Las infecciones parasitarias entéricas constituyen un problema sanitario muy común entre losanimales de granja y, debido al potencial zoonótico de algunos parásitos, el contacto con losespecímenes infectados puede causar enfermedades en los seres humanos. En Misión Nueva Pompeya (MNP) Chaco, existen condiciones de saneamiento ambiental deriesgo para las comunidades Wichí que allí habitan. Las lagunas constituyen la principal fuentede abastecimiento de agua y, dado que son además, abrevaderos para los animales silvestres,domésticos y ganado, soportan el aflujo de excretas las cuales son arrastradas por acción eólicay pluvial. Un relevamiento epidemiológico en la región indicó que el 92% de los niños Wichíspadece enteroparasitosis transmitidas por el agua. Para determinar si existe riesgo detransmisión zoonótica de protozoosis en MNP, se desarrollaron PCRs diagnósticas y unamembrana de hibridización reversa en línea para la identificación de los protozoarios. Seidentificaron en heces animales Entamoeba bovis, Entamoeba polecki y Balantidium coli. Estasúltimas fueron también halladas en heces de niños residentes de MNP. Los cerdos presentaronmayor diversidad de parásitos. Por otra parte, Entamoeba histolytica es el agente causal de amebiasis intestinal. Estudios handemostrado que contiene elementos repetitivos en su genoma: LINEs y SINEs y los Elementos Repetitivos Específicos de Entamoeba: ERE2. Este trabajo mostró que los elementos LINE sonmás abundantes que ERE2 y SINE (1879, 1268 y 867, respectivamente). El 25,9% de los genes de E. histolytica están próximos a estos elementos. Las funciones moleculares de estos genes fueronestablecidas por medio de la Ontología Génica. Se determinaron 7 funciones moleculares, todascon posibles contribuciones a mecanismos de patogenicidad: Unión a GTP, Actividad tipocisteína peptidasa, Actividad oxidoreductasa, Actividad Nucleosido-trifosfatasa, Actividad ATPasa y Actividad 2-alkenal reductasa. 6 se encontraban asociadas a los elementos repetitivosespecíficos de Entamoeba (ERE2), 3 a LINE y 3 a SINE. El algoritmo de análisis in sillico desarrollado permitió obtener genes candidatos para validarsecomo genes implicados en mecanismos de patogenicidad. Mediante ensayos de silenciamientopor ARN interferente se obtuvieron trofozoítos silenciados transitorios para el gen Cisteínaproteinasa. Ensayos funcionales indicaron una disminución en la eritrofagocitosis y en el dañocelular. Esto demuestra que existiría una relación entre ERE2, y los diferentes estados devirulencia del parásito ya que los genes aledaños (potencialmente susceptibles a la modulaciónpor estos ETs)codifican para proteínas con posibles contribuciones a mecanismos depatogenicidad. Enteric parasitic infections are a very common health problem among farm and domesticanimals because many of them can cause several diseases in humans. The infection can beacquired through the ingestion of parasite infective stages contained in feces, thus, the contactwith animals, soil or consumption of vegetables and water contaminated with infected fecespresent health hazards. Misión Nueva Pompeya is located in the northwest of the Province of Chaco. In this place, theenvironmental sanitary conditions are a risk factor to rural Wichí communities that live there. The lagoons are the main source of water supply of lakeshore communities and also they aretroughs for wildlife, pets and livestock. Moreover, they support the flow of excreta carried bywind and rain action. In such a scenario, the direct consequence is the serious watercontamination with bacteria, protozoa and helminths. In order to establish if there is a risk ofzoonotic transmission of protozoosis, it was necessary to develop molecular diagnostic tools: PCRs and RLBH (Reverse Line Blot Hybridization). These tools allowed to identifyunequivocally the presence of Entamoeba bovis, Entamoeba polecki and Balantidium coli. Thehighest diversity of protozoan parasites was found in pigs. Moreover, Entamoeba histolytica is the causative agent of intestinal amebiasis. This parasitemainly affects humans. The infection is acquired by the ingestion of cysts; once these cysts areingested, they excyst in the gut releasing the trophozoites. There are mechanisms that allowtrophozoites to invade and survive in the host: the ability to adhere to the intestinal epithelium,the cytotoxic capacity and the ability to engulf host cells. At present, studies have shown that E.histolytica contain a large repertoire of repetitive elements (transposable elements, TEs) thatconsist in non-Long Terminal Repeats retrotransposons: Long and Short Interspersed Elements (LINEs and SINEs) and Entamoeba Repetitive Element (ERE2). These transposable elements (TE) can give rise to the appearance of different virulent phenotypes by changing the expressionof adjacent genes. In this context, our goal was to analyze the distribution of TE in the genomeof E. histolytica HM-1: IMSS and to assess their impact on the expression of near genes involvedin pathogenicity mechanisms. To analyze the distribution of TEs, we run the Repeat Masker software using the E. histolyticagenome and a database containing all its reported TEs (SINE, LINE1 and ERE2). Subsequently,to display the annotation and the TEs we used the free software ARTEMIS. To estimate thepotential impact of TEs on gene expression we performed a functional categorization ofassociated genes based on GO (Gene Ontology) terms, in order to reveal the relation of the TEinsertions with functional categories. The mapping of TEs showed that the abundance of LINEs was greater than that of SINEs and ERE2 (1879, 1268 y 867 copies, respectively). GTP binding, Rab GTPase activator activity, Cysteine-type peptidase activity, Oxidoreductase activity, ATPase activity, Nucleosidetriphosphataseactivity and 2-alkenal reductase [NAD(P)] activity were the molecular functionsfound to be statistically significant. This analysis revealed that ERE2 is the TE with morecategories of molecular functions associated (6 out of 7), while LINE and SINE are in associationwith 3 categories only. In order to validate that certain genes found near of TEs, are involved in the virulence of theparasite, candidate genes were selected and silencing assays were performed using thetechnique of RNA interference. In order to evaluate its effect on the phenotype of E. histolytica HM1:IMMS, in vitro virulence assays were performed. Fil: López Arias, Ludmila Sol. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.