Antiviral Drugs Against Severe Fever With Thrombocytopenia Syndrome Virus Infection

Takayama-Ito, Mutsuyo; Saijo, Masayuki

The efficacy of favipiravir in vivo has been examined using animal models ( Table 2) . The intraperitoneal (i.p.) administration of favipiravir at a dose of 60 or 300 mg/kg/day for 5 days completely protected mice from death upon SFTSV infection, causing only a slight reduction in weight (Tani et al., 2016) . On the other hand, ∼40% of the mice treated with Frontiers in Microbiology | www.frontiersin.org ribavirin (i.p.) at a dose of 25 or 100 mg/kg/day lost body weight and died from SFTSV infection with reduction of the case fatality rate. All favipiravir-treated mice survived when the treatment was initiated on or earlier than 3 days post infection, whereas the mice treated at 4 and 5 days post infection exhibited 83% and 50% survival, respectively (Tani et al., 2016) . These results demonstrated that favipiravir would be potentially effective for prophylactic use and also for treating of SFTSV infections. Generally, favipiravir is orally administrated to humans. The oral administration (p.o.) of favipiravir showed similar efficacy to that of i.p. administration in a mouse model (Tani et al., 2016) . Furthermore, treatment with favipiravir (300 or 150 mg/kg/day) provided complete protection against a lethal SFTSV challenge in a STAT2 knockout golden Syrian hamster model . Additionally, the efficacy of favipiravir at practical dosages of 120 and 200 mg/kg/day p.o. was investigated in a mouse infection model, and all the mice survived when the treatment was initiated at no later than 4 days post infection (Tani et al., 2018) .