ABSTRACT As underscored by pandemic COVID-19, Zika, yellow fever and chikungunya viruses, new and emerging viruses represent increasing threats to human health, yet their mechanisms of emergence remain poorly understood, and effective interventions are not available for most. Research on their pathogenesis, ecology, evolution, epidemiology, emergence mechanisms, diagnostics, vaccines and therapeutics remain critical public health needs. The World Reference Center for Emerging Viruses and Arboviruses (WRCEVA) comprises a comprehensive, diverse collection of over 8,000 virus strains in 21 families, as well as antisera, antigens, cDNA clones and other reagents to enable research worldwide. Approximately 400 new virus strains are added annually, and 1000 viruses and reagents are shipped annually. The WRCEVA also maintains broad expertise in both novel and traditional approaches to virus identification and characterization, and provides critical support for emergency outbreak responses as exemplified by the rapid generation and distribution of critical COVID and Zika reagents. This proposal seeks to continue these WRCEVA activities in support of NIH-funded and other research on emerging viruses worldwide, through five Specific Aims: 1. Maintain a comprehensive set of emerging viruses, arboviruses and associated reagents to support research and surveillance. The virus collection as well as antigens, antibodies, cDNA clones and other reagents will be continually enhanced to capitalize on new emergence trends and technologies. Emphasis during the first two years will be placed on the development of critical reagents for coronavirus research. 2. Discover, isolate and characterize newly acquired viruses to determine relationships and taxonomic assignments, and to assess in vitro and in vivo host range. Clinical and field samples as well as viral isolates will be received for identification and characterization, and added to the repository. Critical phenotypes of newly discovered viruses and strains will be assessed by using in vitro and in vivo infections. 3. Perform sequencing and phylogenetic analyses of selected virus groups to determine evolutionary histories and emergence mechanisms, patterns of spread/infection, and to rapidly determine the sources of new outbreaks. Key virus strains will undergo genomic sequencing to generate databases that can be exploited for the rapid determination of new outbreak sources, including potential bioterrorism. 4. Determine why yellow fever virus has not caused major urban epidemics in South America for many decades, or ever in Asia. Our unique collection of virus strains and arbovirology expertise will be used to examine hypotheses related to limitations on urban transmission by Aedes aegypti mosquitoes. 5. Train scientists in the identification and characterization of emerging viruses. To enhance research and surveillance in the U.S. and worldwide, the most efficient way to limit spread of new outbreaks,...