No description available.

No description available.

No description available.

A study of myxozoan parasites has been investigated in hosts from freshwater environments in the UK. Over 17,000 oligochaetes, almost 5,000 juvenile cyprinids representing 7 species and over 60 invertebrate species have been examined for the presence of myxozoan parasites. In addition, studies on the lifecycle of Tetracapsuloides bryosalmonae (the causative agent of salmonid proliferative kidney disease, PKD) and of selected cyprinid myxozoans were conducted. A total of 21 actinospore types in seven collective groups were isolated and described from oligochaetes collected from seven different river systems in England and Wales. Twelve of the actinospores isolated appear to be new to science. Differences were noted in types of actinospores released at different sites and between seasons. Most actinospores were released from oligochaetes in spring and summer with prevalence of release ranging from 0.11% up to 5.83%. The most common actinospores were members of the collective group Echinactinomyxon with seven types identified, followed by the collective group Triactinomyxon, of which 6 types were identified. Five actinospores types were each encountered only once during the study. In juvenile cyprinid fish, 14 identifiable species of myxozoans in the genera Myxidium, Myxobolus and Sphaerospora plus three developmental stages were detected by histological examination. The most common myxozoans in cyprinids were Myxobolus pseudodispar and Myxobolus pfeifferi. Roach contained the most number of myxozoan species. Only seven myxozoan species were found in chub, but pathological responses and intensity of infections, particularly with M. pseudodispar, M. pfeifferi and Myxobolus buckei were greater when compared to other cyprinids examined. Juvenile cyprinids only appear to mount a pathological response to myxozoans once sporogony is initiated and some of those responses were considered severe enough to be detrimental to host survival. Mathematical models were produced using parasite data and incorporating a variety of data, including fish length, year class strength and environmental data to attempt to demonstrate a population level effect of disease. Many of the models developed clearly show that parasitism by Myxobolus spp. and Bucephalus polymorphus in juvenile fish is strongly correlated with population success in selected UK rivers. Laboratory experiments to transmit Myxobolus spp., Myxidium spp. and Sphaerospora spp. from selected cyprinid hosts to oligochaetes were unsuccessful. The most likely explanation is that the genetic strain of Tubifex tubifex used in the trials was not susceptible to infections by the myxospores selected. Specific DNA primers for Tetracapsuloides bryosalmonae were used on samples of over 60 invertebrate species collected from sites enzootic for PKD and on all 21 actinospore types isolated during the current study. All PCR reactions were negative for the presence of T. bryosalmonae DNA. Naive rainbow trout exposed to T. bryosalmonae spores from naturally infected bryozoans by bath challenge for 10 minutes developed PKD. Intraperitoneal injection of spores failed to induce the disease. The favoured route of entry by the parasite appears to be through mucous cells in the skin epithelium.

Toxoplasma gondii is an obligate intracellular protozoan parasite with a worldwide prevalence. Together with the causative agent of malaria (Plasmodium falciparum) and other medically important pathogenic parasites it belongs to the phylum of the Apicomplexa. Besides identifiable eukaryotic organelles, apicomplexan parasites differ from other eukaryotic cells by an extra set of specialised secretory organelles (micronemes, rhoptries and dense granules), that are sequentially secreted during invasion of the host cell. Upon host cell contact the apically located micronemes are the first organelles to be released and contain crucial virulence factors that are secreted. In order to systematically analyse vesicular traffic with a special focus on the secretory pathway of rhoptry and microneme proteins the ddFKBP system was used to perform a systematic analysis of Rab proteins in Toxoplasma gondii. Rab proteins are small GTP- binding proteins that are involved in targeting and fusion of vesicles from a donor to an acceptor membrane. Whereas higher eukaryotes like human cells encode more than 60 different Rab proteins apicomplexan parasites possess only a reduced core set of Rab proteins. Performing co-localisation studies with generated parasite lines expressing ddFKBPmyc-tagged versions of Rab1A, 1B, 2, 4, 5A, 5C, 7, 18 and Rab5B-ddFKBPHA revealed, that all these Rabs localise to the early secretory pathway (Rab1B, 2 and 18), the Golgi (Rab4), or the late secretory pathway (Rab5A, Rab5B, Rab5C and Rab7). No exact localisation could be defined for Rab1A. Rab5A and Rab5C, normally involved in endocytic uptake, were identified as important regulators of traffic to micronemes and rhoptries in Toxoplasma gondii, using an overexpression screen of Rabs and the analysis of trans-dominant mutants of promising candidates. Intriguingly, some microneme proteins could be found to traffic independently on functional Rab5A and Rab5C, indicating the existence of independent transport routes to micronemes, which again indicates that apicomplexans have remodelled Rab5-mediated vesicular traffic into a secretory system that is essential for host cell invasion. By using two-colour super-resolution stimulated emission depletion (STED) microscopy, distinct localisations of independent microneme proteins could be verified. This demonstrated that micronemal organelles are organised in distinct subsets or subcompartments. Given these results, it can be assumed that apicomplexan parasites modify classic regulators of the endocytic system to carry out essential parasite-specific roles in the biogenesis of their unique secretory organelles.

