Role of Influenza D Virus in Bovine Respiratory Disease: implications of coinfections and detection in Sweden

This thesis investigates the role of Influenza D virus (IDV) in bovine respiratory disease (BRD), with a focus on detection of IDV in Sweden and interactions with other respiratory pathogens. BRD is a multifactorial disease with a significant impact on cattle health and productivity. The presence of IDV in cattle is increasingly detected worldwide and is considered a potential co-pathogen in BRD. The work included seroepidemiological surveillance using bulk tank milk and ELISA, phylogenetic characterization of Swedish IDV isolates by RT-qPCR and whole genome sequencing, and experimental models used to study coinfections with Mycoplasmopsis (Mycoplasma) bovis, bovine respiratory syncytial virus and bovine parainfluenza virus 3. Proteomic and lipidomic analyses of bronchoalveolar lavage samples from co-infected calves revealed alterations in host immune responses and inflammatory pathways. In vitro studies further demonstrated that IDV changed the expression of key innate immune regulators, particularly during coinfections. These findings support a modulatory role for IDV in BRD pathogenesis and highlight its importance in surveillance.