Viral evolution sustains a dengue outbreak of enhanced severity.

Compared to the previous 2013-2014 dengue outbreak, the 2016-2017 outbreak in New Caledonia was characterized by an increased number of severe forms associated with hepatic presentations. Some clinical and biological parameters along with a history of previous dengue infection were identified as risk factors predicting the development of severe dengue in patients in 2017 in New Caledonia. In this study, we assessed the virological factors associated with this enhanced severity. The genetic features of dengue virus (DENV)-1 strains collected in 2013-2014 and from severe and non-severe patients in 2016-2017 were characterized using whole-genome sequencing. Fitness, hepatic tropism and cytopathogenicity of DENV 2016-2017 strains were compared to those of DENV 2013-2014 strains using replication kinetics in the human hepatic cell line HuH7. Whole-genome sequencing identified four amino acid substitution specific to strains from 2016-2017 and absent from strains from 2013-2014. Three of these mutations occurred in predicted T cell epitopes, among which one was also a B cell epitope. Strains isolated from severe forms did not exhibit specific genetic features. DENV strains retrieved in 2016-2017 exhibited a trend towards reduced replicative fitness and cytopathogenicity in human hepatic cells compared to strains from 2013-2014. Overall, the 2016-2017 dengue outbreak in New Caledonia was associated with a viral genetic evolution which had limited impact on DENV hepatic tropism and cytopathogenicity. These mutations, however, may have modified the antigenicity of DENV strains from 2016-2017, altering the host immune response to DENV infection in some patients, in turn favoring the development of severe forms.Trial registration: ClinicalTrials.gov identifier: NCT04615364..