Effective oral favipiravir (T-705) therapy initiated after the onset of clinical disease in a model of arenavirus hemorrhagic Fever

Abstract

Background: Lassa and Junín viruses are the most prominent members of the Arenaviridae family of viruses that cause viral hemorrhagic fever syndromes Lassa fever and Argentine hemorrhagic fever, respectively. At present, ribavirin is the only antiviral drug indicated for use in treatment of these diseases, but because of its limited efficacy in advanced cases of disease and its toxicity, safer and more effective antivirals are needed.

Methodology/principal findings: Here, we used a model of acute arenaviral infection in outbred guinea pigs based on challenge with an adapted strain of Pichindé virus (PICV) to further preclinical development of T-705 (Favipiravir), a promising broad-spectrum inhibitor of RNA virus infections. The guinea pig-adapted passage 19 PICV was uniformly lethal with an LD(50) of ∼5 plaque-forming units and disease was associated with fever, weight loss, thrombocytopenia, coagulation defects, increases in serum aspartate aminotransferase (AST) concentrations, and pantropic viral infection. Favipiravir (300 mg/kg/day, twice daily orally for 14 days) was highly effective, as all animals recovered fully from PICV-induced disease even when therapy was initiated one week after virus challenge when animals were already significantly ill with marked fevers and thrombocytopenia. Antiviral activity and reduced disease severity was evidenced by dramatic reductions in peak serum virus titers and AST concentrations in favipiravir-treated animals. Moreover, a sharp decrease in body temperature was observed shortly after the start of treatment. Oral ribavirin was also evaluated, and although effective, the slower rate of recovery may be a sign of the drug's known toxicity.

Conclusions/significance: Our findings support further development of favipiravir for the treatment of severe arenaviral infections. The optimization of the experimental favipiravir treatment regimen in the PICV guinea pig model will inform critical future studies in the same species based on challenge with highly pathogenic arenaviruses such as Lassa and Junín.

Conflict of interest statement

YF is employed by the Toyama Chemical Co., Ltd., the manufacturer of favipiravir.

Figures

Figure 1. Titration of PICV in outbred guinea pigs.

Hartley guinea pigs were challenged i.p. with 50,000, 5000, 500, 50, 5, 0.5 (n = 4/group), or 0.05 PFU (n = 3) p19 PICV and survival plotted over a 28-day post-infection (p.i.) period. The data are combined from two separate experiments.

Figure 2. Natural history of disease caused by PICV infection in guinea pigs.

Animals were challenged with 500 PFU of p19 PICV, (A) daily weights and temperatures were recorded, and groups of 3 were sacrificed on the indicated day p.i. for collection of blood and tissues for analysis of (B) PT and aPTT clot times, (C) PLT counts, (D) serum AST levels, (E) infectious serum and tissue virus titers, and (F) splenomegaly during the course of infection. Due to a technical problem, PT clot times were not detected in two of three animals on day 1. *P<0.05 compared to day 1 p.i. (day 3 p.i. for PT).

Figure 3. Treatment of lethal PICV infection with favipiravir starting 4 days after challenge.

Guinea pigs (n = 8/group) challenged with 500 PFU of p19 PICV were treated twice daily for 14 days with favipiravir, ribavirin, or placebo beginning on day 4 of infection (capped hashed line). Animals receiving favipiravir were initially fed 100 and 30 mg/kg/d (days 4 to 7) before increasing the doses to 300 and 90 mg/kg/d, respectively, starting on day 8 (indicated by arrow). (A) Survival, (B) body weights, and (C) temperatures were monitored for 29 days. Serum was collected on day 11 for analysis of (D) AST and (E) viremia, with the exception of two moribund animals from the placebo group that had to be sacrificed on day 10. *P<0.05 compared to placebo-treated animals.

Figure 4. Favipiravir treatment of advanced PICV infection in guinea pigs.

Guinea pigs (n = 7–8/group) challenged with 500 PFU of p19 PICV were treated with the indicated dosages of favipiravir, ribavirin, or placebo beginning on day 7 of infection. The 150-mg/kg/d group received a loading dose of 300 mg/kg/d on the first day of treatment. Drugs were administered twice daily for 14 days (capped hashed line) and (A) survival, (B) body weights, and (C) temperatures were monitored for 36 days. Serum was collected on day 10 for analysis of (D) AST and (E) viremia. *P<0.05 compared to placebo-treated animals.