Antiviral Drugs Against Severe Fever With Thrombocytopenia Syndrome Virus Infection

Takayama-Ito, Mutsuyo; Saijo, Masayuki

Favipiravir (T-705), which was discovered and synthesized by Toyama Chemical Co., Ltd., exerts a broad spectrum of activity against various RNA viruses, including the influenza virus, arenaviruses, bunyaviruses, West Nile virus, yellow fever virus, and foot-and-mouth disease virus (Furuta et al., 2009) . Favipiravir is converted to its active form, ribofuranosyl-5triphosphate, by host enzymes and inhibits viral RNA polymerase in the host cells. Only a few reports have indicated resistance to favipiravir in vitro (Delang et al., 2014; Goldhill et al., 2018) . As shown in Tables 1, 2 favipiravir significantly inhibits SFTSV replication in vitro (Tani et al., 2016; Baba et al., 2017) and in vivo (Tani et al., 2016 (Tani et al., , 2018 Smee et al., 2018) . Furthermore, the IC 90 of favipiravir (22 µM) in Vero cells (Tani et al., 2016) was lower than that of ribavirin (263 µM) (Shimojima et al., 2014) .