Bibliography: leaves 109-126. / xii, 126, [44] leaves, [34] leaves of plates : ill. (chiefly col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Crop Protection, 1997

Oomycetes (Stramenopiles, protists) are among the most severe plant pathogens, comprising species with a high economic and ecologic impact on forest ecosystems. Their diversity and community structures are well studied in terrestrial habitats, but tree canopies as huge and diverse habitats have been widely neglected. A recent study highlighted distinct oomycete communities in the canopy stratum compared to the ground region of three temperate deciduous trees (Quercus robur, Tilia cordata, Fraxinus excelsior). While the communities from the two strata were distinct when taking oomycete abundances into account, they were rather similar when only OTU presence/absence was considered. It remains, however, unknown if this homogeneity in the OTU presence also leads to a functional homogenisation among microhabitats within the two strata ground and canopy. In this study, we supplemented functional traits to oomycete communities in the tree microhabitats, which were determined over a time period of 2 years with a metabarcoding approach. Our results showed that even though most oomycetes occurred in all microhabitats, a strong discrepancy between the strata and correspondingly the distribution of oomycete lifestyles could be observed. This pattern was constant over several seasons. Obligate biotrophic species, exclusively feeding on living host tissue, dominated the canopy region, implying tree canopies to be a hitherto neglected reservoir for parasitic protists. OTUs assigned to the genus Hyaloperonospora—parasites highly specialised on hosts that were not sampled—could be determined in high abundances in the canopy and the surrounding air, challenging the strict host dependencies ruled for some oomycetes. Our findings further contribute to the understanding of oomycete ecosystem functioning in forest ecosystems

Selon le dernier rapport de l’EFSA-ECDC (EFSA Journal 2014), les parasites se classent en 8ème position des agents étiologiques impliqués dans les épidémies d’origine alimentaire reportées en 2012 en Europe. Par ailleurs, un récent rapport de l’OMS et la FAO (2014) classe Toxoplasma gondii en première position des parasites protozoaires à considérer dans le domaine alimentaire, suivi de Cryptosporidium spp et Giardia duodenalis. Les oocystes de T. gondii et Cryptosporidium spp et les kystes de G. duodenalis sont des formes très résistantes excrétées en très grande quantité dans les selles des individus malades. Lorsqu’ils se retrouvent dans l’environnement, ils peuvent y persister longtemps et contaminer certaines matrices alimentaires (végétaux et mollusques) lors de leur production primaire. A l’heure actuelle, en l’absence de méthodes d’analyse standardisées dans les aliments pour ces 3 parasites, peu de données de prévalence sont disponibles dans la littérature et les épidémies d’origine alimentaire restent négligées. Pour combler ce manque, une norme pour la détection/quantification des kystes de G. duodenalis et des oocystes de Cryptosporidium spp. dans les végétaux à feuilles vertes et fruits rouges à baies par microscopie à fluorescence est en cours de rédaction (ISO 18744). Des approches moléculaires, plus compatibles avec l’analyse de routine ont été développées par ACTALIA et l’équipe PROTAL pour détecter les 3 parasites simultanément sur des matrices végétales (Protofood, ANR-09-ALIA-009). Cependant, quelque soit la méthode de détection utilisée, elle met en évidence les parasites vivants et morts. Or, seul un parasite viable pourra être infectieux et donc potentiellement provoquer une maladie. A l’heure actuelle, les modèles in vivo constituent la méthode de choix pour évaluer l’infectiosité de manière précise, sensible et quantitative. Ils sont en revanche coûteux, lourds à mettre en œuvre et présentent un délai de réponse de plusieurs jours voire semaines qui n’est pas compatible avec les attentes des professionnels de l’agroalimentaire. L’objectif de la thèse est de développer des méthodes moléculaires pour caractériser la viabilité des 3 protozoaires dans des matrices alimentaires et disposer d’un outil permettant l’évaluation du risque lié à la détection de ces dangers dans les aliments. Ces méthodes seront comparées à celles qui permettent de mesurer l’infectiosité. Elles seront ensuite mises en œuvre pour évaluer leur potentiel pour déterminer l’efficacité d’inactivation de traitements technologiques sur des matrices alimentaires. / In the latest report from EFSA-ECDC (EFSA Journal 2014), parasites are ranked in the 8th position of the etiological agents involved in foodborne outbreaks reported in Europe in 2012. Moreover, in a recent report from the WHO and FAO (2014), Toxoplasma gondii is designated as the first protozoan parasite to be considered in the food domain, followed by Cryptosporidium spp. and Giardia duodenalis. Oocysts of T. gondii and Cryptosporidium spp., and cysts of G. duodenalis are excreted in big quantity by infected hosts and are particularly resistant. Consequently they can be found in the environment during long period and contaminate food matrices (vegetables and molluscs) during primary production. For now, since there are no standard methods to detect these 3 parasites in food samples, only few occurrence data are available and foodborne outbreaks remain neglected. To fill this gap, an ISO standard which describes a method for the detection and quantification of Cryptosporidium and Giardia in green leafy vegetables and red berries fruit by fluorescence microscopy is being draft (ISO 18744). Molecular approaches which are more suitable for routine analyses were developed by ACTALIA and PROTAL to simultaneously detect the 3 parasites in vegetable matrices (Protofood, ANR-09-ALIA-009). Nevertheless, whatever the used detection method, it highlights alive and dead parasites. But solely a living parasite can be infectious and induce pathology. For the moment, animal models are the favorite method to quantitatively evaluate infectivity with accuracy and sensitivity. However they are costly, heavy to implement and display a long time-to-result (from days to weeks) which does not fit with the agro-industrial needs. The objective of the thesis is to develop molecular methods to characterize the viability of the three protozoa in food matrices in order to have a tool allowing risk assessment in food safety. These methods will be compared to infectivity measurement methods. Then they will be implemented to evaluate their potential to determine the efficiency of technological treatments to inactivate protozoa in food matrices.

