Biomedical subjects
C Combes
Publications and source records attributed to C Combes.
Fitness of parasites: pathology and selection.
Parasites improve their fitness as a result of the selection of traits which determine their relationships with their hosts. Some of these relationships are examined briefly. There is a cost of virulence for parasites, paralleling the cost of resistance for hosts, which implies that the good health of the host can be a component of parasite fitness; conversely, some transmission modes imply that the host be markedly weakened by the parasite. Pathogenicity can be influenced by characters such as a transmission of the parasite from parents to offspring, or the demographic characteristics of the host populations. Important components of parasite fitness are: the complexity of the life-cycle; the degree of specialization for a more or less open host range; the conspicuousness or discretion of the infective and parasitic stages. However, the best possible adaptation to a particular host is not always selected: when a parasite exploits several host species, the gene flows between parasites which have developed in different hosts may be responsible for "maladaptation". This may be important for an understanding of the pathogenicity of certain human parasitic diseases.
[Host spectrum and virulence].
In an anthropozoonoses distribution of an infectious agent population into several host species at each generation can be considered to result in a fragmented anthropozoonoses environment. Insofar as reproductive success may vary between host species, gene flow becomes asymmetric and a source-sink anthropozoonoses system may be created. Under these conditions optimal virulence may be occur in any host species so that the source host species exerts the strongest selective pressure on the infectious agent. In the sink host species the virulence of the parasite may be sub- or super-optimal (stable misadaptation). This explains the gravity of parasitic infections that man shares with animals and the fact that virulence does not diminish with time.
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.
[Imagery of human immunodeficiency virus (HIV) encephalitis].
The authors present the different aspects of HIV encephalitis in CT and MR in a series of 15 patients with anatomopathological proof. Atrophy was the most commonly found lesion (12 patients) and could rapidly be evolutive. White matter lesions (9 patients) were more of ten nodular than diffuse. They were better demonstrated by MRI and did not enhance after intra-venous injection of DOTA-gadolinium. A frequent association with opportunistic infections (toxoplasmosis: 10 patients, CMV:2 patients), lymphoma (4 patients), or PML (3 patients) was observed which emphasized the low specificity of brain imaging in patients with HIV encephalitis.
Behaviours in trematode cercariae that enhance parasite transmission: patterns and processes.
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[Schistosoma, water and man].
The biology of schistosomes is increasingly better known due to the research works conducted since the early 1980s. Numerous data have been collected on: the structure of the genome; the genetic variability of natural populations; the causes of geographical distribution of Schistosoma species; the acquisition, probably recent, of the parasite as by modern man's ancestors; and even some aspects of development, such as the behaviour of larvae and the migrations in the circulatory system. Substantial advances have also been made in the maintenance of laboratory strains. Yet, multiple and fascinating problems are still raised by schistosomes. In the present state of our knowledge the origin and relationship of human parasitizing species are still hypothetical. Several features of reproduction, such as the existence of separate sexes and permanent couples cannot be explained. Quantitative data concerning the dynamics of transmission are much too vague to establish satisfactory mathematical models and to contribute usefully to strategies of control. Finally, the fact that schistosomes can develop either in man alone or in numerous mammals remain a mystery for immunologists and specialists of evolution.
Genetic variability and evolution of the Schistosoma genome analysed by using random amplified polymorphic DNA markers.
The usefulness of random amplified polymorphic DNA markers (RAPD) was assayed in an attempt to discriminate among species, strains and individuals within the genus Schistosoma. Depending on the species, 40-50 arbitrary decamer oligonucleotides were used as primers to amplify total DNA by the polymerase chain reaction (PCR). An important polymorphism was observed among 5 species, allowing a phylogenetic tree to be outlined. These differences can be used for rapid and accurate identification. A limited but easily detectable polymorphism was revealed among 3 strains of a single species (Schistosoma mansoni). Minor differences were observed among individuals of a single strain. A RAPD marker allows sexual discrimination between individuals from the terminal spined-egg species group. Although a limited number of strains have been examined, the results already indicate clearly that RAPD markers constitute a powerful tool for the analysis of genetic variability. This new tool will considerably extend the information available from morphology, isozyme and limited restriction fragment length polymorphism data and opens the way to genetic analysis of these species.
Experimental host-induced selection in Schistosoma mansoni strains from Guadeloupe and comparison with natural observations.
Allelic frequency variation at the malate dehydrogenase (E.C.1.1.1.37) polymorphic locus (Mdh-1) was analysed during several successive generations in four strains of Schistosoma mansoni from Guadeloupe, maintained experimentally on mice. A rapid evolution of the frequency of the Mdh-1a allele is interpreted as being the result of an interaction between experimental drift and selection induced by the murine laboratory host. These experimental results are compared to the genetic structures observed among the corresponding natural populations of S. mansoni in Guadeloupe (West Indies). They strengthen the hypothesis of a natural host-induced selection by the murine host (Rattus rattus), which, in Guadeloupe, plays the role of host reservoir for this human schistosome.
[Arguments for the modification of the genome (introgression) of the human parasite Schistosoma haematobium by genes from S. bovis, in Niger].
Characterization of schistosome populations from human in eastern Niger, through intra-uterine egg morphology of female parasites and phenotopic analyses of worms observed for acid phosphatase using electrophoretic separation, renders results that suggest an intogression of S. haematobium from man by genes of S. bovis, a parasite of domestic livestock. The origin of this introgression, that could implicate S. curassoni as well, another livestock parasite that hybridize with S. bovis, is discussed.
