No abstract

A number of New World arenaviruses (Junín [JUNV], Machupo [MACV], and Guanarito [GTOV] viruses)can cause human disease ranging from mild febrile illness to a severe and often fatal hemorrhagic fever syndrome. These highly pathogenic viruses and the Old World Lassa fever virus pose a significant threat to public health and national security. The only licensed antiviral agent with activity against these viruses, ribavirin, has had mixed success in treating severe arenaviral disease and is associated with significant toxicities. A novel pyrazine derivative currently in clinical trials for the treatment of influenza virus infections, T-705 (favipiravir), has demonstrated broad-spectrum activity against a number of RNA viruses, including arenaviruses. T-705 has also been shown to be effective against Pichinde arenavirus infection in a hamster model. Here, we demonstrate the robust antiviral activity of T-705 against authentic highly pathogenic arenaviruses in cell culture. We show that T-705 disrupts an early or intermediate stage in viral replication, distinct from absorption or release, and that its antiviral activity in cell culture is reversed by the addition of purine bases and nucleosides, but not with pyrimidines. Specific inhibition of viral replication/transcription by T-705 was demonstrated using a lymphocytic choriomeningitis arenavirus replicon system. Our findings indicate that T-705 acts to inhibit arenavirus replication/transcription and may directly target the viral RNA-dependent RNA polymerase.

BackgroundLassa 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 FindingsHere, 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 LD50 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/SignificanceOur 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.

Many insects use a fairly well‐defined set of host plants, but are occasionally observed on an atypical host. The seed beetle Callosobruchus maculatus (F.) (Coleoptera: Chrysomelidae: Bruchinae) has rarely been reported to attack lentil, which is distantly related to its usual legume hosts. An initial assay of an Asian beetle population revealed that none of the 100 larvae entering lentil seeds survived to adult emergence. Nevertheless, three attempts at mass selection, in which more than 2 000 adults were added to lentil seeds, eventually yielded self‐sustaining populations. In each case, a severe bottleneck was followed by a rapid increase in survival, which exceeded 65% after only five generations and surpassed 85% in <20 generations. Subsequent large‐scale experiments indicated that survival in lentil is initially <2% and that most larvae die before they have completely entered a seed. The only potential trade‐off associated with rapid adaptation to lentil was a modest increase in the time required to develop in the ancestral host, mung bean. Reciprocal crosses between a lentil‐adapted line (F10) and a mung‐bean line produced offspring with intermediate survival, very long development times, and small size. Although the Asian population has been kept under uniform laboratory conditions for more than 200 generations, it appears to maintain rare alleles that permit the colonization of an extremely poor host. Such standing genetic variation can account for the sporadic appearance of unusual ‘biotypes’ among herbivorous insects.

Successful host shifts by herbivorous insects may require the modification of multiple larval and adult traits. The seed beetle Callosobruchus maculatus (F.) (Coleoptera: Bruchidae) rarely attacks lentil (Lens culinaris Medikus), which is distantly related to its typical hosts. In a previous study, larval survival in lentil seeds increased from &lt;2 to &gt;85% in fewer than 20 generations of laboratory selection. However, lentil is also a poor oviposition host; lifetime fecundity on lentil was initially less than a third of that on the ancestral host [ mung bean, Vigna radiata (L.) R. Wilczek ] and one fourth of females did not even recognize lentil as a potential host. This study examined the genetic lability of host acceptance. We performed both quasi-natural selection, in which replicate lines switched to lentil were compared with those remaining on mung bean, and artificial selection, in which lines were established using females from the base population that exhibited especially low or high acceptance of lentil during a short-term assay. After only five to eight generations of quasi-natural selection, lifetime fecundity on lentil was 2 to 3 times higher in the lentil lines than in the mung bean lines. Lentil-line females also accepted the novel host sooner after adult emergence. Similarly, a single generation of artificial selection was sufficient to increase oviposition on lentil in the acceptance line. Host acceptance was not genetically correlated with larval survival, which remained &lt;2% in lines artificially selected for either high or low acceptance of lentil seeds. Although modification of oviposition behavior in this study was not nearly as striking as the increase in larval survival reported previously, the C. maculatus population possessed enough standing genetic variation in both larval physiology and adult behavior to permit rapid adaptation to a very poor host.