Molecular and phylogenetic characterization of the highly pathogenic avian influenza H5N1 virus detected in the Republic of Moldova

Introduction The H5N1 avian influenza virus is one of the most virulent antigenic combinations, including those with zoonotic pathogenic potential. As the number of avian influenza outbreaks has increased globally, a corresponding rise in outbreaks caused by this virus has also been recorded in the Republic of Moldova. Materials and methods The descriptive study employed epidemiological, clinical and molecular biology (RT-PCR) research methods. The research material consisted of carcasses of domestic and wild birds, as well as blood serum samples collected from various regions of the republic. Identification of the influenza virus in the research material was carried out at the National Reference Laboratory Public Institution National Center for Animal, Plant Health and Food Safety (P.I. NCAPHFS) and the EU Reference Laboratory (EURL, IZSVe). The following diagnostic kits were used for virus identification: the "IndiSpin® Pathogen Kit" (QIAGEN® GmbH for INDICAL BIOSCIENCE) and the "Virotype® Influenza A RT-PCR Kit" (Germany). Results The molecular structure of HPAI A(H5N1) viruses isolated from the Republic of Moldova demonstrated the presence of genetic mutations in the PB2 protein (E627K and/or D701N) associated with viral adaptation to mammalian hosts and isolates with European H5 viruses belonging to the EA-2021-I, EA-2022-CH, EA-2022-AB, and EA-2023-DB genotypes. Conclusions The molecular characterization of HPAI A(H5N1) isolated from birds in the Republic of Moldova demonstrated the presence of genetic mutations in the PB2 protein and in the hemagglutinin protein (S133A, S154N, and T156A), which are associated with adaptation to human-type receptors.