Migrationsverhalten von Toxocara-Larven und resultierende Transkriptregulation im Zuge der Toxocara-Infektion des paratenischen Wirtes

Toxocara canis and T. cati are worldwide occurring roundworms of dogs and cats with a high zoonotic potential. Migrating larvae of T. canis in paratenic hosts, including humans, exhibit a strong affinity to the CNS and may cause neurotoxocarosis accompanied by a variety of neurological symptoms. T. cati larvae have been rarely found in nervous tissues, therefore, T. canis larvae are considered the causative agents of human neurotoxocarosis. However, direct comparison of previously published studies is not feasible as larval migration is influenced by a variety of factors like mouse strains and inoculation doses. Additionally, pathomechanisms of T. canis or T. cati induced neurotoxocarosis as well as host reactions towards the respective parasite have not been sufficiently examined. The present study aimed to directly compare T. canis and T. cati larval migration behaviour in the mouse as model for paratenic hosts with focus on the central nervous system (CNS) during the course of infection. Furthermore, microarray analysis of infected mouse brains was conducted to provide data on the molecular level for the characterization of host reactions towards T. canis- or T. cati-infection and to possibly elucidate underlying pathomechanisms. Microarray data also allows identification of differences between T. canis- and T. cati-infections on transcriptional level. For the examination of larval migration, C57Bl/6J (B6) mice were infected with 2000 embryonated T. canis and T. cati eggs, respectively. Additionally, Balb/c mice were infected with T. cati eggs. Obtained organs were microscopically examined to determine presence of larvae at eight time points post infectionem (pi). The main focus was put on the CNS which included analysis of larval distribution in cerebra and cerebella (divided in right and left hemispheres), spinal cord and eyes. Histopathological analysis of brains of all infection groups was conducted to characterize neurostructural damage. For microarray analysis, B6 mice were infected as described. Cerebra as well as cerebella were obtained day 42 pi and processed for further analysis. Significant differences in larval distribution were observed between and within the infection groups during the course of infection. Recovery rates of T. canis in the brain were significantly higher than those of T. cati larvae. Surprisingly, T. canis larvae were significantly more frequently found in cerebra of infected mice, whereas T. cati showed a preference to cerebella. Structural damage in brain tissue was most severe in T. canis-infected mice, even though observed in all infection groups during the course of infection. Microarray analysis underlined these differences and resulted in more differentially transcribed genes (DTGs) for T. canis- than T. cati-infected brains. A strong immune reaction in terms of up-regulated immune associated genes was observed in both infection groups with the most prominent up-regulation observed in T. canis-infected brains. Additionally, genes associated with the Gene Ontology (GO) terms “sensory perception” as well as “behaviour/taxis” were significantly enriched. In contrast, significant enrichment of the biological module “lipid/cholesterol biosynthetic process” was observed in down-regulated genes of T. canis-infected brain regions. Cholesterol is a highly abundant component of the brain and has been assigned to several functions. Dysfunction of cholesterol synthesis and resulting concentration changes may lead to disturbances in signal transduction or even neurodegenerative disease. Direct comparison of transcriptional changes revealed only minor DTG overlap between brains of T. canis- and T. cati-infected mice. This demonstrates major differences in gene regulation between the infection groups, additionally underlining the evident differences between T. canis and T. cati larval behaviour as observed previously on a molecular level. Overall, obtained data provides insights into T. canis and T. cati induced neurotoxocarosis in terms of larval behaviour within the paratenic host as well as the host’s reaction towards migrating or arrested larvae in the brain on a transcriptional level. Even though to a lesser extent than T. canis, T. cati larvae are able to cause structural damage and provoke a well detectable host reaction towards migrating larvae. Therefore, T. cati should not be underestimated as a zoonotic agent. Microarray data delivers a comprehensive basis for future analyses over the course of infection as well as functional tests to identify gene regulatory circuits that are crucial for pathogenesis of neurotoxocarosis. Such further analyses will allow a detailed characterization of the pathogenesis of neurotoxocarosis and help to identify potential therapeutic targets.