pages, V R Southgate, David Rollinson, D T J Littlewood, Anne E Lockyer, J Jourdane
    Abstract:

    Two recognized strains of Schistosoma iintercalatum, one from the Democratic Republic of Congo (DRC), formerly Zaire, and the other from Cameroon, have been investigated using DNA sequences from 3 mitochondrial genes, cytochrome oxidase subunit 1 (cox1), NADH dehydrogenase subunit 6 (nad6) and the small ribosomal RNA gene (rrnS). In addition, partial DNA sequences from the nuclear large subunit ribosomal RNA gene (lsrDNA) were included within the study. Although partial lsrDNA alone reveals little taxonomic information, phylogenetic analysis of the mitochondrial data demonstrates a clear dichotomy between the 2 purported strains and it is proposed that they should he treated as distinct taxa. The 'original' S. interralatum now falls relatively basal in the S. haematobium group, while the proposed new species is more derived and sister taxon to S. bovis and S. curassoni.

  • experimental evidence of hybrid breakdown between the two geographical strains of Schistosoma intercalatum
    Parasitology, 2002
    Co-Authors: J R Pages, L Tchuem A Tchuente, V R Southgate, J Jourdane
    Abstract:

    Reciprocal crosses (Schistosoma intercalatum male Zaire x S. intercalatum female Cameroon: S. intercalatum female Zaire x S. intercalatum male Cameroon) were produced in 10 mice by exposing each mouse to 60 male cercariae of one isolate and 60 female cercariae of the other isolate, and vice versa. Hybrid generations originating from the two crosses were established. The infectivity of the F 1 , F 2 , F 3 and F 4 hybrid generations were evaluated after exposing snails individually to 5 miracidia. A comparative histological study of snails infected with F 2 and F 4 hybrid sporocysts from both crosses was made to assess abnormalities in the intramolluscan development of the hybrids. The worm recovery rate and fecundity were measured by comparing the fitness of the mid-parents with that of the hybrids. S. intercalatum Cameroon was compatible with Bulinus forskalii and incompatible with B. globosus whereas S. intercalatum Zaire was compatible with B. globosus and incompatible with B. forskalii. In the case of S. intercalatum male Cameroon x S. intercalatum female Zaire, hybrid miracidia develops in both B. forskalii and B. globosus in F 1 , F 2 and F 3 generations. The infection rate was much lower for B. globosus and F 2 and F 3 generations produced few cercariae (less than 30 cercariae in overall per snail) and F 4 miracidia were only infective to B. forskalii again producing few cercariae. At 40 days post-infection the sporocyst contains masses of acidophilic granules originating from the breakup of pycnotic nuclei. Similarly the F 1 , F 2 and F 3 miracidia of the reciprocal cross (S. intercalatum male Zaire x S. intercalatum female Cameroon) exhibited a dual infectivity for B. forskalii and B. globosus, but cercarial productivity was low (less than 30 cercariae overall per snail for F 2 and F 3 generations). Histological studies demonstrated sporocyst degeneration in snails infected with F 4 generation. In the definitive host, the F 1 generation (both crosses) exhibited hybrid vigour in that the worm return was greater than that of the mid-parent, F 2 and F 3 generations. No significant difference in fecundity was demonstrated between the parental strains and the F 1 and F 2 generations, yet egg production of the F 3 generation was significantly lower. It is apparent that there is a post-zygotic barrier in the crosses of S. intercalatum Zaire and S. intercalatum Cameroon from the F 2 generations onwards, and sterility of the F 4 hybrid sporocyst supports the concept of the existence of 2 distinct taxa.

  • lack of prezygotic isolation by assortative mating between the two cryptic species of the polytypic Schistosoma intercalatum taxon
    Parasitology Research, 2001
    Co-Authors: J R Pages, L Tchuem A Tchuente, V R Southgate, J Jourdane
    Abstract:

    Ten mice were individually exposed to 30 male and 30 female cercariae of Schistosoma intercalatum from Cameroon and to 30 male and 30 female cercariae of S. intercalatum from Zaire. Ten weeks later, the nine surviving mice were killed, and a total of 263 adult schistosomes (228 pairs, 7 unpaired males, 28 unpaired females) were perfused. All worms were identified utilising the random amplified polymorphic DNA technique using primer OPG06 which enables the differentiation of the Cameroon and Zaire genotypes. The data demonstrate that there were no significant differences between the number of homospecific pairs observed compared with the expected number under the null hypothesis. Matings occurred in a random manner indicating that mate choice did not exist for the two genotypes of S. intercalatum. Hence there is no prezygotic isolation mechanism which would prevent the interaction of the two genotypes if they were sympatric. However, as they are allopatric, the possibility of the production of unfit hybrids does not arise. Consequently, the reinforcement of a prezygotic isolating mechanism does not play a significant role in the speciation process.

