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M Tibayrenc

Publications and source records attributed to M Tibayrenc.

At least 19 recordsLinked to original sources
PubMed1992

Characterization of Chilean, Bolivian, and Argentinian Trypanosoma cruzi populations by restriction endonuclease and isoenzyme analysis.

Ninety-one Chilean, 15 Bolivian, and 9 Argentinian Trypanosoma cruzi stocks, isolated from various hosts and vectors, were characterized by schizodeme analysis with EcoRI and MspI endonucleases. The three major similar pattern groups that emerged from this sample correlated with results of isoenzyme analysis. This result confirms previous work and supports the hypothesis of the clonal structure of natural populations of T. cruzi, fully defined at the level of isoenzyme analysis, quantitative kinetoplast DNA restriction fragment length polymorphism, and kinetoplast DNA hybridization analysis. In Chile, sylvatic and domestic cycles of T. cruzi transmission appear to be mainly independent: genetically different families of natural clones are specific to these cycles. Nevertheless, the possibility of overlap remains unclear. Results described here indicate that natural clones inhabiting Chilean regions appear genetically related to the natural clones identified in neighboring countries. In Chile the more frequently sampled parasite types are natural clone 39 and a genetically closely related clone NP13. In this work an evaluation of T. cruzi natural clone mixtures in T. cruzi stocks from Chile was performed for the first time by schizodeme analysis before and after serial transfer in mouse maintenance. The results indicate that six of nine stocks are composed of two or more natural clones. This observation raises the relevant question of whether specific T. cruzi natural clones generate different clinical features of Chagas' disease.

Animals↗
PubMed1992

Direct identification of Trypanosoma cruzi natural clones in vectors and mammalian hosts by polymerase chain reaction amplification.

The polymerase chain reaction was used to amplify the highly variable region of the kinetoplast minicircle of Trypanosoma cruzi directly in biological samples (feces of infected Triatomine bugs, blood samples of experimentally infected mice, and artificially infected human blood samples). Hybridization of the amplified DNAs with reference stocks representing different genotypes (natural clones) enabled us to characterize the stocks infecting the biological samples under study. The main interest of this new approach is the diagnosis of T. cruzi infection and simultaneous direct identification of the different natural clones circulating in vectors and mammalian blood without isolation of the stocks. The suitability of this technique for epidemiologic studies is also discussed.

Animals↗
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

Clonal defence.

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Animals↗
PubMed1991

Multilocus isozyme identification of Trypanosoma brucei stocks isolated in central Africa: evidence for an animal reservoir of sleeping sickness in Congo.

Six Congolese and 3 Zairian Trypanosoma brucei stocks were studied by isozyme cellulose acetate electrophoresis. Twenty isozyme systems were used, of which only 5 showed variability. These 5 polymorphic systems made it possible to identify 5 different zymodemes. Zymodemes isolated from man were recorded both from pig and sheep too, which confirms the results of previous authors. This favors the existence of an animal reservoir of human African trypanosomiasis in the Congo, which could play a role in the transmission of the disease, at least by the maintenance of residual foci.

Animals↗
PubMed1991

[SDS-PAGE analysis of surface proteins and antigens evidences high heterogenity in natural clones of Trypanosoma cruzi, correlated with isoenzyme variability].

Surface protein and surface antigen patterns of 19 Trypanosoma cruzi laboratory clones, representing 17 different isozymic profiles (zymodemes), were compared by SDS-PAGE analysis. Surface protein patterns were found to be complex and heterogeneous. According to the number of common bands, we calculated similarity coefficients of surface protein patterns on the one hand, and of surface antigen patterns on the other hand, for 33 stock pairwise comparisons. In both cases, these coefficients were statistically correlated to the isozyme index of genetic identity. Such a correlation between independent genetic markers favours the clonal structure of T. cruzi natural populations previously evidenced. Moreover, we did not observe any notable differences in the surface antigen pattern among 4 T. cruzi cloned stocks precipitated by homologous as well as heterologous hyperimmune sera. The immunological significance of the molecular weight variability in surface antigen patterns among different zymodemes is discussed.

Animals↗
PubMed1991

General procedure to construct highly specific kDNA probes for clones of Trypanosoma cruzi for sensitive detection by polymerase chain reaction.

Our strategy of probes designing for major clones of Trypanosoma cruzi was performed taking into account the: (i) clear identification of the major clones under multilocus study; (ii) hypothesis of a parallel evolution between the extranuclear and nuclear markers; (iii) structure of kDNA which allowed to amplify high variable regions of the minicircle (HVRm) by PCR. The large production of HVRm was very useful to test their ability to be used as probes for detection of DNA from a diversified genetic panel of T. cruzi. Our success in designing such probes has important implications on: the enhancement of 2 evolutive hypothesis about the clonal structure of T. cruzi and the parallel evolution of their extranuclear and nuclear genetics markers; direct diagnosis in patients and vectors. Studies on bio-clinical significance of major clones are discussed. This procedure could be used as a general strategy to generate DNA probes for Kinetoplastida.

Animals↗
PubMed1990

A clonal theory of parasitic protozoa: the population structures of Entamoeba, Giardia, Leishmania, Naegleria, Plasmodium, Trichomonas, and Trypanosoma and their medical and taxonomical consequences.

