Biomedical subjects

R Touassem

Publications and source records attributed to R Touassem.

10 recordsLinked to original sources

PubMed1996

A simple computer-assisted method to identify schistosome cercariae.

Several methods have been suggested to identify schistosome cercariae. In the present work, a new method is proposed, based on the analysis of the distribution of sensory endings (sensillae) on the body of the cercariae, revealed by an impregnation with silver nitrate. We determined the mutual distances between the sensillae and calculated the mean values, standard deviations, coefficients of asymmetry, and of kurtosis of the distribution of these mutual distances. Applied to two species, Schistosoma mansoni from Brazil and S. intercalatum from Cameroon, these mutual distances had the same mean value and the same standard deviation but quite different coefficients of symmetry (0.34 +/- 0.11 versus 0.73 +/- 0.08; P < 0.0001) and of kurtosis (-0.82 +/- 0.27 versus -0.58 +/- 0.31; P < 0.0001). The latter two indices were therefore very effective for discriminating the two species. The present method can be applied to other species and to hybrids in the field.

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PubMed1992

Identification of Schistosoma mansoni, S. rodhaini, S. bovis, S. haematobium, and S. intercalatum cercariae using segmentation analysis.

Cercariae of five species of schistosomes identified with certainty were fixed in boiled alcohol and mounted in glycerol-alcohol mixture. The cercarian body (Cbl) and tail-furcae lengths (Ctl) were measured, the values of which were treated using a computer. Even mean values allowed partly identification of the present species, the segmentation analysis gave better informations for separating any cercaria taken at random, with a given probability (p). Thus, five classes (A, B, C, D, E) have been established: class A: Cbl > 139 microns and Ctl, > 236 microns, p = 0.59 to be considered as S. bovis; class B: Cbl > 139 and Ctl < 236, p = 0.86 to be considered as S. haematobium; class C; Cbl < 114 microns, p = 0.75 to be considered as S. intercalatum; class D: 114 < Cbl < 125 microns, p = 0.57 to be considered as S. mansoni; class E: 125 < Cbl < 139 microns, p = 0.57 to be considered as S. rodhaini. Two groups of schistosome have been established on basis of cercarian morphometry with S. intercalatum, S. mansoni and S. rodhaini from one side, S. haematobium and S. bovis to the other side.

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PubMed1989

Can tegumental morphology be used as a taxonomic criterion between Schistosoma haematobium, S. intercalatum, and S. bovis?

A comparative study of the evolution in time of the tegumental morphology of male adult Schistosoma haematobium from Niger, S. intercalatum from Cameroon and Zaire, and S. bovis from Spain and Sudan was carried out with scanning electron microscopy. Interindividual, interstrain, and interspecies variations are pointed out. The value of the morphological criterion (tegument with or without spines) is discussed. The tegumental morphology can be used for the identification of schistosome species showing strong phyletic affinities under precise experimental conditions. In the present work, this criterion permits the characterization of strains of S. bovis from Sudan and Spain.

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PubMed1989

Schistosoma rodhaini: intramolluscan larval development, migration and replication processes of daughter sporocysts.

The larval development of Schistosoma rodhaini in Biomphalaria glabrata presents two features of interest. The first concerns the migration of daughter sporocysts: only a fraction of the daughter sporocysts produced by the mother sporocyst migrate directly towards the digestive gland of the snail and become cercariogenous; the others remain in the anterior region of the snail where the majority transforms into small sporocystogenous sporocysts. The second point concerns the replication processes: only direct replication of daughter sporocysts was observed in sporocysts in a prehepatic localization. The demographic processes involved in the development of S. rodhaini are compared with other species of Schistosoma and interpreted as an adaptive character for better exploitation of the snail host.

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PubMed1989

Schistosoma rodhaini: dynamics and cercarial production for mono- and pluri-miracidial infections of Biomphalaria glabrata.