  • molecular arguments for splitting of Schistosoma intercalatum into two distinct species
    Parasitology Research, 2001
    Co-Authors: J R Pages, L Tchuem A Tchuente, Vaughan R Southgate, Patrick Durand, J Jourdane
    Abstract:

    The taxonomic status of the two known strains of Schistosoma intercalatum, the Lower Guinea strain (originating from Edea, Cameroon) and the Zaire strain (originating from Kinshasa, Democratic Republic of Congo, formerly Zaire) was examined using random amplified polymorphic DNA (RAPD) markers. Two additional species within the S. haematobium group, S. haematobium and S. mattheei, were included in the study. DNA was extracted from four male and four female worms of each species and strain under investigation. In all, 13 primers gave reproducible and informative marker patterns; the monomorphic bands in all the males and females of each sample were scored, and 138 bands were included in the final analysis. Overall, 14 RAPD fragments were shared by all the schistosomes studied, and 19 RAPD fragments were considered to be sex markers. Only 22% (20/91) of the RAPD fragments were shared between S. intercalatum Zaire and S. intercalatum Cameroon. The mean values recorded for the Nei and Li's genetic distances between S. haematobium and S. mattheei and between S. intercalatum Zaire and S. intercalatum Cameroon were 0.546 and 0.596, respectively. A principal component analysis and one-way analysis of variance (ANOVA/MANOVA) showed a significant separation between S. intercalatum Zaire and S. intercalatum Cameroon. The data support the hypothesis that S. intercalatum Zaire and S. intercalatum Cameroon are distinct species. Additional molecular-biology studies are in progress that involve the use of nuclear and mitochondrial markers to confirm the extent of the genetic divergence prior to the establishment of final decision on the taxonomic status of the two strains of S. intercalatum.

Vaughan R Southgate - One of the best experts on this subject based on the ideXlab platform.

  • Recent Studies on Schistosoma intercalatum: Taxonomic Status, Puzzling Distribution and Transmission Foci Revisited
    2014
    Co-Authors: Joseph Jourdane, Vaughan R Southgate, Jean René Pagès, Patrick Dur, Louis Albert, Tchuem Tchuenté
    Abstract:

    Schistosoma intercalatum, which causes human rectal schistosomiasis in Africa, still presents a great interest for its imprecise taxonomic status and its puzzling distribution in Africa. Two geographically isolated strains of S. intercalatum are recognized, the Lower Guinea strain and the Congo strain, which differ from each other in a number of morphological, biological and biochemical characteristics. Recent molecular data using RAPD markers indicate high divergence between the two strains, with values of Nei and Li’s similarity indice allowing recognition of two genetically distinct taxa: experiments on pre- and post-isolating mechanisms are in progress in order to re-evaluate the taxonomic status of this polytypic species. With regard to its geographical distribution, S. intercalatum is characterized by the existence of two stable endemic areas (localized in Lower Guinea and North East of Democratic Republic of Congo) which correspond to the historical areas of species discovery, and the emergence during the last 15 years of new foci of the Lower Guinea strain outside previously known endemic areas. The absence of local adaptation of the Lower Guinea strain to its intermediate host, supported by experimental studies, may help to facilitate the spread of this strain. Nevertheless, the present restricted distribution of this species remains puzzling, because its potential snail hosts (bulinids) are widely distributed throughout much of Africa. Recent experimental and epidemiological studie

  • Schistosoma intercalatum an endangered species in cameroon
    Trends in Parasitology, 2003
    Co-Authors: L Tchuem A Tchuente, J Jourdane, Vaughan R Southgate, Bonnie L Webster, Jozef Vercruysse
    Abstract:

    Despite the extremely wide distribution of both intermediate (snail) and definitive hosts, the species Schistosoma intercalatum has a highly restricted distribution in parts of West Africa (Cameroon, Equatorial Guinea, Gabon, Nigeria, Democratic Republic of Congo and Sao Tome). Recent studies showed that the epidemiology of this species is very dynamic, including invasions and extinctions. This article reviews the epidemiology of S. intercalatum in Cameroon, where the species is endangered, and analyses its overall status in Africa. The possible reasons for the limited distribution of S. intercalatum are discussed.

