Blastocystis sp. é um protozoário intestinal comumente encontrado em amostras fecais de muitas espécies animais, incluindo humanos, sendo pouco estudado em pacientes imunocomprometidos, especialmente nos candidatos a transplante. O objetivo do presente estudo foi avaliar a ocorrência e a identificação molecular de subtipos (ST) de Blastocystis sp. em amostras fecais de pacientes candidatos a transplante. A Reação em Cadeia da Polimerase foi realizada utilizando primers específicos para o DNA ribossomal de Blastocystis. As sequências de DNA obtidas foram alinhadas e comparadas com outras sequências do banco de dados GenBank e MLST (Multilocus Sequence Typing). As amostras analisadas mostraram uma positividade de 16% (24/150) para Blastocystis sp. A maior ocorrência foi observada em candidatos a transplante renal (31,4%), seguida de candidatos a transplante hepático (10,4%) e candidatos a transplante de medula óssea (5,9%). O ST3 (45,8%) foi o mais prevalente entre os isolados, seguido pelo ST1 (37,5%), ST2 (12,5%) e ST7 (4,2%). Foi observado dentro dos subtipos: os alelos 4 e 78/81 (ST1); alelos 11 e 12 (ST2); alelos 34, 36, 37 e 54 (ST3) e alelo 96 (ST7). Este é o primeiro estudo de identificação molecular de Blastocystis sp. em candidatos a transplante. Os presentes resultados confirmam a maior ocorrência do subtipo 3 em candidatos a transplante, além de reforçar a importância de novas investigações de Blastocystis sp. nesses pacientes. / Blastocystis sp. is an intestinal protozoan commonly found in faecal samples of many animal species, including humans, but poorly studied in immunocompromised patients, especially in transplant candidates. The purpose this study was to evaluated the occurrence and molecular identification of Blastocystis sp. in faecal samples from transplant candidate patients. The Polymerase Chain Reaction was performed using specific primers for Blastocystis DNA ribosomal. The DNA sequences obtained were aligned and compared with other sequences from the GenBank and MLST database. The analyzed samples showed a positivity of 16% (24/150) for Blastocystis sp. The highest occurrence was observed in renal transplant candidates (31.4%), followed by hepatic transplant candidates (10.4%) and candidates for bone marrow transplantation (5.9%). The ST3 (45.8%) was the most prevalent among the isolates followed by ST1 (37.5%), ST2 (12.5%) and ST7 (4.2%). It was observed within the subtypes: alleles 4 and 78/81 (ST1); alleles 11 and 12 (ST2); alleles 34, 36, 37 and 54 (ST3); and allele 96 (ST7).This is the first study of Blastocystis sp. molecular identification in transplant candidates. These results confirmed the highest occurrence of the subtype 3 in transplant candidates, as well as reinforcing the importance of the new investigation of Blastocystis sp. in these patients.