Functional exploration of brain vessels by MRI. Usefulness of presaturation techniques.
The authors report an original method to explore vascular structures. This method combines the presaturation technique with gradient-echo vascular imaging, and it makes it possible to obtain qualitative data complementing those obtained by digital subtraction angiography in cerebral vascular pathology.
Contribution of computerized tomography to the diagnosis of acute cerebral ischaemia.
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Atypical MR presentation of Wilson disease: a possible consequence of paramagnetic effect of copper?
A 53-year-old patient with Wilsons's disease and without autonomic dysfunction presented on T2-weighted MR study an atypical decreased signal intensity of the putamina and the caudate nuclei. Possible explanations of such a signal abnormalities are discussed.
Molecular evidence linking hominid evolution to recent radiation of schistosomes (Platyhelminthes: Trematoda).
Molecular phylogenies for seven species of schistosomes, including four species infecting man, were constructed from PCR-amplified sequences of two ribosomal genes: one nuclear (internal transcribed spacer 2 in the ribosomal multigenic family) and one mitochondrial (16S rDNA). The two phylogenies obtained are congruent, and the data suggest that the mitochondrial sequence evolves about three times faster than the nuclear sequence. We propose a calibration of the phylogenetic tree of schistosomes that dates "human capture" of these parasites from other animal hosts (rodents and ruminants) in Africa to 1-10 million years ago, when the first hominids invaded savanna areas, which are the favorable environment for parasite transmission.
Abundance/host size relationship in a fish trematode community.
The abundance of six species of trematodes: Aphanurus stossichi, Bacciger israelensis, Diphterostomum israelense, Plagioporus idoneus, Leprocreadium album and L. pegorchis, parasitic in the digestive tract of marine teleostei (Sparidae) collected near Jounieh (east Mediterranean), was analysed as a function of the host-size. In two parasite/host systems, infections were observed from the lowest size classes of the sample, with a clear tendency to an increase of abundance in older fish. In four others, parasites appear only above a rather high threshold class, young individuals never being infected. In the last three parasite/host systems, host invasion may occur early or late, but infection decreases above a well defined size class, old fishes rarely or never being infected. A given trematode species, when parasitizing several host species, shows similar abundance/host size relationships, e.g., P. idoneus in Diplodus vulgaris and Oblada melanura. When more than one species of trematode infects a single host species, curves can be markedly distinct; for instance, L. pegorchis was collected from Pagellus erythrinus below 15 cm. whereas D. israelense parasitized the same fish approximately above the same size. There is no evidence that such a replacement of one trematode by another in the course of host growth is a result of inter-specific competition.
Relocation of Schistosoma mansoni in the lungs and resistance to reinfection in Rattus rattus.
The localization of adult Schistosoma mansoni originating from Guadeloupe (West Indies) was analysed in the natural host Rattus rattus in experimental and natural infections. A transfer of schistosomes from the porto-mesenteric system to the lungs occurs between the 4th and the 20th weeks post-infection, with a peak between 4 and 8 weeks; it should be noted that the worms start laying eggs at 4 weeks post-infection. In both experimentally and naturally infected R. rattus the relocation of schistosomes in the lungs is correlated with the total worm burden. Between 6 and 12 weeks post-infection some adult worms and numerous eggs are trapped in the liver. A high mortality in the worm population coincides with the migration of the parasites from the porto-mesenteric veins to the lungs. In re-infected R. rattus a relationship appears between the presence of schistosomes in the lungs and resistance to reinfection. It is concluded that, as already postulated previously in mice, resistance to re-infection in the natural host R. rattus is at least partly correlated with the hepatic pathology caused by the schistosomes of the primary infection.
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.
[Uterine phlebography in pelvic venous stasis].
Pelvic veins opacification is very helpful in the diagnosis of vascular pelvic pain. First applied to intrauterine vascularisation and hypoplasia research, hysterophlebography allow the venous side of stasis to be obvious. 1) Normally, a fine intra-parietal network draining in intrauterine peripheric vein (arcuate network) is patterned by the contrast medium. For that 4 vessels roots are leaving: 2 lumbo-ovarian pedicles joining uterine venous side und tubal veins and extending over lumbo-ovarian pedicle; 2 uterine pedicles resulting from 2 uterine veins and receiving vesical veins located in the base of broad ligament. Contrast medium empties very quickly and almost the whole uterus emptying is lasting less than 10 seconds. 2) From a pathological point of view: a) in stasis, intrauterine veins pattern features are: intra-parenchymatous pictures of dilated venous network, local alterations pictures often secondary to thrombosis (9/10 on the left side) with intra-parenchymatous stasis and oblique anastomatic main vessels characterizing uterine veins thrombosis, more than 20 seconds emptying delay. Hysterographic and phlebographic times take advantage to be paired by visualizing mucous lesions (hypoplasia and polyp. endocervical and corporeal) in intra-parenchymatous stasis phenomena. b) Extrauterine stasis signs are characterized by preferentially right pedicles dilatation. Standing in upright position enhances stasis (proclive radiographies at 70 degrees). Dilatation is particularly located at the base of the broad ligament and gives to uterine veins with wide smeets a flexuous feature with wide contrasted clusters. Hence here emptying is slow and belayed.