Experimental models of avian coccidiosis to investigate the antiparasitic activity of natural bioactive substances

Coccidiosis, a disease caused by Eimeria parasites, poses a significant threat to the poultry industry with resistance to conventional drugs emerging. Botanical alternatives like essential oils and nature-identical compounds offer a promising path toward sustainable and effective coccidiosis control, but often lack thorough evaluation. This thesis investigates the efficacy of botanical extracts as anticoccidials with in vitro and in vivo models, highlighting their effects on the host and the parasite. Invasion and development assays on cell cultures, like Madin-Darby Bovine Kidney (MDBK) cells and primary chicken intestinal epithelial cells (cIEC) characterized the efficacy of anticoccidial drugs and bo-tanical molecules, revealing that garlic, oregano and thyme oils, thymol, and carvacrol, exhibit notable an-ticoccidial effects by inhibiting invasion in cells, causing morphological aberrations in sporozoites, and de-creasing pro-inflammatory cytokines in cIEC. Also, E. tenella schizogony in MDBK cells was hindered by essential oils, with similar efficacy to conventional anticoccidials, suggesting synergistic actions within their diverse compositions. In an in vivo trial, a botanical-based feed additive was evaluated during acute E. tenella infection, with sal-inomycin as a comparison. Both treatments mitigated cecal lesions and oocyst output. Transcriptomic analysis revealed the modulation of immunity-related genes, cytokines, and other pathways. Salinomycin demonstrated broader impacts, influencing inflammation and oocyst wall formation, while the feed addi-tive mainly modulated inflammatory response and invasion-related genes. A second field trial investigated the feed additive's impact on broiler growth performance post-coccidiosis vaccination, showing improved body weight and feed conversion ratio, demonstrating its potential to alle-viate the negative effects of vaccination. Gene expression analysis indicated a positive influence on im-mune response, tight junctions, and nutrient transporters. In conclusion, these studies evidence the potential of plant-derived compounds and botanical feed addi-tives in combating coccidiosis. Their multifaceted actions offer promising paths for developing safer and characterized anticoccidial solutions in poultry production.