Blastocystis sp. é um protozoário comumente encontrado em amostras fecais de humanos e animais, envolto por aspectos patogênicos e zoonóticos ainda controversos. Estudos recentes têm demonstrado a distribuição dos subtipos (STs) de Blastocystis sp., porém são escassos os relatos sobre a sua caracterização molecular na América Latina, sobretudo no Brasil. O objetivo do presente estudo foi investigar os STs presentes em isolados fecais de indivíduos acompanhados no Hospital das Clínicas de São Paulo da Faculdade de Medicina da Universidade de São Paulo (HC/FMUSP). Para tanto, amostras fecais positivas para Blastocystis sp. diagnosticadas na Seção de Parasitologia do Laboratório Central (HC/FMUSP) foram utilizadas para o isolamento de DNA. A reação em cadeia da polimerase (PCR) foi realizada utilizando iniciadores específicos para a subunidade 18S do DNA ribossomal de Blastocystis sp. A reação de sequenciamento dos produtos de PCR foi realizada, as sequências de DNA obtidas foram alinhadas e comparadas com outras sequências da base de dados GenBank e MLST. Foram identificados os STs (ST1, ST2, ST3 e ST6), sendo o ST3 o mais prevalente entre os isolados humanos seguido pelo ST1. Os alelos de número 34 e 36 foram os mais frequentes. Em conclusão, estes resultados contribuem para a caracterização molecular e a distribuição dos STs de Blastocystis sp. em amostras de fezes humanas no Brasil. / Blastocystis sp. is an organism described as enteroparasite protozoan, commonly found in stool samples from humans. Several subtypes have been described in humans, but pathogenic potential and aspects epidemiological are still controversial. The aim of the present study was to investigate Blastocystis subtypes (STs) from patients of Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo (HC/FMUSP), Brazil. Blastocystis sp. positive stool samples diagnosed in Section of Parasitology of Central Laboratory (HC/FMUSP) were used for DNA isolation. Polymerase chain reaction (PCR) was performed using specific primers targeting the small subunit of rRNA gene. Direct DNA sequencing of PCR products was performed, and the DNA sequences were aligned and compared to other sequences present in GenBank and MLST database. Four STs were identified (ST1, ST2, ST3 and ST6), where the ST3 was the most prevalent ST among human isolates followed by ST1. Allele nos. 34 and 36 were the most frequent. Another important finding is the presence of ST6, rarely detected in human isolates. In conclusion, our results contribute to the molecular characterization and distribution of Blastocystis sp. STs in human stool specimens in Brazil.

Blastocystis sp. é um protozoário comumente encontrado em amostras fecais de humanos e animais, envolto por aspectos patogênicos e zoonóticos ainda controversos. Estudos recentes têm demonstrado a distribuição dos subtipos (STs) de Blastocystis sp., porém são escassos os relatos sobre a sua caracterização molecular na América Latina, sobretudo no Brasil. O objetivo do presente estudo foi investigar os STs presentes em isolados fecais de indivíduos acompanhados no Hospital das Clínicas de São Paulo da Faculdade de Medicina da Universidade de São Paulo (HC/FMUSP). Para tanto, amostras fecais positivas para Blastocystis sp. diagnosticadas na Seção de Parasitologia do Laboratório Central (HC/FMUSP) foram utilizadas para o isolamento de DNA. A reação em cadeia da polimerase (PCR) foi realizada utilizando iniciadores específicos para a subunidade 18S do DNA ribossomal de Blastocystis sp. A reação de sequenciamento dos produtos de PCR foi realizada, as sequências de DNA obtidas foram alinhadas e comparadas com outras sequências da base de dados GenBank e MLST. Foram identificados os STs (ST1, ST2, ST3 e ST6), sendo o ST3 o mais prevalente entre os isolados humanos seguido pelo ST1. Os alelos de número 34 e 36 foram os mais frequentes. Em conclusão, estes resultados contribuem para a caracterização molecular e a distribuição dos STs de Blastocystis sp. em amostras de fezes humanas no Brasil. / Blastocystis sp. is an organism described as enteroparasite protozoan, commonly found in stool samples from humans. Several subtypes have been described in humans, but pathogenic potential and aspects epidemiological are still controversial. The aim of the present study was to investigate Blastocystis subtypes (STs) from patients of Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo (HC/FMUSP), Brazil. Blastocystis sp. positive stool samples diagnosed in Section of Parasitology of Central Laboratory (HC/FMUSP) were used for DNA isolation. Polymerase chain reaction (PCR) was performed using specific primers targeting the small subunit of rRNA gene. Direct DNA sequencing of PCR products was performed, and the DNA sequences were aligned and compared to other sequences present in GenBank and MLST database. Four STs were identified (ST1, ST2, ST3 and ST6), where the ST3 was the most prevalent ST among human isolates followed by ST1. Allele nos. 34 and 36 were the most frequent. Another important finding is the presence of ST6, rarely detected in human isolates. In conclusion, our results contribute to the molecular characterization and distribution of Blastocystis sp. STs in human stool specimens in Brazil.

