Beaucoup de parasites à cycle complexe ont développé la capacité d’altérer le phénotype de leurs hôtes. Il est reconnu que ces modifications d’apparence ou de comportement sont responsables d’une augmentation de la probabilité de prédation de l’hôte intermédiaire par l’hôte définitif. Ce phénomène de manipulation parasitaire peut avoir de nombreuses conséquences à l’échelle de l’écosystème, modifiant les interactions entre les populations d’hôtes et bouleversant leur rôle écologique. Cependant, les parasites manipulateurs sont peu étudiés sur le plan écologique, et l’effet de l’environnement sur l’interaction entre ces parasites et leurs hôtes, notamment en termes de manipulation, est encore largement inconnu. Au cours de cette thèse, j’ai étudié l’effet de l’environnement sur l’interaction entre les gammares, des crustacés amphipodes de grande importance écologique dans les rivières, et leurs parasites acanthocéphales. Mes travaux ont montré que les conditions de ressources alimentaires et de température subies par les hôtes durant le développement des parasites influençaient plusieurs paramètres de l’infection mais n’affectaient pas la manipulation en termes d’utilisation de refuges. Toutefois, tandis que la géotaxie ne dépendait pas non plus de la température, l’impact des parasites sur la phototaxie des gammares était plus fort à haute température. De plus, mes travaux ont montré que l’impact conjoint de la température et des parasites pouvait modifier le rôle détritivore des gammares. Dans un contexte de changements globaux, ces travaux permettent de mieux comprendre l’importance de l’impact des parasites sur leurs hôtes et en prévoir les conséquences écologiques. / Many parasites with complex life cycle have developed the ability to alter the phenotype of their hosts. It is recognized that such changes in appearance and behavior are responsible for an increase in the probability of predation of their intermediate hosts by their definitive hosts. This phenomenon of parasite manipulation can have numerous consequences at the scale of the ecosystem, modifying the interactions between host populations and altering their ecological role. However, manipulative parasites received little attention from an ecological point of view. Thus, the effect of the environment on the interaction between these parasites and their hosts, in particular in terms of manipulation, is largely unknown. In this thesis, I studied the effect of the environment on the interaction between gammarids – ecologically important crustacean amphipods in rivers – and their acanthocephalan parasites. My experiments showed that the conditions of food resources and temperature experienced by gammarids during the development of their parasites influenced several infection parameters, but did not affect behavioral manipulation in terms of use of refuges. Nevertheless, while the geotaxis was not either effected by temperature, the impact of parasites on gammarids phototaxis was stronger at high temperature. Moreover, my studies showed that the cumulative effect of temperature and parasitism could alter the shredder role of gammarids. In a context of global changes, this work provides a better understanding of the importance of the impact of parasites on their hosts, allowing to make previsions on their subsequent ecological consequences.

