Potency of nucleoside analogs against Powassan virus replication and identification of 4'-fluorouridine as a therapeutic candidate for tick-borne orthoflavivirus encephalitis

Authors

Lewis, D. S. M., Moore, T., Patel, R., Cox, R.

Abstract

Powassan virus (POWV) is an emerging tick-borne orthoflavivirus that causes severe encephalitis, long-term neurologic sequelae, and death, yet no approved antiviral therapies exist. Here, we evaluated several previously characterized nucleoside analogs as candidate countermeasures for POWV encephalitis. Favipiravir, molnupiravir, 4'-fluorouridine (4'-FlU), and GS-441524 inhibited POWV replication in vitro and demonstrated comparable activity against West Nile virus (WNV). We established C3H/HeNCrl mice as a stringent POWV disease model, showing increased susceptibility, higher day 7 brain titers, and more pronounced neurologic signs resembling severe human disease, compared with C57BL/6 mice. In prophylactic and therapeutic studies, 4'-fluorouridine was the most efficacious compound tested, significantly reducing brain viral burden even when treatment was delayed. Direct comparison with molnupiravir, favipiravir, and GS-441524 in mice confirmed superior survival benefit and antiviral activity for 4'-FlU against both POWV and WNV. These data identify 4'-fluorouridine as a promising therapeutic candidate for neurotropic flavivirus disease.

Preprint server: bioRxiv
The authors list and abstract were imported from bioRxiv on 27 Sep 2026.

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