Phylogenetic and genomic characterization of whole genome sequences of a herpes simplex virus type 1 isolate identified possible virulence determinants in a human subject with fulminant hepatitis

Herpes simplex virus 1 (HSV-1) is a rare cause of acute hepatitis, especially in patients with chronic immunosuppression. We performed whole-genome HSV-1 sequencing with a metagenomics approach on peripheral blood samples from an Italian case of fatal acute liver failure with high circulating HSV-1 (1,129,900,000 copies/mL), followed by phylogenetic analysis. After multiple sequence alignment, a final dataset of 182 whole-genome sequences was selected. The sequenced HSV-1 strain belonged to a phylogenetic clade isolated in Florida in 2002 (OQ724868.1). A characterization of single nucleotide polymorphisms and indels was performed to determine their effects on the viral genome: only one variant, classified as an indel, was detected with a high impact effect (c.905_906insGTTTT) in the UL49A gene, which is known to encode a membrane protein regulating virion morphogenesis, replication and assembly. In addition, this study also detected variants in other genes involved in crucial steps of the HSV-1 life cycle, like alpha-regulation (US7), capsid transport (UL36) and viral polymerase function (UL30). In conclusion, the results of this variant analysis confirmed that in HSV-1 hepatitis, some viral regions may be hotspots for adaptive mutations with a substantial impact on viral replication or immune evasion.