Yellow fever virus (YFV), a member of the Flaviviridae family, is an arthropod-borne virus that can cause severe disease in humans with a lethality rate of up to 60%. Since 2017, increases in YFV activity in areas of South America and Africa have been described. Although a vaccine is available, named strain 17D (Theiler and Smith, 1937), it is contraindicated for use in the elderly, expectant mothers, immunocompromised people, among others. To this day there is no antiviral treatment against YFV to reduce the severity of viral infection. Here, we used a circular polymerase extension reaction (CPER)-based reverse genetics approach to generate a full-length reporter virus (YFVhb) by introducing a small HiBit tag in the NS1 protein. The reporter virus replicates at a similar rate to the parental YFV in HuH-7 cells. Using YFVhb, we designed a high throughput antiviral screening luciferase-based assay to identify inhibitors that target any step of the viral replication cycle. We validated our assay by using a range of inhibitors including drugs, immune sera and neutralizing single chain variable fragments (scFv). In light of the recent upsurge in YFV and a potential spread of the virus, this assay is a further tool in the development of antiviral therapy against YFV.

Background: Multiple severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants emerged globally during the recent coronavirus disease (COVID-19) pandemic. From April 2020 to April 2021, Thailand experienced three COVID-19 waves, and each wave was driven by different variants. Therefore, we aimed to analyze the genetic diversity of circulating SARS-CoV-2 using whole-genome sequencing analysis. Methods: A total of 33 SARS-CoV-2 positive samples from three consecutive COVID-19 waves were collected and sequenced by whole-genome sequencing, of which, 8, 10, and 15 samples were derived from the first, second, and third waves, respectively. The genetic diversity of variants in each wave and the correlation between mutations and disease severity were explored. Results: During the first wave, A.6, B, B.1, and B.1.375 were found to be predominant. The occurrence of mutations in these lineages was associated with low asymptomatic and mild symptoms, providing no transmission advantage and resulting in extinction after a few months of circulation. B.1.36.16, the predominant lineage of the second wave, caused more symptomatic COVID-19 cases and contained a small number of key mutations. This variant was replaced by the VOC alpha variant, which later became dominant in the third wave. We found that B.1.1.7 lineage-specific mutations were crucial for increasing transmissibility and infectivity, but not likely associated with disease severity. There were six additional mutations found only in severe COVID-19 patients, which might have altered the virus phenotype with an inclination toward more highly pathogenic SARS-CoV-2. Conclusion: The findings of this study highlighted the importance of whole-genome analysis in tracking newly emerging variants, exploring the genetic determinants essential for transmissibility, infectivity, and pathogenicity, and helping better understand the evolutionary process in the adaptation of viruses in humans.

Louping ill virus (LIV) is a tick-borne flavivirus that predominantly causes disease in livestock, especially sheep in the British Isles. A preventive vaccine, previously approved for veterinary use but now discontinued, was based on an inactivated whole virion that likely provided protection by induction of neutralizing antibodies recognizing the viral envelope (E) protein. A major disadvantage of the inactivated vaccine was the need for high containment facilities for the propagation of infectious virus, as mandated by the hazard group 3 status of the virus. This study aimed to develop high-efficacy non-infectious protein-based vaccine candidates. Specifically, soluble envelope protein (sE), and virus-like particles (VLPs), comprised of the precursor of membrane and envelope proteins, were generated, characterized, and studied for their immunogenicity in mice. Results showed that the VLPs induced more potent virus neutralizing response compared to sE, even though the total anti-envelope IgG content induced by the two antigens was similar. Depletion of anti-monomeric E protein antibodies from mouse immune sera suggested that the neutralizing antibodies elicited by the VLPs targeted epitopes spanning the highly organized structure of multimer of the E protein, whereas the antibody response induced by sE focused on E monomers. Thus, our results indicate that VLPs represent a promising LIV vaccine candidate.

Peer reviewed article authored by (Noda M, Masrinoul P, Punkum C, Pipattanaboon C, Ramasoota P, Setthapramote C, Sasaki T, Sasayama M, Yamashita A, Kurosu T, Ikuta K, Okabayashi T). Read article or submit your manuscript for publishing.