Les interactions hôte – parasites sont des systèmes qui affectent probablement la totalité des êtres vivants et constituent un facteur clé dans la compréhension de la dynamique des maladies infectieuses. On a abordé cette problématique en utilisant le système Fasciola hepatica/Lymnaeidae dans sur l'île de Cuba. Cette thèse utilise une approche basée sur différentes disciplines de la biologie comme l’écologie des populations (distribution et abondances de mollusques hôtes intermédiaires), l'écologie parasitaire (données de prévalences naturelles de parasites chez les hôtes), la génétique des populations en utilisant des marqueurs microsatellites (tant pour le parasite que pour les mollusques hôtes), et des études de susceptibilité et compatibilité douve/limnée.En ce qui concerne la diversité génétique du parasite, une très haute diversité et une forte probabilité d’allofécondation ont été observées. En revanche, on n’a pas trouvé de différentiation significatives entre souches. Les taux d’infection chez le bétail sont très élevés.Pour ce qui est de la biologie des populations des limnées hôtes, on a cartographié la distribution des deux espèces présentes à Cuba : Galba cubensis qui est très répandue et Pseudosuccinea columella qui n'est présente que dans la partie centre-occidentale. Nous avons mis en évidence des différences concernant les types d’habitats préférés pour chaque espèce : G. cubensis est plus plastique écologiquement et se retrouve beaucoup plus dans les sites anthropisés.L'étude des compatibilités douve/mollusque a révélé l’existence de populations avec une résistance naturelle à l’infection par F. hepatica chez la limnée P. columella. Ces populations sont génétiquement différenciées des populations sensibles. La plupart des populations sensibles sont monomorphes avec le même haplotype très répandu. Par contre, on a observé une diversité génétique plus importante chez G. cubensis qui suggère un temps évolutif plus ancien à Cuba. L’échantillonnage fait dans une aire de où la fasciolose sévit fortement chez le bétail a révélé un très faible taux d’infection naturel chez les limnées, mais avec de fortes variations d'intensités. Différentes combinaisons douve/limnée sympatriques et allopatriques testées expérimentalement ont montré une compatibilité supérieure de G. cubensis qui suggère une meilleure adaptation aux souches de F. hepatica cubaines.Les résultats obtenus montrent que la compréhension de la dynamique des maladies infectieuses ainsi que leur contrôle doivent s’appuyer sur des connaissances très solides de la biologie, écologie, génétique et évolution des systèmes hôtes – parasites. / Host – parasite interactions are biological systems that probably affect every living being. It also constitute a key factor in the understanding of infectious diseases. This subject has been studied using the Fasciola hepatica/Lymnaeidae system in the insular environment of Cuba. This thesis makes a biological multidisciplinary approach through population ecology (distribution and abundance of intermediary hosts snails), infection rates estimations of parasites in their hosts, population genetics using microsatellites markers (for both parasite and snails hosts), and studies of susceptibility and compatibility fluke/snail.The genetic diversity of the parasite is characterized by high values of diversity as well as probability of cross fertilization. However, we failed to detect significant differences between the strains but a highly infection rate is shared in cattle.Regarding the lymnaeid snails, the distribution of the two occurring species is mapped showing that Galba cubensis is widely distributed while Pseudosuccinea columella only exists in central-western Cuba. Both snail species differ in preferred habitat types and G. cubensis displays a higher ecological plasticity commonly observed in heavily human-transformed sites.Differences in host-parasite compatibilities have been revealed. It has been noted the existence of some populations of P. columella with a natural resistance to F. hepatica infection which display a marked differentiation of their population genetic structure compared to susceptible populations. Most susceptible populations are monomorphic with a very common haplotype in Cuba. Conversely, we observed a higher diversity in G. cubensis indicating a larger evolutionary time in Cuba. The sampling conducted in a fasciolosis endemic area revealed very low prevalences in the snail populations. However, strong variation in parasite mean intensity within individuals supports the high infection rates observed in cattle. Different sympatric and allopatric fluke/snail combinations were experimentally tested in which G. cubensis proved to be more compatible and suggest a better adaptation to the circulating F. hepatica in Cuba.Our results show that the understanding of infectious diseases’ dynamics and their effective control must strictly rely in a full knowledge of the biology, ecology, genetics and evolution of host – parasite systems.