Blastocystis is an obligately anaerobic protist, commonly found in intestinal tract of numerous animals and humans across whole world. It is genetically very variable and rather enigmatic organism. Many aspects of its biology need to be further studied and clarified. On a chosen farm were during the year 2010 collected samples of pig faeces for parasitological survey. A total number of 40 samples was collected and cultivated by the method of Dobel-Leidlaw (1926). Of them, 19 was positive for Blastocystis. Other samples were checked by molecular methods (PCR). Using them, five Blastocystis sequences were obtained, which clearly belong to subtypes 1 and 5.

Objetivo: Determinar la prevalencia de infección por Strongyloides stercolaris y otras enteroparasitosis en el pueblo joven Santo Toribio de Mogrovejo de Chiclayo durante Junio-Octubre del 2011. Material y Métodos: Estudio descriptivo, trasversal; muestreo aleatorio, estratificado, polietápico, siendo el tamaño muestral de 106 pobladores. Se diseñó y validó una ficha de recolección epidemiológica. Un biólogo recibió entrenamiento en las técnicas de diagnóstico de Strongyloides stercolaris en un centro referencial de Lima. Se recolectaron 3 muestras por paciente, sometidas a 5 técnicas parasitológicas: Examen directo de heces, Baermann modificado en Copa por Lumbreras, Test de sedimentación espontánea, Cultivo en agar y Cultivo Dancescu. Resultados: Se visitaron 124 casas; el porcentaje de respuesta fue de 85,7%. Se logró entrevistar 106 personas. El promedio de edad fue de 27,8 +/- 16,9 años; hubieron 31 hombres (29,2%) y 75 mujeres (70,8%). El 26,4% de personas habían realizado un viaje a la Sierra y/o Selva en los últimos 5 años con una estancia mayor a un mes. El piso de tierra fue el más frecuente en el total de viviendas (55,6%); 102 personas (96,2 %) tenían desagüe; 23 pobladores (21,7 %) tuvieron al menos un parásito detectado. No se hallaron pobladores infectados con Strongyloides stercolaris. La enteroparasitosis más frecuente fue por protozoarios, con predominio de Blastocystis hominis en un 12,3%. Conclusiones: Se halló una baja frecuencia de enteroparasitosis y ausencia de pobladores infectados con Strongyloides stercolaris. El parásito más frecuente fue Blastocystis hominis. / Tesis

Objetivo: Determinar la prevalencia de infección por Strongyloides stercolaris y otras enteroparasitosis en el pueblo joven Santo Toribio de Mogrovejo de Chiclayo durante Junio-Octubre del 2011. Material y Métodos: Estudio descriptivo, trasversal; muestreo aleatorio, estratificado, polietápico, siendo el tamaño muestral de 106 pobladores. Se diseñó y validó una ficha de recolección epidemiológica. Un biólogo recibió entrenamiento en las técnicas de diagnóstico de Strongyloides stercolaris en un centro referencial de Lima. Se recolectaron 3 muestras por paciente, sometidas a 5 técnicas parasitológicas: Examen directo de heces, Baermann modificado en Copa por Lumbreras, Test de sedimentación espontánea, Cultivo en agar y Cultivo Dancescu. Resultados: Se visitaron 124 casas; el porcentaje de respuesta fue de 85,7%. Se logró entrevistar 106 personas. El promedio de edad fue de 27,8 +/- 16,9 años; hubieron 31 hombres (29,2%) y 75 mujeres (70,8%). El 26,4% de personas habían realizado un viaje a la Sierra y/o Selva en los últimos 5 años con una estancia mayor a un mes. El piso de tierra fue el más frecuente en el total de viviendas (55,6%); 102 personas (96,2 %) tenían desagüe; 23 pobladores (21,7 %) tuvieron al menos un parásito detectado. No se hallaron pobladores infectados con Strongyloides stercolaris. La enteroparasitosis más frecuente fue por protozoarios, con predominio de Blastocystis hominis en un 12,3%. Conclusiones: Se halló una baja frecuencia de enteroparasitosis y ausencia de pobladores infectados con Strongyloides stercolaris. El parásito más frecuente fue Blastocystis hominis.