Mon étude a porté sur la spécificité de l'interaction entre deux protéines du parasite du paludisme (Plasmodium), tRip (tRNA import protein) et la tyrosyl-ARNt synthétase apicoplastique (api-TyrRS), avec l'ARN de transfert (ARNt). Plasmodium est un parasite intracellulaire qui conserve une organelle vestigiale, l’apicoplaste, qui possède son propre système de traduction. J’ai adapté la séquence de l’ARN messager pour produire l’api-TyrRS in vitro, et j’ai étudié la spécificité de la reconnaissance de l’ARNtTyr apicoplastique, qui évite les interactions erronées plutôt que de favoriser les correctes. La protéine tRip est située à la surface du parasite et est responsable de l’import des ARNt de l’hôte. Mes résultats suggèrent que cet import à lieu pendant la phase sanguine duparasite. Elle ne reconnait pas tous les ARNt de la même façon. Les modifications posttranscriptionnelles modulent l’affinité de tRip, et potentiellement, le taux d’import de cet ARNt. Finalement, j’ai identifié par SELEX une séquence nucléotidique qui se lie spécifiquement à tRip, un début pour la conception d'une molécule qui ciblerait spécifiquement le parasite du paludisme. / My study focused on the specificity of the interaction between two proteins of the malaria parasite (Plasmodium), tRip (tRNA import protein) and the apicoplastic tyrosyl-tRNA synthetase (api-TyrRS), with the transfer RNA (tRNA). Plasmodium is an intracellular parasite with a vestigial organelle, the apicoplast, which has its own translation system. The messenger RNA sequence was adapted to produce api-TyrRS in vitro, and I studied the specificity of apicoplastic tRNATyr recognition, which avoids erroneous interactions rather than favoring the correct ones. The tRip protein is located on the surface of the parasite, and is responsible for importing tRNAs from the host. My results suggest that this import takes place during the blood phase of the parasite. In addition, not all tRNAs are recognized uniformly. The post-transcriptional modifications of the tRNAs define the affinity of tRip, and potentialy, the import rate of this tRNA. Finally, I identified a short nucleotide sequence that binds specifically to tRip. It is a good starting point for designing a molecule that specifically targets the malaria parasite.

