TRANSMISSION OF OSELTAMIVIR-RESISTANT INFLUENZA A H1N1 VIRUSES IN GUINEA PIGS

描述（由申请人提供）：自从奥司他韦（Tamiflu(r)）上市以来，偶有从人身上分离出具有奥司他韦耐药性的甲型H1N1流感和甲型H3N2流感病毒，通常是从接受该药治疗的人身上分离出来的[41,43,66 -69]。先前的体外和体内数据表明，由于突变的神经氨酸酶（NA）的酶活性降低，耐药病毒比敏感病毒更不适合[18,48 - 50,70,71]。然而，季节性A/H1N1病毒中奥司他韦耐药流行率突然呈指数增长——2007年耐药不到1%，2008年耐药11%，2009年接近100%[51,52]——不能仅仅用选择性使用奥司他韦的压力来解释。这些对奥司他韦具有耐药性的A/H1N1病毒除了具有耐药性外，可能已进化出比敏感毒株更适合的优势；具体来说，耐药病毒可能在哺乳动物宿主之间更有效地传播。我们实验室的初步数据支持这一假设。对于季节性的A/H1N1病毒，旧的模式——在获得奥司他韦耐药性时，病毒变得不那么适合——可能不再成立。季节性A/H1N1病毒的不同传播性为探索耐药流感病毒如何进化以克服受损的哺乳动物传播性提供了及时和相关的案例研究。

DESCRIPTION (provided by applicant): Since the introduction of oseltamivir (Tamiflu(r)) to the market, oseltamivir-resistant influenza A/H1N1 and A/H3N2 viruses have occasionally been isolated from humans, usually from persons treated with the drug [41, 43, 66-69]. Previous in vitro and in vivo data suggested that drug-resistant viruses were less fit than sensitive strains, due to compromised enzymatic activity of the mutated neuraminidase (NA) [18, 48-50, 70, 71]. However, the sudden, exponential increase in the prevalence of oseltamivir resistance among seasonal A/H1N1 viruses - less than 1% resistant in 2007, 11% resistant in 2008, and near 100% resistant in 2009 [51, 52] - cannot be explained solely by selective pressure of oseltamivir use. These oseltamivir-resistant A/H1N1 viruses may have evolved a fitness advantage over sensitive strains, apart from drug resistance; specifically, resistant viruses may transmit more efficiently among mammalian hosts. Preliminary data from our laboratory supports this hypothesis. For seasonal A/H1N1 virus-es, the old paradigm - that, in acquiring oseltamivir resistance, viruses become less fit - may no longer hold true. The differential transmissibility of seasonal A/H1N1 viruses provides a timely and relevant case study to explore how drug-resistant influenza viruses evolve to overcome impaired mammalian transmissibility. The use of oseltamivir has dramatically increased during the current swine-origin A/H1N1 pandemic [72]; this has in turn increased the chances of selecting resistant viruses in novel A/H1N1-infected, oseltamivir-treated individuals. Indeed, in the seven months since the swine-origin A/H1N1 strain was first recovered from humans, more than 25 oseltamivir-resistant isolates have been detected worldwide, mainly (but not entirely) from oseltamivir-prophylaxed or -treated persons [54-56]. To date, all of these isolates have carried the same oseltamivir resistance mutation - a histidine-to-tyrosine change at residue 275 of the viral NA (NA-H275Y) - that is found in >99% of seasonal A/H1N1 viruses. Furthermore, seasonal A/H1N1 and A/H3N2 viruses have continued to co-circulate at low levels with swine-origin A/H1N1 viruses worldwide [56]; genetic reassortment among these strains could theoretically yield a novel human virus, with an oseltamivir-resistant N1 NA in combination with other seasonal and swine-origin genes. Using insights gleaned from our study of the differential transmissibility of oseltamivir-sensitive and -resistant seasonal A/H1N1 viruses, we propose to explore whether current oseltamivir-resistant swine-origin A/H1N1 isolates are less transmissible than sensitive strains, and, if so, how these viruses might evolve (like seasonal A/H1N1 viruses) to overcome any fitness deficiency that oseltamivir-resistance might confer. In 1973, E.D. Kilbourne wrote that the "student of influenza is constantly looking back over his shoulder and asking 'what happened?' in the hope that understanding of past events will alert him to the catastrophes of the future" [73]; in 2009, we find ourselves amidst the first influenza pandemic in forty years. It is our intention that, in understanding the recent evolution of oseltamivir-resistant seasonal A/H1N1 viruses, these experiments will not only be immediately applicable to the current A/H1N1 swine-origin influenza pandemic, but also might yield data that could inform our approach to antiviral prophylaxis and treatment in future pandemics. Project Narrative: In 2007, less than 1% of seasonal influenza A/H1N1 viruses were resistant to the oral anti-influenza drug oseltamivir (Tamiflu(r)); by 2009, nearly 100% had acquired a genetic mutation that rendered them drug resistant. We hypothesize that these viruses evolved in such a way that they became more transmissible among humans, and that it was more efficient transmission that allowed them to become so prevalent so quickly. The research we propose seeks to understand the genetic changes that occurred in seasonal A/H1N1 viruses to improve mammalian transmission, and in so doing, to assess the likelihood that oseltamivir-resistant swine-origin A/H1N1 viruses might evolve along a similar path to prevalence.