During 2010, faeces samples for parasitology research oriented on Blastocystis were collected from an anonymous farm. A total of 55 samples were collected (of them for 10 faeces samples from hens, ducks and geese and 25 from pigeons). The samples were cultured in Dobell-Leidlaw medium and viewed by light microscopy. However, this method led to only two foundings of Blastocystis (one from hen, the other from pigeon). Thus, PCR and nested-PCR with specific primers were later used for better detection of Blastocystis. The samples for PCR detection were not collected from the aforementioned farm, but they originated from a collection of isolated DNA samples that was available on the Parasitology institute of AS CR. The results of PCR were checked after electrophoresis and verified by sequenation. The obtained sequences of bird-isolated Blastocystis were phylogenetically analysed and as described to subtype 7.

Blastocystis is an anaerobic single-celled protozoan that commonly occurs in the intestinal tract of animals and humans. It is a genetically very variable organism. Blastocystis can be found both in healthy specimens and in patients with gastrointestinal disorders. In 2011/2012, I examinated already isolated DNA samples from domestic and wild pigs by molecular methods in the laboratory of the ASCR Parasitology Institute. In total, 110 samples were examined. The domestic pigs were positive in 91 % (51/56) and wild pigs in 67 % (36/54). The overall prevalence of domestic pigs was higher by 24 %. Several sequences of SSU rRNA gene obtained during the work suggest that pigs may serve as host for atypical Blastocystis subtypes.

Blastocystis est un protozoaire anaérobie trouvé dans le tube digestif de l’homme et de nombreux animaux. Il est à ce jour le parasite intestinal le plus fréquemment retrouvé dans les selles humaines. Dix-sept sous-types (ST1 à ST17) ont été décrits en se basant sur la comparaison des séquences du gène de l’ARNr 18S. L’infection à Blastocystis est associée à une variété de troubles gastro-intestinaux et plusieurs études suggèrent une corrélation entre la pathogénicité et le ST du parasite. Trois différents axes de recherche ont été développés. Le premier s’est focalisé sur la prévalence et la biodiversité génétique de ce parasite dans les populations humaines. Des études épidémiologiques ont été menées en France et au Liban mais aussi en Afrique en réalisant la première enquête au Sénégal. Le sous-typage des isolats a été réalisé par PCR en temps réel en ciblant un domaine du gène de l’ARNr 18S suivi d’un séquençage direct du produit de PCR. Au Liban, la prévalence de Blastocystis était de 20% dans la population globale avec une corrélation entre le ST1 et le développement de symptômes gastro-intestinaux. Dans le même pays, cette prévalence dépassait les 60% chez des patients symptomatiques et des écoliers. Au Sénégal, la prévalence observée est la plus importante jamais décrite pour ce parasite puisqu’elle atteignait 100% dans une population d’une centaine d’enfants vivant en milieu rural. Ces données soulignent l’impact socioéconomique de la blastocystose dans les pays en développement où les conditions sanitaires sont souvent précaires. En France, une prévalence importante de 18% a pourtant été observée dans une large étude épidémiologique englobant des patients présentant ou non des symptômes et suivis dans 11 hôpitaux répartis sur tout le territoire français. Le ST3 est prédominant suivi des STs 1, 2 et 4 comme dans une majorité de pays à travers le monde. Le deuxième axe s’est concentré sur l’identification des facteurs de risque de transmission de Blastocystis à l’homme. Le parasite a été recherché dans les selles de vaches et de patients ainsi que dans des échantillons d’eau consommée par l’homme et les animaux dans une région géographique limitée du Nord Liban. 30% des échantillons humains, 69% des échantillons d'eau et 80% des échantillons de bovins étaient positifs pour le parasite. Le ST3 était prédominant dans les échantillons humains et d’eau suivi des ST1, ST2 et ST4. Par contre, ST10 et ST14 étaient prédominants chez les bovins mais ces deux STs n’ont pas été retrouvés dans les autres types d’échantillons. Pour expliquer l'absence des ST10 et ST14 dans ces échantillons, une transmission de ces STs par contact direct entre les bovins et/ou l'absence de formes kystiques transmissibles pour ces STs ont été proposées. Ce parasite a aussi été recherché dans les selles de nombreux groupes d’animaux du zoo de La Palmyre en France. Nous avons montré que près de 40% des selles analysés étaient positives pour Blastocystis et identifié de nouveaux réservoirs d'infections pour l’homme chez les carnivores. La prévalence du parasite atteignait 60% chez les primates chez lesquels les ST1 à ST5 identifiés