The project mainly focuses on two areas: (i) the understanding of host-virus relationships, and (ii) the detection of infectious agents (including new variants and previously unknown). These areas have both conceptual and methodological similarities and the long-term goal is to better understand why certain microorganisms are pathogenic while other, genetically similar, variants are harmless. For example: How does pathogenicity arise and how can we recognize potentially harmful microorganisms? How are microorganisms being transferred between hosts, and how is host-range and vector-transmission regulated on a genetic and molecular level? A related question is how microorganism quickly can evolve and gain new abilities, such as different types of resistances, upon changing conditions. Another challenge is to understand the individual contribution of specific microorganisms in complex and multifactorial disease scenarios (i.e. diseases caused by combinations of contributing factors rather than single pathogens). These are all highly relevant topics within both veterinary and human medicine in agreement with the 'one-health' concept.