Abstract
Many of the emerging and re-emerging viral diseases that have caused global outbreaks in
recent years —such as severe acute respiratory syndrome (SARS), dengue fever, Zika virus disease,
and COVID-19 —are caused by positive-sense single-stranded RNA (+ssRNA) viruses. This review
focuses on members of the Flaviviridae family, a diverse group of +ssRNA viruses that exhibit
distinct host and tissue tropisms, and summarizes our recent efforts to elucidate the molecular
determinants underlying their pathogenicity and tropism. By refining reverse genetics systems that
enable precise manipulation of viral genomes, we have uncovered the functional roles of specific
viral proteins in pathogenesis through experimental infections using animal models that recapitulate
disease phenotypes. In addition, by analyzing structural variations within viral genomes, we
successfully identified key elements responsible for determining viral specificity. We have also
developed innovative viral reporter assays that incorporate advanced imaging technologies,
enabling real-time visualization of viral dynamics in vivo and facilitating diagnostic applications.
This review integrates these findings to provide insights into how pathogenicity and tissue tropism
evolve through repeated interspecies transmission, and discusses the potential of such approaches
as a foundational platform for future infectious disease research and countermeasures.