Depuis 2006, une recrudescence de cas de protostrongylose, parasitose liée à la présence de nématodes au niveau pulmonaire, apparaît dans le Sud-est de la France au sein de la population de lièvres européens (Lepus europaeus). Le cycle de développement de ces parasites nécessite le passage obligatoire par un hôte intermédiaire connu pour être un mollusque gastéropode terrestre. Notre programme a pour objectif l'étude épidémiologique de la maladie et notamment l'identification des acteurs du cycle parasitaire.Basée sur une analyse morphologique et moléculaire, nous identifions : Protostrongylus pulmonalis (Frölich, 1802) fréquemment inventorié en Europe et P. oryctolagi Babos, 1955, décrit à une seule occasion en Hongrie en 1955, comme les agents responsables de la protostrongylose en France. Cette étude a permis de déposer de nouvelles séquences d'ADN de référence, utiles pour l'identification ultérieure de nos espèces parasites, en particulier les stades larvaires et sur lesquelles nous nous sommes basées pour la reconnaissance des hôtes intermédiaires intervenant dans le cycle naturel. Sur 3622 mollusques analysés, nous avons mis en évidence des larves de stade 3 (P. pulmonalis et P. oryctolagi) à partir de 18 individus, appartenant à la famille des Hygromiidae et dont l'identification spécifique repose sur différents marqueurs moléculaires (de loin préférables aux critères morphologiques). Au sein des populations de lièvres, nous identifions l'âge et l'environnement, en lien avec la répartition des hôtes intermédiaires comme les facteurs de risque de la maladie. Le parasitisme, concernant près de 55% des animaux, n'a pas eu d'effet mesurable sur l'état général de l'hôte, mais pourrait être impliquée dans une diminution de la fécondité des hases, suggérant un impact potentiel sur les dynamiques de populations de lièvres. / Since 2006, in the South-East of France, we observe an increase in the number of hares (Lepus europaeus) suffering from pulmonary protostrongyliasis, which is a parasitic disease caused by nematodes in the lungs. The development cycle of these parasites requires the obligatory pathway through an intermediate host, terrestrial gastropod mollusk. Our goal was the epidemiological study of the disease, particularly the identification of the parasite cycle.Based on morphological and molecular analysis, we identified two causative agents of pulmonary protostrongyliasis in France: Protostrongylus pulmonalis (Frölich, 1802) frequently inventoried in Europe and P. oryctolagi Babos, 1955 described only once in Hungary in 1955. Thus new reference sequences of DNA are available, which is useful for the subsequent identification of our parasite species and particularly for larvae-stage, allowing the recognition of intermediate hosts involved in their natural cycle. In total 3622 terrestrial mollusks were analyzed. We identified three-stage larvae of P. pulmonalis and P. oryctolagi from 18 individuals belonging to the family of Hygromiidae and belonging to several species identified with different molecular markers. In the hare populations, we identify the age and environment (in association with the distribution of intermediate hosts) as risk factors for the disease. The parasite, with approximately 55% of infected animals, had no measurable effect on the health status of the host, but could be involved in a decrease in the fecundity, suggesting a potential impact on population dynamics of hares.

This work allowed the first characterization of the three members of the chloride channel CLC family in T.brucei. The TbCLCs are expressed in the two proliferative stages of the parasite and two of their members appear non-essential. The three TbCLCs act as chloride transporters in X.laevis oocytes and some of their biophysical properties were determined. Furthermore, TbCLC-b appeared to be involved in lysis by the human innate immunity protein apoL-1<p>A novel function of T.brucei adenylate cyclases was discovered in their ability to suppress expression of the innate immunity protein TNF-α. The suppression of the innate response occurs before the first peak of parasitemia and reduces the host ability to control the parasite.<p> / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Call number: LD2668 .T4 1979 S73 / Master of Science

Call number: LD2668 .T4 1986 C374 / Master of Science / Plant Pathology

The work presented in this thesis is focused upon the community of endemic pathogens of African cattle in Sub-Saharan Africa, which has long constrained livestock production in these areas. The first aim of this work is to investigate whether the pathogen community as a whole shapes the ensuant epidemiology and morbidity which are currently attributed to any of its individual pathogens. The second aim is to determine if a greater understanding of the interactions present amongst genetically distinct parasites of the same species can be used to better explain epidemiological features that are at present poorly understood. Emphasis is placed on examining spatial variation in the epidemiology of Theileria parva, a tick-transmitted protozoan that causes East Coast Fever. To achieve these aims, this work examines field data collected from a large and comprehensive study conducted in south east Uganda. Through application of apposite statistical techniques and mathematical modelling, aspects of the complex relations amongst the pathogen community and their environment are explored. Evidence is presented that demonstrates the paramount role of the pathogen community as a whole in shaping the infection dynamics and pathogenicity of any of its individual components. By focusing on a single member of this pathogen community (Theileria parva), some of the influences of host, vector, geographical location, temporal dynamics and intra-species pathogen interactions are elucidated. Application of a polymorphic molecular marker to Theileria parva infected blood samples and the use of Cox proportional hazard analysis, show variability in the survival of infections in cattle in high and low tick challenge areas. Moreover infection survival, which plays a pivotal role in parasite transmission, is shown to be a function of the interactions established amongst genetically distinct co-infective parasites. In consequence, vector intensity alone is insufficient to develop reliable transmission models which can accurately predict the epidemiology of the parasite inside and outside enzootic belts. Finally, a theoretical model is developed which, based upon the field evidence obtained throughout this work, provides a possible explanation for the mechanics of T. parva survival in cattle. In summary, this thesis makes a case that consideration of both inter- and intra-species pathogen interactions, can greatly augment understanding of the epidemiology of these pathogen communities. An integrated approach to pathogen dynamics can better equip an integrated approach to control of important diseases of African cattle.

