Effectiveness of nucleoside analogs against Wetland virus infection.

Wetland virus (WELV), a newly identified Orthonairovirus phylogenetically related to the Crimean-Congo hemorrhagic fever virus (CCHFV), has recently been shown to cause human infections. A portion of patients infected with WELV usually present with febrile diseases, accompanied by hemorrhagic and neurological symptoms. Currently, there are no reports demonstrating effective therapeutic drugs for the treatment of WELV. In this study, we evaluated the anti-WELV efficacy of five nucleoside analogs: four clinically approved drugs-ribavirin, remdesivir, molnupiravir, and sofosbuvir; and a clinical candidate 4'-fluorouridine. Ribavirin and 4'-fluorouridine strongly inhibited WELV replication in vitro. Remdesivir and molnupiravir showed limited antiviral activity against WELV in Huh7 cells but not in Vero cells, while sofosbuvir did not exhibit inhibitory effects. Utilizing a lethal immunocompetent mouse model of WELV infection, we found that oral administration of relatively low doses of ribavirin (25 mg/kg/day) or 4'-fluorouridine (2.5 mg/kg/day) significantly reduced the mortality of WELV-infected mice by decreasing viral titers in tissues and alleviating pathological damage. This treatment strategy retained significant efficacy even when initiated 2-4 days after infection. Additionally, we identified mutations G3033R and A3756V in the C-terminal region of the WELV L protein, which may be associated with viral resistance to ribavirin and 4'-fluorouridine. This study revealed varying degrees of anti-WELV efficacy among different nucleoside analogs and identified 4'-fluorouridine as a promising therapeutic candidate and ribavirin as a priority treatment option for WELV infection.