Eimeriosis in rumiants:large-Scale epidemilogical survey, isolation of a new Eimeria zuernii strain and novel data on Eimeria spp. Host cel interactions

Abstract

ABSTRACT: Eimeria and has high economic impact on livestock worldwide. Oocysts of Eimeria spp. are found ubiquitously in the environment, making the infection almost inevitable. The massive replication of the parasite leads to the destruction of intestinal cells thereby producing diarrhoea and sometimes causing death. Furthermore, because of massive intestinal damage through obligate intracellular replication of Eimeria spp., the digestion and absorption of nutrients become affected and even without clinical symptoms animal performance is compromised, causing economical losses in cattle and goat industry. Although understanding of coccidiosis (mainly in chicken) has improved during the past decades, there is still a lack of information specifically in the field ruminant coccidiosis. Advanced tools for research on epidemiology, immunology, biology or diagnosis are now available opening new perspectives for modern research in this field. As part of this thesis, a large-scale cross-sectional epidemiological study was conducted to evaluate prevalence, species diversity and associated risk factors of Eimeria spp. infections in 55 cattle farms across seven states of Colombia. In total, 1333 fecal samples from young animals (<one year of age) were were examined. The overall Eimeria prevalence was 75.5%, with no difference observed between age categories. In total, 13 different Eimeria species were here identified. The most prevalent species was E. bovis (33.5%). Analysis of extrinsic associated risk factors revealed floor type, feeding system, watering system and herd size as significant (p < 0.05) risk factors for Eimeria infections. On the other hand, a Colombian E. zuernii strain was isolated and a corresponding suitable in vitro culture was established. The new E. zuernii (strain A) will allow detailed in vitro investigations on metabolism and on host innate/adaptive immunity for this specific bovine species. Additionally, we used novel tools in microscopy (e. g. 3D- holotomography analysis) to study exogenous sporogony of E. bovis and farther improved improved the excystation method to facilitate the work with ruminant Eimeria strains. Overall, three different E. bovis sporogony phases were documented: i) sporoblast/sporont transformation into sporogonial stages, ii) cytokinesis followed by nuclear division, and iii) formation of fully developed four sporocysts each with two developed sporozoites. Moreover, we generated first evidence on carbohydrate-related metabolic pathways and energy supply to be involved in E. bovis sporozoites-induced NETosis and simultaneous formation of autophagosomes. E. bovis-induced cell-free and anchored NETs. Both phenotypes were significantly diminished via inhibitor pretreatments of some metabolic of exposed PMN, thereby indicating a key role of ATP, pyruvate- and lactate-mediated metabolic pathways for proper sporozoite-mediated NETosis. Interestingly, E. bovis additionally induced LC3B-related autophagosome formation in parallel to NET formation in bovine PMN. Finally, we explored the metabolism of lipids during in vitro of caprine E. arloingi first merogony resulting in macromeront formation within host endothelial cells. The complete inhibition of merozoite I production in E. arloingi-treated host endothelial cells suggested that the uptake of lipids via SR-B1 is necessary for parasite replication within host cell. Although all this novel data leads to a better understanding of parasite-host/host cell interactions, we still need more investigation thoroughly on parasite-induced modulation of different cellular functions (e. g. apoptosis, autophagy, cytoskeleton, cholesterol metabolism) which may be altered during endogenous infection and taking particular care of adequate highly specific host cells. Thus, ruminant Eimeria spp.-related investigations in vitro should be conducted mainly in primary host cells corresponding to the ones parasitized in vivo. As such, ruminant pathogenic Eimeria species, all of them resulting in macromeront formation, replicate in vivo in lymphatic endothelial cells of the small intestinal villi. Key