  • molecular arguments for splitting of Schistosoma intercalatum into two distinct species
    Parasitology Research, 2001
    Co-Authors: J R Pages, L Tchuem A Tchuente, Vaughan R Southgate, Patrick Durand, J Jourdane
    Abstract:

    The taxonomic status of the two known strains of Schistosoma intercalatum, the Lower Guinea strain (originating from Edea, Cameroon) and the Zaire strain (originating from Kinshasa, Democratic Republic of Congo, formerly Zaire) was examined using random amplified polymorphic DNA (RAPD) markers. Two additional species within the S. haematobium group, S. haematobium and S. mattheei, were included in the study. DNA was extracted from four male and four female worms of each species and strain under investigation. In all, 13 primers gave reproducible and informative marker patterns; the monomorphic bands in all the males and females of each sample were scored, and 138 bands were included in the final analysis. Overall, 14 RAPD fragments were shared by all the schistosomes studied, and 19 RAPD fragments were considered to be sex markers. Only 22% (20/91) of the RAPD fragments were shared between S. intercalatum Zaire and S. intercalatum Cameroon. The mean values recorded for the Nei and Li's genetic distances between S. haematobium and S. mattheei and between S. intercalatum Zaire and S. intercalatum Cameroon were 0.546 and 0.596, respectively. A principal component analysis and one-way analysis of variance (ANOVA/MANOVA) showed a significant separation between S. intercalatum Zaire and S. intercalatum Cameroon. The data support the hypothesis that S. intercalatum Zaire and S. intercalatum Cameroon are distinct species. Additional molecular-biology studies are in progress that involve the use of nuclear and mitochondrial markers to confirm the extent of the genetic divergence prior to the establishment of final decision on the taxonomic status of the two strains of S. intercalatum.

  • recent studies on Schistosoma intercalatum taxonomic status puzzling distribution and transmission foci revisited
    Memorias Do Instituto Oswaldo Cruz, 2001
    Co-Authors: J Jourdane, Vaughan R Southgate, J R Pages, Patrick Durand, L Tchuem A Tchuente
    Abstract:

    Schistosoma intercalatum, which causes human rectal schistosomiasis in Africa, still presents a great interest for its imprecise taxonomic status and its puzzling distribution in Africa. Two geographically isolated strains of S. intercalatum are recognized, the Lower Guinea strain and the Congo strain, which differ from each other in a number of morphological, biological and biochemical characteristics. Recent molecular data using RAPD markers indicate high divergence between the two strains, with values of Nei and Li's similarity index allowing recognition of two genetically distinct taxa: experiments on pre- and post-isolating mechanisms are in progress in order to re-evaluate the taxonomic status of this polytypic species. With regard to its geographical distribution, S. intercalatum is characterized by the existence of two stable endemic areas (localized in Lower Guinea and North East of Democratic Republic of Congo) which correspond to the historical areas of species discovery, and the emergence during the last 15 years of new foci of the Lower Guinea strain outside previously known endemic areas. The absence of local adaptation of the Lower Guinea strain to its intermediate host, supported by experimental studies, may help to facilitate the spread of this strain. Nevertheless, the present restricted distribution of this species remains puzzling, because its potential snail hosts (bulinids) are widely distributed throughout much of Africa. Recent experimental and epidemiological studies suggest that interspecific sexual interactions between human schistosomes could have a role in limiting the distribution of S. intercalatum: the competitive sexual processes acting among human schistosomes show that S. haematobium and S. mansoni are always competitively dominant over S. intercalatum. These epidemiological observations lead the authors to distinguish three kinds of transmission foci for S. intercalatum.

  • evidence for the occurrence of Schistosoma intercalatum at albert nile in northern uganda
    American Journal of Tropical Medicine and Hygiene, 1994
    Co-Authors: E I Odongoaginya, Vaughan R Southgate, Andreas Mueller, Tom Loronilakwo, Christopher M Ndugwa, Ulrich Schweigmann, Hanns M Seitz, Ekkehard Doehringschwerdtfeger
    Abstract:

    During a field investigation in Rhino Camp at Albert Nile in northern Uganda, 77.8% of 636 persons excreted Schistosoma mansoni ova that were detected by the Kato-Katz method. Six patients, 8-17 years of age, had terminally spined schistosome eggs in their stools. These findings were confirmed when preserved specimens were examined at the Institute of Medical Parasitology in Bonn using a concentration technique. The mean +/- SD length of 36 terminally spined eggs was 156 +/- 6 microns and the mean +/- SD width was 59 +/- 3.6 microns. Urine filtration in the study patients revealed no schistosome eggs in the urine. It is concluded that these findings provide evidence for the occurrence of S. intercalatum at Albert Nile in northern Uganda.