sont identiques à ceux observés chez l'homme confirmant la faible spécificité d’hôte de ces STs. Dans une autre étude, la prévalence de Blastocystis était de seulement 3,5% dans une population de chiens en France suggérant que cet animal n'est pas un hôte naturel de Blastocystis. Enfin, pour clarifier la pathogénicité de ce parasite, le troisième axe de mes travaux a souligné le caractère invasif de Blastocystis dans un cas de péritonite appendiculaire chez une fillette de 9 ans de retour du Maroc. Seul Blastocystis a été détecté dans les selles, l’appendice, le liquide péritonéal et le sac de Douglas de cette patiente. Une gastro-entérite s’est de plus déclarée simultanément chez 26 membres de la famille de l'enfant suggérant une épidémie qui pourrait trouver son origine dans la consommation commune d’une eau contaminée. / Blastocystis sp. is an anaerobic parasitic protozoa found in the digestive tract of humans and numerous animals. To date, it is the most common intestinal parasite found in human feces with worldwide distribution. Seventeen subtypes (ST1-ST17) have been described based on the comparison of SSU rRNA gene sequences. Blastocystis infection is associated with various gastrointestinal disorders and many studies suggest a correlation between Blastocystis STs and pathogenicity. My work was developed on three different topics. The first concerned the prevalence and the genetic biodiversity of the parasite in human populations. Epidemiological studies were conducted in France and Lebanon but also in Africa by performing the first survey of this parasite in Senegal. Subtyping of the isolates was performed by real-time PCR targeting a domain of the SSU rRNA gene followed by direct sequencing of the PCR product. In Lebanon, the prevalence of Blastocystis reached 20% in the general population and we demonstrated a correlation between ST1 infection and the presence of symptoms. In the same country, this prevalence was 60% in schoolchildren and patients presenting gastrointestinal symptoms. Strikingly, the prevalence of Blastocystis in a population of one hundred children living in a rural area reached 100% in Senegal and more than half of the infected children by the parasite presented gastrointestinal disorders. These latter studies highlighted the socioeconomic impact of blastocystosis in developing countries with poor hygiene sanitation. In France, a large-scale molecular epidemiological study was performed including patients presenting or not gastrointestinal symptoms. Stool samples were collected during winter and summer in 11 hospitals spread all over the French territory. We observed a high prevalence of Blastocystis in the french population with an average of 18.2% and the predominance of ST3 followed by ST1, ST4 and ST2 as in numerous countries. We also identified seasonal variations since the average prevalence of the parasite is 13.6% in winter and 23.1% in summer. The second topic focused on the identification of the risk factors of Blastocystis transmission to humans. We searched this parasite in bovid and human stools as well as in drinking water samples consumed by bovids and breeders in a limited geographic area of North-Lebanon. 30% of human samples, 69% of water samples and 80% of bovid samples were positive for the parasite. Interestingly ST3 is predominant in human and water samples followed by ST1, ST2 and ST4. ST10 and ST14 were predominant in bovid but both STs are lacking in human and water samples. To explain the lack of ST10 and ST14 in human and water samples, we suggested a transmission of these STs occurring through direct contact between bovid and / or the absence of transmissible cystic forms of these STs. Furthermore, this parasite was searched in the stools of numerous animal groups in the zoo of La Palmyre in France. We showed that nearly 40% of the analyzed stools were positive for Blastocystis and identified new reservoirs of human infections in carnivores. The prevalence of the parasite reached 60% in primates in which the identified ST1 to ST5 are identical to those observed in humans confirming the limited host specificity of these STs. In another study, we showed that the prevalence of Blastocystis was of only 3.5% in a population of one hundred dogs in France suggesting that this pet is not a natural host of Blastocystis. Finally, to clarify the pathogenicity of this parasite, the third topic highlighted the invasive character of Blastocystis observed in a case of appendicular peritonitis in a 9-year old girl returning from Morocco. Only Blastocystis was detected in stools, appendix, peritoneal liquid and Douglas pouch of the patient. Interestingly, simultaneous gastroenteritis occurred in 26 members of the child’s family suggested an outbreak with contaminated water as probable origin.

