• Brian B Gowen, Terry L Juelich, Eric J Sefing, Trevor Brasel, Jennifer K Smith, Lihong Zhang, Bersabeh Tigabu, Terence E Hill, Tatyana Yun, Colette Pietzsch, Yousuke Furuta, and Alexander N Freiberg.
• Department of Animal, Dairy, and Veterinary Sciences, Utah State University, Logan, Utah, United States of America ; Institute for Antiviral Research, Utah State University, Logan, Utah, United States of America ; School of Veterinary Medicine, Utah State University, Logan, Utah, United States of America.
• PLoS Negl Trop Dis. 2013 Jan 1;7(12):e2614.

BackgroundJunín virus (JUNV), the etiologic agent of Argentine hemorrhagic fever (AHF), is classified by the NIAID and CDC as a Category A priority pathogen. Presently, antiviral therapy for AHF is limited to immune plasma, which is readily available only in the endemic regions of Argentina. T-705 (favipiravir) is a broadly active small molecule RNA-dependent RNA polymerase inhibitor presently in clinical evaluation for the treatment of influenza. We have previously reported on the in vitro activity of favipiravir against several strains of JUNV and other pathogenic New World arenaviruses.Methodology/Principal FindingsTo evaluate the efficacy of favipiravir in vivo, guinea pigs were challenged with the pathogenic Romero strain of JUNV, and then treated twice daily for two weeks with oral or intraperitoneal (i.p.) favipiravir (300 mg/kg/day) starting 1-2 days post-infection. Although only 20% of animals treated orally with favipiravir survived the lethal challenge dose, those that succumbed survived considerably longer than guinea pigs treated with placebo. Consistent with pharmacokinetic analysis that showed greater plasma levels of favipiravir in animals dosed by i.p. injection, i.p. treatment resulted in a substantially higher level of protection (78% survival). Survival in guinea pigs treated with ribavirin was in the range of 33-40%. Favipiravir treatment resulted in undetectable levels of serum and tissue viral titers and prevented the prominent thrombocytopenia and leucopenia observed in placebo-treated animals during the acute phase of infection.Conclusions/SignificanceThe remarkable protection afforded by i.p. favipiravir intervention beginning 2 days after challenge is the highest ever reported for a small molecule antiviral in the difficult to treat guinea pig JUNV challenge model. These findings support the continued development of favipiravir as a promising antiviral against JUNV and other related arenaviruses.

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