Resurgence of zoonotic highly pathogenic avian influenza H5N1 virus in Cambodia

Overview Recent surveillance data from Cambodia reveal a concerning resurgence of zoonotic human infections with highly pathogenic avian influenza (HPAI) H5N1 after more than a decade of apparent absence. Between February 2023 and August 2024, sixteen laboratory-confirmed human cases were identified—most occurring in children and adolescents with direct exposure to infected poultry. These cases were detected across multiple provinces, primarily as isolated household infections, though limited household clusters were reported. Mortality reached approximately 38%, aligning with historical H5N1 case fatality rates observed in Southeast Asia. Enhanced laboratory diagnostic capacity—strengthened during the COVID-19 pandemic—was instrumental in detecting these infections, utilizing national influenza-like illness (ILI) and severe acute respiratory infection (SARI) surveillance systems. Genomic and epidemiological findings Genomic sequencing of isolates from both human cases and surrounding poultry confirmed avian origins for all transmissions. Outbreaks corresponded to at least two distinct viral genotypes: the regionally persistent H5N1 clade 2.3.2.1e (formerly classified as 2.3.2.1c) and a novel...