Les douleurs abdominales chroniques, souvent associées à une hypersensibilité viscérale d’origine colique (HSVC), sont l’un des symptômes majeurs constatés lors du syndrome de l’intestin irritable (SII). Le SII est une colopathie chronique fonctionnelle touchant environ 11% de la population mondiale et altérant significativement la qualité de vie des patients. L’étiologie multifactorielle de cette pathologie rend la physiopathologie complexe. Les gastroentérites infectieuses ont été décrites comme l’un des facteurs de risque dans le développement du SII-post-infectieux (SII-PI). Le SII-PI survient en effet dans 4 à 31% des cas suite à une gastroentérite aigüe d’origine bactérienne, virale ou parasitaire. Ces infections peuvent avoir de nombreuses répercussions et en particulier sur l’intégrité de la barrière épithéliale intestinale, le système immunitaire ou encore sur le microbiote intestinal. Par ailleurs, suite à une infection parasitaire, le risque de développer un SII est de 40% contre seulement 14% suite à une infection bactérienne.Blastocystis est le parasite intestinal le plus fréquemment retrouvé chez l’Homme. Néanmoins, malgré de récentes études épidémiologiques rapportant une plus forte prévalence de ce parasite chez les patients atteints de SII, son rôle en santé humaine reste débattu. De plus, d’autres études rapportent que les individus porteurs de ce parasite présentent des douleurs abdominales et sont atteints d’une dysbiose intestinale. Actuellement, l’absence d’un modèle animal d’infection par Blastocystis reproductible ne permet pas d’étudier les mécanismes physiopathologiques liés à l’infection et donc d’explorer la contribution éventuelle de ce parasite dans le SII.Les objectifs de ce travail de thèse étaient tout d’abord de mettre en place un modèle murin d’infection expérimentale par Blastocystis pour dans un deuxième temps évaluer si ce parasite est capable d’induire une HSVC et une dysbiose intestinale avec l’objectif d’établir un nouveau modèle de SII d’origine infectieuse chez le rat. Pour répondre au premier objectif, le pouvoir infectieux de différents sous-types et différentes formes du parasite (formes vacuolaires ou kystes), isolés de cultures axéniques ou purifiés à partir de selles de patients et d’animaux a été évalué chez des animaux de laboratoire (rats et souris). Nous avons ainsi réussi à établir un modèle reproductible d’infection chronique par Blastocystis chez le rat de laboratoire à l’aide de kystes purifiés à partir de selles humaines.L’utilisation de ce modèle in vivo, nous a permis de mettre en évidence que le sous-type 4 (ST4) de Blastocystis induit une HSVC sans origine inflammatoire chez les rats expérimentalement infectés. De plus, les animaux développent un comportement type anxio-dépressif corrélé à l’HSVC. La dysbiose intestinale associée à l’infection se caractérise par une augmentation de la richesse bactérienne et une diminution du ratio Firmicutes/Bacteroidetes. Par ailleurs, nous avons corrélé l’HSVC à l’augmentation de l’abondance relative du genre Bacteroides et la diminution de l’abondance relative de la famille des Clostridiaceae, bactéries productrices d’acides gras à chaine courte (AGCC). Une diminution des taux d’AGCC fécaux a d’ailleurs été constatée chez les rats infectés. De plus, nous avons mis en évidence une augmentation de l’activité de protéases à sérine dans les fèces des animaux infectés pouvant expliquer l’HSVC.Ces données suggèrent qu’une infection gastro-intestinale par Blastocystis serait associée à une hypersensibilité viscérale d’origine colique (HSVC) et à un déséquilibre de la flore intestinale (dysbiose). Ainsi, ce