J R Pages - One of the best experts on this subject based on the ideXlab platform.

  • a phylogeny based on three mitochondrial genes supports the division of Schistosoma intercalatum into two separate species
    Parasitology, 2003
    Co-Authors: Richard A Kane, L Tchuem A Tchuente, J R Pages, V R Southgate, David Rollinson, D T J Littlewood, Anne E Lockyer, J Jourdane
    Abstract:

    Two recognized strains of Schistosoma iintercalatum, one from the Democratic Republic of Congo (DRC), formerly Zaire, and the other from Cameroon, have been investigated using DNA sequences from 3 mitochondrial genes, cytochrome oxidase subunit 1 (cox1), NADH dehydrogenase subunit 6 (nad6) and the small ribosomal RNA gene (rrnS). In addition, partial DNA sequences from the nuclear large subunit ribosomal RNA gene (lsrDNA) were included within the study. Although partial lsrDNA alone reveals little taxonomic information, phylogenetic analysis of the mitochondrial data demonstrates a clear dichotomy between the 2 purported strains and it is proposed that they should he treated as distinct taxa. The 'original' S. interralatum now falls relatively basal in the S. haematobium group, while the proposed new species is more derived and sister taxon to S. bovis and S. curassoni.

  • experimental evidence of hybrid breakdown between the two geographical strains of Schistosoma intercalatum
    Parasitology, 2002
    Co-Authors: J R Pages, L Tchuem A Tchuente, V R Southgate, J Jourdane
    Abstract:

    Reciprocal crosses (Schistosoma intercalatum male Zaire x S. intercalatum female Cameroon: S. intercalatum female Zaire x S. intercalatum male Cameroon) were produced in 10 mice by exposing each mouse to 60 male cercariae of one isolate and 60 female cercariae of the other isolate, and vice versa. Hybrid generations originating from the two crosses were established. The infectivity of the F 1 , F 2 , F 3 and F 4 hybrid generations were evaluated after exposing snails individually to 5 miracidia. A comparative histological study of snails infected with F 2 and F 4 hybrid sporocysts from both crosses was made to assess abnormalities in the intramolluscan development of the hybrids. The worm recovery rate and fecundity were measured by comparing the fitness of the mid-parents with that of the hybrids. S. intercalatum Cameroon was compatible with Bulinus forskalii and incompatible with B. globosus whereas S. intercalatum Zaire was compatible with B. globosus and incompatible with B. forskalii. In the case of S. intercalatum male Cameroon x S. intercalatum female Zaire, hybrid miracidia develops in both B. forskalii and B. globosus in F 1 , F 2 and F 3 generations. The infection rate was much lower for B. globosus and F 2 and F 3 generations produced few cercariae (less than 30 cercariae in overall per snail) and F 4 miracidia were only infective to B. forskalii again producing few cercariae. At 40 days post-infection the sporocyst contains masses of acidophilic granules originating from the breakup of pycnotic nuclei. Similarly the F 1 , F 2 and F 3 miracidia of the reciprocal cross (S. intercalatum male Zaire x S. intercalatum female Cameroon) exhibited a dual infectivity for B. forskalii and B. globosus, but cercarial productivity was low (less than 30 cercariae overall per snail for F 2 and F 3 generations). Histological studies demonstrated sporocyst degeneration in snails infected with F 4 generation. In the definitive host, the F 1 generation (both crosses) exhibited hybrid vigour in that the worm return was greater than that of the mid-parent, F 2 and F 3 generations. No significant difference in fecundity was demonstrated between the parental strains and the F 1 and F 2 generations, yet egg production of the F 3 generation was significantly lower. It is apparent that there is a post-zygotic barrier in the crosses of S. intercalatum Zaire and S. intercalatum Cameroon from the F 2 generations onwards, and sterility of the F 4 hybrid sporocyst supports the concept of the existence of 2 distinct taxa.

