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B Oury

Publications and source records attributed to B Oury.

11 recordsLinked to original sources
PubMed2001

Evidence for clonal propagation in natural isolates of Plasmodium falciparum from Venezuela.

We have analyzed 75 isolates of Plasmodium falciparum, collected in Venezuela during both the dry (November) and rainy (May-July) seasons, with a range of genetic markers including antigen genes and 14 random amplified polymorphic DNA (RAPD) primers. Thirteen P. falciparum stocks from Kenya and four other Plasmodium species are included in the analysis for comparison. Cross-hybridization shows that the 14 RAPD primers reveal 14 separate regions of the parasite's genome. The P. falciparum isolates are a monophyletic clade, significantly different from the other Plasmodium species. We identify three RAPD characters that could be useful as "tags" for rapid species identification. The Venezuelan genotypes fall into two discrete genetic subdivisions associated with either the dry or the rainy season; the isolates collected in the rainy season exhibit greater genetic diversity. There is significant linkage disequilibrium in each seasonal subsample and in the full sample. In contrast, no linkage disequilibrium is detected in the African sample. These results support the hypothesis that the population structure of P. falciparum in Venezuela, but not in Africa, is predominantly clonal. However, the impact of genetic recombination on Venezuelan P. falciparum seems higher than in parasitic species with long-term clonal evolution like Trypanosoma cruzi, the agent of Chagas' disease. The genetic structure of the Venezuelan samples is similar to that of Escherichia coli, a bacterium that propagates clonally, with occasional genetic recombination.

Animals↗
PubMed1999

Plasmodium falciparum: population genetic analysis by multilocus enzyme electrophoresis and other molecular markers.

Abderrazak, S. B., Oury, B, Lal, A. A., Bosseno, M.-F., Force-Barge, P., Dujardin, J.-P., Fandeur, T., Molez, J.-F., Kjellberg, F., Ayala, F. J., and Tibayrenc, M. 1999. Plasmodium falciparum: Population genetic analysis by multilocus enzyme electrophoresis and other molecular markers. Experimental Parasitology 92, 232-238. The population structure of Plasmodium falciparum, the agent of malignant malaria, is uncertain. We have analyzed multilocus enzyme electrophoresis (MLEE) polymorphisms at 7-12 gene loci in each of four populations (two populations in Burkina Faso, one in Sudan, one in Congo), plus one "cosmopolitan" sample consisting of parasite cultures from 15 distant localities in four different continents. We have also performed random amplified polymorphic DNA analysis (RAPD) and restriction fragment length polymorphism (RFLP) and characterized gene varia tion at four antigen genes in the Congo population. All genetic assays show abundant genetic variability in all populations analyzed. With the isoenzyme assays, strong linkage disequilibrium is apparent in at least two local populations, the Congo population and one population from Burkina Faso, as well as in the cosmopolitan sample, and less definitely in the other Burkina Faso population. However, no linkage disequilibrium is detected in the Congo population with the molecular assays. We failed to detect any nonrandom association between the different kinds of genetic markers; that is, MLEE with RAPD or RFLP, RAPD with RFLP, and so on. Although isoenzyme data show statistical departures from panmictic expectations, these results suggest that in the areas under survey, P. falciparum populations do not undergo predominant clonal evolution and show no clear-cut subdivisions, un like Trypanosoma cruzi, Leishmania sp., and other major parasitic species. We discuss the epidemiological and taxonomical significance of these results.

Animals↗
PubMed1998

Trypanosoma cruzi: impact of clonal evolution of the parasite on its biological and medical properties.

Trypanosoma cruzi populations are subdivided into natural clones that can exhibit considerable genetic differences. It has been proposed that T. cruzi clonal structure has a major impact on this parasite's biological properties. The present work aims at testing this hypothesis. Twenty-one stocks isolated from various ecological cycles, places, and hosts were characterized by multilocus enzyme electrophoresis (MLEE) with 22 genetic loci and random amplification of polymorphic DNA (RAPD) with 10 primers on the one hand and by 14 different biological parameters on the other hand. These parameters were related to: (i) growth kinetics of epimastigotes and amastigotes; (ii) infection of culture cells by amastigotes; (iii) viability of extracellular trypomastigotes; or (iv) sensitivity of epimastigotes, trypomastigotes, and amastigotes to Benznidazole and Nifurtimox. MLEE and RAPD results exhibited parity to each other, as previously noted (M. Tibayrenc, K. Neubauer, C. Barnabé, F. Guerrini, D. Skarecky, and F. J. Ayala, 1993, Proceedings of the National Academy of Sciences of the USA 90, 1335-1339), and showed that the 21 stocks were distributed into three main genetic groups, 19/20, 32, and 39, corresponding to the major clones 19, 20, 32, and 39 previously described on the basis of 15 isozyme loci. Most biological parameters showed a strong correlation to the genetic distances evaluated from either MLEE or RAPD, which favors the working hypothesis. The only exception came from drug sensitivity estimated on trypomastigote forms. The overall results made it possible to firmly reject the null hypothesis that there is no relationships between evolutionary distances and biological differences in T. cruzi natural clones.

Animals↗
PubMed1997

Assessment of exposure to carcinogenic N-nitrosamines in the rubber industry.