nouveau modèle d’infection pourrait être un bon modèle de SII d’origine infectieuse et pourrait donc contribuer à un meilleur diagnostic et au développement de nouvelles stratégies thérapeutiques pour des pathologies chroniques de l’intestin chez certains individus. / Chronic abdominal pain often associated with colonic hypersensitivity (CHS) is one of the major symptoms of irritable bowel syndrome (IBS). IBS is a functional chronic disorder affecting ~11% of worldwide population and disturbing patients’ quality of life. Etiology is multifactorial and thus pathophysiology is complex and remains poorly understood. Infectious gastroenteritis has been described as one of the risk factors for development of post-infectious IBS (PI-IBS). PI-IBS can occur in 4-31% of patients following acute gastroenteritis of bacterial, viral or parasitic origin. Numerous studies support a role for pathogen-mediated modifications in the resident intestinal microbiota, epithelial barrier integrity and immune activation in PI-IBS. Interestingly, the risk of IBS is highest with protozoal enteritis, with ~40% of individuals developing IBS against ~14% following bacterial infection. Blastocystis is the most common intestinal parasite found in human intestinal tract. Nevertheless, clinical relevance remains controversial, despite recent epidemiological studies showing a higher prevalence of this parasite in IBS patients. Interestingly, studies report that individuals carrying Blastocystis display abdominal pain and intestinal dysbiosis. Currently, the lack of reproducible animal model of Blastocystis infection does not allow to study the pathological mechanisms related to infection and thus to explore the potential contribution of this parasite in IBS.The aims of this study were first to develop a murine model of Blastocystis infection and then to investigate whether this parasite could lead to the development of intestinal dysbiosis associated CHS with the aim of developing a new PI-IBS rat model.The first aim was to evaluate the infectivity of different parasitic subtypes and stages (vacuolar and cystic forms) isolated from axenic cultures or purified from human or animal feces, into laboratory animals (rats and mice). Interestingly, we succeeded in the development of a reproducible model of chronic infection by Blastocystis in laboratory rats using cysts purified from human stool.Using this animal model, we found that Blastocystis ST4 induced non inflammatory CHS in infected rats. In addition infected rats developed anxiety- and depressive-like behavior correlated with CHS. Infection associated intestinal dysbiosis was characterized by increased bacterial richness and decreased Firmicutes/Bacteroidetes ratio. Interestingly, we correlated CHS with the increase in the relative abundance of genus Bacteroides and the decrease in the relative abundance of the family Clostridiaceae, some bacteria producing Short Chain Fatty Acids (SCFAs). Indeed, fecal SCFAs levels were decreased in infected rats. These decreases were correlated with the relative abundance of genus Oscillospira which was also described increased in Blastocystis individual carriers. In addition, we have demonstrated an increase in fecal serine protease activity in infected animals that may explain development of CHS.These data suggest that a gastrointestinal infection with Blastocystis may be associated with the establishment of intestinal dysbiosis associated CHS. Thus, this new infectious model could be a good model of PI-IBS and could therefore contribute to a better diagnosis and development of new therapeutic strategies for chronic bowel diseases.