Reduction of Neuraminidase Activity Exacerbates Disease in 2009 Pandemic Influenza Virus-Infected Mice

Abstract

During the first wave of the 2009 pandemic, caused by a H1N1 influenza virus (pH1N1) of swine origin, antivirals were the only form of therapeutic available to control the proliferation of disease until the conventional strain-matched vaccine was produced. Oseltamivir is an antiviral that inhibits the sialidase activity of the viral neuraminidase (NA) protein and was shown to be effective against pH1N1 viruses in ferrets. Furthermore, it was used in humans to treat infections during the pandemic and is still used for current infections without reported complication or exacerbation of illness. However, in an evaluation of the effectiveness of oseltamivir against pH1N1 infection, we unexpectedly observed an exacerbation of disease in virus-infected mice treated with oseltamivir, transforming an otherwise mild illness into one with high morbidity and mortality. In contrast, an identical treatment regime alleviated all signs of illness in mice infected with the pathogenic mouse-adapted virus A/WSN/33 (H1N1). The worsened clinical outcome with pH1N1 viruses occurred over a range of oseltamivir doses and treatment schedules and was directly linked to a reduction in NA enzymatic activity. Our results suggest that the suppression of NA activity with antivirals may exacerbate disease in a host-dependent manner by increasing replicative fitness in viruses that are not optimally adapted for replication in that host. IMPORTANCEHere, we report that treatment of pH1N1-infected mice with oseltamivir enhanced disease progression, transforming a mild illness into a lethal infection. This raises a potential pitfall of using the mouse model for evaluation of the therapeutic efficacy of neuraminidase inhibitors. We show that antiviral efficacy determined in a single animal species may not represent treatment in humans and that caution should be used when interpreting the outcome. Furthermore, increased virulence due to oseltamivir treatment was the effect of a shift in the hemagglutinin (HA) and neuraminidase (NA) activity balance. This is the first study that has demonstrated that altering the HA/NA activity balance by reduction in NA activity can result in an increase in virulence in any animal model from nonpathogenic to lethal and the first to demonstrate a situation in which treatment with a NA activity inhibitor has an effect opposite to the intended therapeutic effect of ameliorating the infection.

A Highly Pathogenic Avian H7N9 Influenza Virus Isolated from A Human Is Lethal in Some Ferrets Infected via Respiratory Droplets

“…However, we found that treatment with NA inhibitors had little-to-no effect on body weight loss and/or lung virus titers in mice infected with the NA inhibitor-sensitive virus (Figure 7). Similar findings were obtained with LPAI H7N9 and 2009 pandemic H1N1 viruses; mice infected with NA inhibitor-sensitive variants of these viruses and treated with NA inhibitors showed body weight loss (Ranadheera et al, 2016; Watanabe et al, 2013). Thus, the NA inhibitors may not provide effective treatment against the NA inhibitor-sensitive viruses of some influenza A virus subtypes in the mouse model.…”

Adaptive mutations of neuraminidase stalk truncation and deglycosylation confer enhanced pathogenicity of influenza A viruses

“… 43 , NA stalk truncation might reduce the structural flexibility of NA enzymatic pocket, and, as a result, it would restrain NA affinity for its substrate. Similar to a limited access theory of short stalk NAs 34 , 44 , 45 , the flexibility constraint of NA enzymatic pocket caused by NA stalk truncation 43 and the reduction of NA enzymatic activity due to antiviral treatment 46 also suggested the increase of viral pathogenicity. When the NA stalk mutations applied to the NA of H7N9 vaccine virus, based on the sequence alignment with the N1 subtype NA protein, the rH7N9/NA:Δ57–65 and rH7N9/NA:N63T viruses also exhibited enhanced viral pathogenicity in mice (Figs 8 and 9 ).…”

Biological Characterizations of H5Nx Avian Influenza Viruses Embodying Different Neuraminidases

“…The balance between HA and NA proteins contributes to expression of the HPAI phenotype ( Diederich et al, 2015 ). Furthermore, the NA gene has been shown to play an important role in influenza virus enzyme activity, transmission, and pathogenicity ( Lv et al, 2015 ; Stech et al, 2015 ; Ranadheera et al, 2016 ).…”