We propose a general theory of clonal reproduction for parasitic protozoa, which has important medical and biological consequences. Many parasitic protozoa have been assumed to reproduce sexually, because of diploidy and occasional sexuality in the laboratory. However, a population genetic analysis of extensive data on biochemical polymorphisms indicates that the two fundamental consequences of sexual reproduction (i.e., segregation and recombination) are apparently rare or absent in natural populations of the parasitic protozoa. Moreover, the clones recorded appear to be stable over large geographical areas and long periods of time. A clonal population structure demands that the medical attributes of clones be separately characterized; ubiquitous clones call for priority characterization. Uniparental reproduction renders unsatisfactory Linnean taxonomy; this needs to be supplemented by the "natural clone" as an additional taxonomic unit, which is best defined by means of genetic markers.

Animals↗
PubMed1989

Chagas' disease in Bolivia: clinical and epidemiological features and zymodeme variability of Trypanosoma cruzi strains isolated from patients.

We performed serological and pathological studies on 495 patients with Chagas' disease from different areas of Bolivia. Eighty-nine Trypanosoma cruzi strains, isolated by xenodiagnosis, were characterized by 12 isoenzyme loci and were related to the presence of cardiac changes and enteric disease with megacolon. There was a high heterogeneity of human zymodemes, presenting evidence of 2 predominant zymodemes genetically dissimilar from each other and ubiquitous in Bolivia. The frequencies of these predominant zymodemes among strains from patients were compared to strains from triatomine bugs previously studied. We observed mixtures of different zymodemes within the same patient, a phenomenon seen previously in Bolivian patients. There was no apparent difference of pathogenicity between the 2 more frequent zymodemes isolated from humans.

Animals↗
PubMed1988

Linkage disequilibrium in natural populations of Trypanosoma cruzi (flagellate), the agent of Chagas' disease.

We have studied linkage disequilibrium in natural populations of Trypanosoma cruzi, the agent of Chagas' disease, by analyzing (i) a set of 524 stocks from the whole geographical range of the parasite, characterized at four gene loci coding for enzymes; (ii) a subsample of 121 stocks characterized at 12 enzyme loci; and (iii) a subset of 386 stocks from six locations in Bolivia, characterized by four enzyme loci. Our results show that the linkage disequilibrium reaches the maximum possible value, given the observed allelic frequencies, for almost all the locus pairs. This result is most consistent with the hypothesis that genetic recombination is absent or very rare in T. cruzi natural populations. Partition of the linkage disequilibrium variance for the six Bolivian populations shows that both inter- and intrapopulation components are substantial and that the relationships among the components are D2IS less than D2ST, and D'2IS less than D'2ST. These inequalities are interpreted as the result of an interplay between genetic drift, rare or absent mating, and clonal selection in generating linkage disequilibrium in T. cruzi populations.

Alleles↗
PubMed1987

Exotic stock of Trypanosoma cruzi (Schizotrypanum) capable of development in and transmission by Triatoma protracta protracta from California: public health implications.

A stock of Trypanosoma cruzi was recovered from a Triatoma dimidiata from Tegucigalpa, Honduras. This stock was shown to be capable of development and transmission by native California Triatoma protracta protracta. Isozyme analysis indicated that this T. cruzi is closely related to the Tehuantepec strain and to a lesser extent the Miles' zymodeme 1 strain. The potential public health significance of development and transmission of exotic stocks of T. cruzi by native reduviids is discussed.

Animals↗
PubMed1987

[High correlation between isoenzyme classification and kinetoplast DNA variability in Trypanosoma cruzi].

By means of 14 restriction enzymes, we have studied the kinetoplast DNA polymorphism in 21 Trypanosoma cruzi isolates previously classified into 19 different genotypes based on the analysis of 15 isozyme loci. We have found a high correlation (p less than 0.001) between the proportion of restriction bands (fragments) common to any two given isolates and the corresponding genetic identities calculated from the isozyme data. This shows that the two classifications (kDNA and isozymes) corrobate one another and strongly suggests that the two types of variability are correlated with time (molecular clocks). The phylogenic classifications so obtained can be used as rational bases for medical and epidemiological studies. Although they are correlated, the two types of analysis are complementary as they do not yield identical results. Like the isozyme genetic distances and genetic identities, the values obtained for the proportion of common restriction bands (fragments) exhibit a continuum. This seems to confirm that natural T. cruzi populations exhibit a wide range of genotypes rather than a few well-differentiated clusters of strains.

Animals↗
PubMed1986

Additional data on Trypanosoma cruzi isozymic strains encountered in Bolivian domestic transmission cycles.

We have collected in Bolivia 212 stocks of Trypanosoma cruzi from domestic transmission cycles and have assayed for nine enzyme systems (11 gene loci). Only a few different isozyme profiles exist, without recombination between them, a situation also encountered in previous Bolivian samples. The 212 stocks, combined with 207 stocks previously studied, have been analysed to uncover any spatial patterns. The frequency of heterozygous strains (2 and 2a) decreases westwards and with increasing altitude. Given that longitude and altitude are correlated with each other, it is not possible to decide which of these two geographic variables is the relevant one, or if both are. These associations might be due to climatic factors. Studies by other authors have shown, however, that heterozygous strains are rare or absent in the Amazon Basin, which is at low altitude.

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