Une étude parasitaire de l'anguille d'Europe a été menée dans les lagunes de Biguglia et d'Urbino en Corse. La composition des communautés de parasites a été décrite. Treize espèces parasites ont été identifiées parmi lesquelles: trois digènes, Bucephalus anguillae, Deropristis inflata, Lecithochirium musculus; un monogène, Pseudodactylogyrus anguillae; trois cestodes, Bothriocephalus claviceps, Proteocephalus macrocephalus, Myzophyllobothrium sp. (larve); trois nématodes, Anguillicoloides crassus, Contracaecum sp. (larve enkystée), Goezia anguillae; un acanthocéphale, Acanthocephaloides incrassatus; un copépode, Ergasilus gibbus; et un myxozoaire, Myxobolus portucalensis. La présence d'espèces invasives, notamment le parasite branchial P. anguillae et le nématode parasite A. crassus, dans les lagunes corses est confirmée. Ces espèces, et particulièrement le monogène, présentent des valeurs épidémiologiques croissantes depuis les dernières études menées. Plusieurs espèces présentent des différences de prévalence significatives entre les deux lagunes. Des différences au niveau de la richesse spécifique et des valeurs de diversité, plus élevées pour les parasites des anguilles de la lagune d'Urbino au niveau intestinal métacommunautaire et infracommunautaire, ont été démontrées. Cependant les valeurs les plus élevées de diversité spécifique et les valeurs de dominance les plus basses ont été calculées pour les communautés parasitaires des anguilles de la lagune de Biguglia. Nous avons également mis en avant une diversité parasitaire spécifique plutôt faible chez les anguilles des lagunes corses par rapport aux autres lagunes d'Europe. Les communautés parasitaires de l'anguille d'Europe dans les lagunes de Biguglia et d'Urbino en Corse sont marquées par l'environnement de leur hôte. Une dépendance vis-à-vis de la salinité de la lagune a ainsi été démontrée. Les valeurs d'infestation les plus élevées ont été observées durant les saisons les plus chaudes de l'année pour la majorité des espèces parasites observées (B. anguillae, D. inflata, L. musculus, P. anguillae, P. macrocephalus, A. crassus, les kystes de Contracaecum sp., A. incrassatus et E. gibbus). Nous avons également démontré que l'état d'argenture et la taille ont une influence significative sur les taux d'infestation de sept espèces parasites (D. inflata, L. musculus, P. anguillae, P. macrocephalus, les kystes de Contracaecum sp., A. incrassatus et E. gibbus). La méthode de l'espèce indicatrice a confirmé que le site d'étude, la saison, l'état d'argenture ou la taille de l'anguille pouvait influer sur la présence de certaines espèces parasites. Le tégument de trois digènes parasites de l'anguille d'Europe, B. anguillae, L. musculus et D. inflata, a été étudié en microscopie électronique à balayage et à transmission. Nous avons démontré la présence de structures caractéristiques de l'organisation tégumentaire des digènes ainsi que de formations spécifiques, notamment au niveau de la structure des récepteurs sensoriels et des écailles. / A survey of the parasitic fauna of the European eel has been conducted in the Biguglia and Urbino lagoons in Corsica. The composition of the parasite communities was determined. Thirteen parasite species were identified namely: three digeneans, Bucephalus anguillae, Deropristis inflata, Lecithochirium musculus; one monogenean, Pseudodactylogyrus anguillae; three cestodes, Bothriocephalus claviceps, Proteocephalus macrocephalus, larvae of Myzophyllobothrium sp.; three nematodes, Anguillicoloides crassus, encysted larvae of Contracaecum sp., Goezia anguillae; one acanthocephalan, Acanthocephaloides incrassatus; one copepod, Ergasilus gibbus; and plasmodia of one myxozoan, Myxobolus portucalensis. The presence of invasive species in lagoons from Corsica, namely the gill monogenean P. anguillae and the swimbladder nematode A. crassus, was confirmed. These species, particularly the monogenean, exhibit increasing infection rates since the last studies conducted. Many species showed significant differences in prevalence between the two lagoons. Differences in the species richness and higher values of diversity for the intestinal parasite component communities and infracommunities of eels from the Urbino lagoon were demonstrated. However, highest values of richness and lowest dominance values were observed for the parasite communities of eels from the Biguglia lagoon. We also demonstrated lower values of diversity for the parasite communities of eels from Corsica in comparison to eels from other European lagoons. The environment of the host (in particular the salinity range) has been demonstrated to have a significant influence on the composition of the parasite communities of eels from the Biguglia and Urbino lagoons. Highest values of infestation were observed for the warmer seasons of the year for the majority of the parasite species (B. anguillae, D. inflata, L. musculus, P. anguillae, P. macrocephalus, A. crassus, encysted larvae of Contracaecum sp., A. incrassatus, and E. gibbus). We also demonstrated that silvering stage and length have a significant influence on the rates of infestation by seven parasite species (D. inflata, L. musculus, P. anguillae, P. macrocephalus, cysts of Contracaecum sp., A. incrassatus et E. gibbus). The indicator species method confirmed the assumption that site sampling, season, silvering stage and length of the eel could have an influence on the presence of parasite species. The teguments of three digeneans (B. anguillae, L. musculus and D. inflata) recovered within the European eel were studied using scanning and transmission electron microscopy. We showed the presence of structures characteristic of the tegumental organization of digeneans but also the presence of specific structures such as various types of sensory receptors and spines.