No significant difference in cercarial production was noted when Biomphalaria glabrata from Brazil were exposed to one or several miracidia of Schistosoma rodhaini from Burundi, even though the dynamics seemed different. The minor differences can be explained by the intramolluscal larval development of this parasite characterized by the production of a high number of daughter sporocysts over a long period.

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PubMed1987

Egg polymorphism of Schistosoma bovis.

A study of the egg morphology of Schistosoma bovis from Sudan and Spain revealed some differences in the size and shape of eggs depending on the method of their sampling. The size of eggs (especially the length) tended to increase in the following order: those recovered from the worm uterus smaller than those recovered from the liver and from the faeces of mice for both strains. The shape of eggs from the host faeces (the typical ones) and from the distal portion of the worm uterus for both strains tended to be homogeneous whereas those from the host liver were more heterogeneous. A comparison between the eggs of the two strains showed a great similarity in spite of their distant geographical origins; only the length of the eggs collected from the distal part of the worm uterus and those from the host faeces showed a significant difference at a 99% confidence limit.

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PubMed1986

Comparative analysis of the Schistosoma mansoni and Schistosoma bovis cercarial production under the influence of praziquantel.

Snails infected with Schistosoma mansoni and S. bovis and fed with a food-Praziquantel mixture stop shedding cercariae for several days. The cercarial production restarts at different levels after stopping treatment: for some Biomphalaria glabrata, the restarting phase of production reaches a high level whereas for other B. glabrata and all of the P. metidjensis, the level of production remains low. Histological studies revealed that at the exact moment of this treatment, there is a total destruction of many nearly mature cercariae whereas the young cercarial embryos and the tegument of the sporocyst remain unharmed. When treatment stops, there is a pronounced proliferation of third-generation sporocysts (Sp III) which invade the available space of the snails' digestive gland.

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PubMed1986

Study on the intramolluscal development of Schistosoma bovis: demonstration of three patterns of sporocystogenesis by daughter sporocysts.

Daughter sporocysts (SpII) of Schistosoma bovis produced by the mother sporocyst (SpI) can direct their production along three different pathways during intramolluscal development. (i) direct sporocystogenesis--tertiary sporocysts (SpIII) are directly produced by non-cercariae producing daughter sporocysts (SpII). (ii) Simultaneous sporocystogenesis and cercariogenesis--SpIII are produced by SpII in which cercariae are being produced. (iii) Sporocystogenesis after cercariogenesis--SpIII are produced by SpII in which cercariae are undergoing degeneration. These mechanisms can be interpreted in terms of demographic strategy leading swiftly to the taking over and optimum exploitation of the host's biotic capacity.

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PubMed1985

[The choice of intermediate molluscan host by the miracidium of Schistosoma bovis].

When the usual intermediate hosts (B. truncatus and P. metidjensis) and several other species of Molluscs are together exposed to the miracidia of S. bovis, we demonstrate that about 75% of the miracidia penetrate B. truncatus and P. metidjensis, while 25% penetrate the Pulmonates (B. glabrata, B. straminea and H. duryi) and no miracidium penetrates the Prosobranches (M. tuberculata, M. cornuarietis). When the miracidia penetrate the non-vector Molluscs, it takes less than 24 hours for them to get encapsulated, except for B. straminea, in which the reaction takes 24 to 48 hours.

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PubMed1984

[Development of the sporocysts of Schistosoma bovis after microsurgical transplantation in Bulinus truncatus].

Microsurgical transplantations of Schistosoma bovis daughter sporocysts to uninfected Bulinus truncatus leads to a dedifferenciation of transplanted sporocysts producing an additional generation of daughter sporocysts. These ones settle into the whole digestive gland and produce infective cercariae. For all the parasitosis, a part of the daughter sporocysts born from the transplanted ones, remains in the head-foot region and are in their turn responsible for an active sporocystogeny. Data demonstrate that the cercarial production dynamics is at least in part in relation with the intramollusc dynamics of sporocyst populations. Success of microsurgical transplantation of S. bovis sporocysts permits cloning perspective of this species.

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