This thesis examines the parasite dynamics and the mechanisms affecting parasite load and transmission focalising on the role played by host and habitat heterogeneities. This study is based on the gastrointestinal nematode Heligmosomoides polygyrus and the small mammal yellow necked mouse and uses data gathered from experimental field manipulations of parasites intensities and data gathered from trapping monitoring. Initially the parasite community of yellow-necked mouse (Apodemus flavicollis) was explored in North-Eastern Italian Alps with the aim to describe the major patterns and identify the factors affecting parasite community structure. Despite the observed spatial variability it has been found that differences within the host population such age and secondly sex and breeding conditions, were the major factors acting on parasite occurrence and intensity. Habitat differences had a less apparent effect on parasite community structure. The consequences of H. polygyrus infection on other parasite species infections have been analysed, in specific the infestation of the tick Ixodes ricinus in populations of A. flavicollis. H. polygyrus load and tick infestation were monitored as well as were carried out field manipulations of H. polygyrus intensity and were monitored changes in tick infestation. It has been found that H. polygyrus load was negatively related to I. ricinus infestations. Host factors mediated the H. polygyrus-I. ricinus interaction such that young and non-breeding mice exhibited higher I. ricinus to H. polygyrus intensity respect breeding adults. The role of host sex on parasite abundance was then investigated carrying out a field experiment where the H. polygyrus intensity were manipulated in relation to mice gender. In specific, H. polygyrus was removed alternately from either sexes and the parasite load was analysed in the untreated sex. It was found that males mice were responsible to drive parasite transmission in the host population and this was observed in absence of sex-bias in parasite infection, suggesting that this pattern was not a mere consequence of quantitative differences in parasite loads between sexes. To disentangle the possible mechanism causing this sex bias in parasite transmission mathematical simulations based on parameters obtained for the field experiment were used. Two non mutually exclusive hypotheses causing sex bias in parasite transmission were tested: a- males immune response is less efficient and this causes the development of more successful parasite infective stages or b-males behaviours allow them to be more efficient is spreading in more exposed areas parasite infective stages. Multi-host models were developed and simulations were compared with field results. While it was not disentangled the most dominant mechanism causing sex bias in parasite transmission this study underlined the importance of host sexes in affecting parasite dynamics and host-parasite interaction. In conclusion this thesis highlighted the importance of considering host and environmental differences when investigating host parasite interactions. This finding could be extremely important when planning measured of disease control or to avoid disease outbreak. Controlling target group of individuals host could avoid economical losses and a more effective measure of intervention.

Schizophrenia is a devastating mental disorder that affects around 1% of the world’s population, characterized by the presence of positive symptoms including hallucinations and delusions, negative symptoms including depression and anxiety, and cognitive impairment including deficits in speech and memory. The complete etiology of schizophrenia is not yet understood, though it is known that both genetics and environmental factors play a role. One environmental factor, a chronic cerebral infection by the parasite Toxoplasma gondii, has one of the highest correlations with schizophrenia of any environmental factor, and may play a role in the pathology of the disease. This is especially true in the case of Type I toxoplasma, which is the most virulent of the three common strains of the parasite. Toxoplasmosis causes an increase in dopamine levels in the striatum and substantia nigra through the production of two enzymes that mimic the rate limiting enzyme in dopamine synthesis, tyrosine hydroxylase. Increased dopamine concentrations in these areas are experimentally correlated with positive schizophrenia symptoms. In addition, toxoplasmosis causes chronic upregulation of the kynurenine pathway via INF- release, leading to chronically elevated kynurenic acid levels. This leads to dysfunction of the glutamatergic system via (1) the binding and inhibition ofα7- nicotinic receptors, leading to decreased GABAergic inhibitory activity in the hippocampus and decreased glutamate release in the prefrontal cortex, and (2) NMDA and AMPA receptor hypofunction, causing decreased inhibitory signaling by GABAergic neurons leaving glutamatergic neurons in a hyper-excitable state. These mechanisms, compounded by commonly identified mutations in the genes of schizophrenic individuals affecting the dopaminergic system, the kynurenine pathway,α7-nicotinic receptors, and the glutamatergic system, create a viable theory as to how the interplay between genetics and toxoplasmosis could cause schizophrenia.

No description available.