  • lack of prezygotic isolation by assortative mating between the two cryptic species of the polytypic Schistosoma intercalatum taxon
    Parasitology Research, 2001
    Co-Authors: J R Pages, L Tchuem A Tchuente, V R Southgate, J Jourdane
    Abstract:

    Ten mice were individually exposed to 30 male and 30 female cercariae of Schistosoma intercalatum from Cameroon and to 30 male and 30 female cercariae of S. intercalatum from Zaire. Ten weeks later, the nine surviving mice were killed, and a total of 263 adult schistosomes (228 pairs, 7 unpaired males, 28 unpaired females) were perfused. All worms were identified utilising the random amplified polymorphic DNA technique using primer OPG06 which enables the differentiation of the Cameroon and Zaire genotypes. The data demonstrate that there were no significant differences between the number of homospecific pairs observed compared with the expected number under the null hypothesis. Matings occurred in a random manner indicating that mate choice did not exist for the two genotypes of S. intercalatum. Hence there is no prezygotic isolation mechanism which would prevent the interaction of the two genotypes if they were sympatric. However, as they are allopatric, the possibility of the production of unfit hybrids does not arise. Consequently, the reinforcement of a prezygotic isolating mechanism does not play a significant role in the speciation process.

  • molecular arguments for splitting of Schistosoma intercalatum into two distinct species
    Parasitology Research, 2001
    Co-Authors: J R Pages, L Tchuem A Tchuente, Vaughan R Southgate, Patrick Durand, J Jourdane
    Abstract:

    The taxonomic status of the two known strains of Schistosoma intercalatum, the Lower Guinea strain (originating from Edea, Cameroon) and the Zaire strain (originating from Kinshasa, Democratic Republic of Congo, formerly Zaire) was examined using random amplified polymorphic DNA (RAPD) markers. Two additional species within the S. haematobium group, S. haematobium and S. mattheei, were included in the study. DNA was extracted from four male and four female worms of each species and strain under investigation. In all, 13 primers gave reproducible and informative marker patterns; the monomorphic bands in all the males and females of each sample were scored, and 138 bands were included in the final analysis. Overall, 14 RAPD fragments were shared by all the schistosomes studied, and 19 RAPD fragments were considered to be sex markers. Only 22% (20/91) of the RAPD fragments were shared between S. intercalatum Zaire and S. intercalatum Cameroon. The mean values recorded for the Nei and Li's genetic distances between S. haematobium and S. mattheei and between S. intercalatum Zaire and S. intercalatum Cameroon were 0.546 and 0.596, respectively. A principal component analysis and one-way analysis of variance (ANOVA/MANOVA) showed a significant separation between S. intercalatum Zaire and S. intercalatum Cameroon. The data support the hypothesis that S. intercalatum Zaire and S. intercalatum Cameroon are distinct species. Additional molecular-biology studies are in progress that involve the use of nuclear and mitochondrial markers to confirm the extent of the genetic divergence prior to the establishment of final decision on the taxonomic status of the two strains of S. intercalatum.

  • recent studies on Schistosoma intercalatum taxonomic status puzzling distribution and transmission foci revisited
    Memorias Do Instituto Oswaldo Cruz, 2001
    Co-Authors: J Jourdane, Vaughan R Southgate, J R Pages, Patrick Durand, L Tchuem A Tchuente
    Abstract:

    Schistosoma intercalatum, which causes human rectal schistosomiasis in Africa, still presents a great interest for its imprecise taxonomic status and its puzzling distribution in Africa. Two geographically isolated strains of S. intercalatum are recognized, the Lower Guinea strain and the Congo strain, which differ from each other in a number of morphological, biological and biochemical characteristics. Recent molecular data using RAPD markers indicate high divergence between the two strains, with values of Nei and Li's similarity index allowing recognition of two genetically distinct taxa: experiments on pre- and post-isolating mechanisms are in progress in order to re-evaluate the taxonomic status of this polytypic species. With regard to its geographical distribution, S. intercalatum is characterized by the existence of two stable endemic areas (localized in Lower Guinea and North East of Democratic Republic of Congo) which correspond to the historical areas of species discovery, and the emergence during the last 15 years of new foci of the Lower Guinea strain outside previously known endemic areas. The absence of local adaptation of the Lower Guinea strain to its intermediate host, supported by experimental studies, may help to facilitate the spread of this strain. Nevertheless, the present restricted distribution of this species remains puzzling, because its potential snail hosts (bulinids) are widely distributed throughout much of Africa. Recent experimental and epidemiological studies suggest that interspecific sexual interactions between human schistosomes could have a role in limiting the distribution of S. intercalatum: the competitive sexual processes acting among human schistosomes show that S. haematobium and S. mansoni are always competitively dominant over S. intercalatum. These epidemiological observations lead the authors to distinguish three kinds of transmission foci for S. intercalatum.

Andreas Ruppel - One of the best experts on this subject based on the ideXlab platform.

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