Rotaviruses, especially the type rotavirus A (RVA), are the most significant causative agents of gastroenteritis in children and young animals. Numerous studies have confirmed the sporadic zoonotic transmission of RVA. Recent findings regarding saliva as a possible source of infection have changed the previous paradigm of exclusively fecal-oral transmission. The proposed retrospective and prospective study will answer many open questions, applying the principles of "One Health". Primarily, it will expand knowledge about the prevalence of zoonotic RVA strains in urban and rural areas of continental Croatia, possibly more prevalent in children with milder clinical symptoms, which are the focus of this research. Additionally, it will contribute significantly to understanding the significance of saliva and nasopharyngeal secretions as possible sources of RVA infection in humans and cattle. By employing advanced molecular methods and bioinformatics tools, the molecular epidemiology and genetic characteristics of complete RVA genomes in humans and cattle will be investigated, including the impact of genetic rearrangement and recombination on genetic diversity, as well as differences in the composition of oral microbiota relative to differences in RVA shedding in feces and saliva. The proposed interdisciplinary team of veterinarians, epidemiologists, clinical microbiologists, and medical physicists ensures an adequate and sustainable approach to addressing the project's challenges. The set objectives and planned outcomes ensure a valuable contribution to the institution's program goals and strengthen scientific competencies and international recognition of the research group.