Exposures to volatile nitrosamines were measured at 24 rubber manufacturing plants from 1992 to 1995. A total of 709 exposure measurements were taken in general areas or personal breathing zones to estimate exposure according to production types (seals, joints, tyres, gloves, etc.) and production steps, from mixing to storage. Five different nitrosamines were identified. N-Nitrosodimethylamine is the most frequently encountered nitrosamine and represents the most important fraction of the total nitrosamine concentration measured in a given sample. This fact is consistent with the use of rubber additives containing corresponding amine precursors. One hundred and forty-one of the 709 values exceeded the German target value (TRK) of 2.5 micrograms/m3 for all nitrosamines present from rubber vulcanisation, the only available standard for occupational nitrosamine exposures. The salt bath curing process generates particularly high nitrosamine levels, 90% of the 96 measurements being over the TRK, with many values exceeding 20 micrograms/m3. The reasons why the TRK is exceeded are generally well identified. To reduce nitrosamine emission levels it would be advisable to eliminate nitrogen oxide sources, principally by using a process other than salt bath curing, and to develop different rubber stocks that do not contain secondary aliphatic amine functional groups ("safe amines").

Adult↗
PubMed1997

Trypanosoma cruzi: evaluation of a RAPD synapomorphic fragment as a species-specific DNA probe.

A methodological approach is proposed to select rapidly DNA sequences characterized by a well defined specificity and potentially interesting to be used as diagnostic probes or as taxonomic and phylogenetic markers. A fragment amplified from a diversified sample of Trypanosoma cruzi stocks by the RAPD (random amplified polymorphic DNA) method with the A8 primer, previously found to be monomorphic in all stocks, was separated in 2 fragments using polyacrylamide electrophoresis. RFLP (restriction fragment length polymorphism) analysis of the 750-bp fragment common to all stocks revealed some sequence heterogeneity within the T. cruzi species, whereas hybridization experiments showed a high homology between fragments amplified from different T. cruzi stocks. These results suggest that sequence analysis will allow the design of internal primers to be used as probes to target specific taxonomic levels (clone, family of related clones, or species) and for diagnosis.

Animals↗
PubMed1992

Relationships between circulating S-antigens, naturally acquired antibodies to Plasmodium falciparum exoantigens and malaria attack in a mesoendemic area.

A survey involving 77 individuals living in two savannah villages near Bobo Dioulasso (Burkina Faso, West Africa), was performed in June 1987 (before), August-September (during) and January 1988 after the seasonal transmission. The clinical longitudinal study during the seasonal period permitted us to define three different groups in terms of both age and occurrence of malaria attack (MA; greater than or equal to 5000 parasites/mm3 of blood and axillary fever greater than or equal to 37.8 degrees C). The presence of circulating stable antigen (S-Ag) and the antibody responses against exoantigens (E-Ag) of Plasmodium falciparum were also evaluated at three observations periods: beginning, during and after the transmission season. The adult group (III) had the highest rates of IgG Ab to E-Ag although, IgM prevalence to E-Ag was maximal in the group II (individuals with no malaria attack and age less than or equal to 15 years old). Group I (persons with less than or equal to 15 years old and who contracted at least one MA) did not have any S-Ag at the first observation period and showed the lowest rate of antibodies to E-Ag. The probability of occurrence of an MA calculated from these parameters at the beginning of the transmission period were correct in 78.9% of the cases in children (Groups I & II) and in 71.8% of adults during the subsequent transmission period. Therefore these values could be used for evaluating the probability of occurrence of a clinical MA during the transmission period in a mesoendemic area. S-Ag and antibodies to E-Ag could participate positively in the mechanisms involved in the development of the immune status.

Adolescent↗
PubMed1991

Are eukaryotic microorganisms clonal or sexual? A population genetics vantage.

We argue that the mode of reproduction of microorganisms in nature can only be decided by population genetic information. The evidence available indicates that many parasitic protozoa and unicellular fungi have clonal rather than sexual population structures, which has major consequences for medical research and practice. Plasmodium falciparum, the agent of malaria, is a special case: the scarce evidence available is contradictory, some suggesting that uniparental lineages may exist in nature. This is puzzling (because P. falciparum is known to have a sexual stage) and poses a challenge that can be readily settled by ascertaining the frequency distribution of genotypes in natural populations.

Animals↗
PubMed1991

A family of repeated DNA sequences in Toxoplasma gondii: cloning, sequence analysis, and use in strain characterization.

A Toxoplasma gondii genomic library was constructed in lambda EMBL3. Repeated fragments were detected by hybridization with radiolabeled total DNA from the parasite and one recombinant was chosen due to its strong hybridization signal. By using electrophoretic and hybridization analysis, four cross-hybridizating restriction fragments were selected and sequenced. The determined nucleotide sequence of these fragments (TGR1A, TGR1E, TGR2, and TGR4) has shown a complex system of conserved and degenerated repeats in which TGR1E corresponds to the most conserved element. This last sequence was used to investigate restriction fragment length polymorphisms among several T. gondii strains by Southern blotting.

Animals↗
PubMed1991

[Detection of homologous oncogene sequences in the genome of Plasmodium falciparum].

Homologous sequences of the acute RNA tumor virus oncogenes have been found to be highly conserved within vertebrates, insects and yeasts. In the present work, seven different oncogene DNA sequences have been used as probes to search for homologous sequences in the DNA of the protozoan Plasmodium falciparum. Both the v-fms v-Ha ras probes hybridized P. falciparum DNA. The oncogene study will allow an understanding of the biology of the parasite and particularly the host-parasite relationships which allow P. falciparum to develop, keeping the established harmony between the parasite and his host.

Animals↗
PubMedDate not supplied

[Immunization against human malaria: present knowledge].

The authors review different aspects of immunization against malaria according to the different stages of the parasitic cycle of Plasmodium falciparum: sporozoite vaccine preventing organism infestation, merozoïte vaccine and gametocyte vaccines preventing the accomplishment of the sexual cycle. Progress of molecular biology and better knowledge of cellular immunity provide some prospects regarding parasitic vaccinology, thanks to genetic engineering. Recombinant vaccines in vitro, in vivo and synthetized are under study and provide the best prospects regarding immunization against human malaria.

Animals↗