新型欧亚类禽H1N1猪流感病毒致病与传播机制研究

Swine influenza viruses can infrequently infect humans. The first reported SIV human case was reported in 1958 in Czechoslovakia. The largest outbreak of Classical Swine H1N1 virus occurred in Fort Dix of United States in 1976. After 2009 H1N1 pandemic, human infections with H1N1v and H3N2v viruses with M gene derived from influenza A(H1N1)pdm09 have occurred continuously and increased significantly in recent years. Two human cases with Eurasian H1N1 (EA-H1N1) virus infections have been previously reported in China. A recent study based on the prevalence, genetics, and transmissibility characterizations of EA H1N1 SIVs showed that the virus preferentially binds to human-type receptors, and a portion of the tested viruses were transmitted to ferrets by respiratory droplets, raising the EA H1N1 viruses a great threat to humans. .In 2015, an influenza A (H1N1) virus (A/Hunan/42443/2015 [HuN, H1N1]) was isolated from a boy who had severe pneumonia in China. Genetically, the virus was a reassortant of Eurasian avian-like virus; Two surface genes and the M gene of the virus were highly similar with Eurasian avian-like (EA) swine H1N1 virus, while four internal genes (PB2, PB1, PA and NP) of the virus originated from the influenza A(H1N1)pdm09 virus. Based on our previous study, infection of the virus in a mouse model showed that the reassortant HuN H1N1 virus had higher infectivity and virulence than another EA H1N1 human isolate (A/Jiangsu/1/2011 [JS1, EA H1N1] virus). Based on the results of pathogenicity and genetic of HuN and JS1 viruses, the viral RNA dependent RNA polymerase (RdRp), which formed by the PB1, PB2, and PA subunits, could be the major determinant of transmission and pathogenesis of HuN virus. RNP activities were found to be related with viral replications and virulence. Our study would focus on the function of the novel reassorted EA H1N1 virus and the relation of the RNP functionality on its pathogenicity and transmissibility.

欧亚类禽猪流感病毒(EA H1N1) “是当前动物流感病毒中，引起下次人流感大流行可能性最大的病毒”。2011年和2012年我国先后报道了两例人感染欧亚类禽猪流感病毒(EA H1N1)病例，其中一例病例死亡。2015年，我国从一例重症病例身上分离到一株重配EA H1N1病毒(A/Hunan/42443/2015，HuN)。该病毒的两个表面基因和M基因来自EA H1N1病毒，而聚合酶复合物(RNP)基因PB2、PB1、PA和NP来自09pdm H1N1，这是第一次从人中分离到该病毒。我们前期的研究结果表明，与以往感染人的EA H1N1病毒相比，HuN病毒在小鼠中的感染力、复制力和毒力均显著增加。因此，我们后续的研究拟集中在新型重配EA H1N1病毒的RNP上，研究RNP对EA H1N1流感病毒致病力和传播力的影响，从而为EA H1N1猪流感病毒的防控提供科学的理论依据。

欧亚类禽猪流感病毒被认为是引起下次大流行可能性最大的动物流感病毒之一。在我国，感染人的欧亚类禽猪流感病毒可分为两大基因型：JS1-like和HuN-like基因型，其中JS1-like基因型病毒对小鼠不致病，而HuN-like基因型病毒能导致小鼠死亡。为了研究不同基因型病毒致病力表型不同的分子机制，本研究综合使用反向遗传学和体外体内实验，结果发现NP基因决定了欧亚类禽猪流感病毒在小鼠模型中的致病力，而NP上的三个氨基酸位点具有显著的种属特异性，分别为305，313和357位点。其中，NP-Q357K可显著增加欧亚类禽猪流感病毒的致病力。因此，本研究发现了新的影响欧亚类禽猪流感病毒致病力的分子标记，即NP-Q357K。其中357Q病毒在禽中流行，进入猪群后，357Q突变成357K，357K病毒进一步经筛选后突破种属屏障进入到人群，并在人群中流行。Q到K的氨基酸突变能显著增加欧亚类禽猪流感病毒在小鼠中的致病力，即导致小鼠由不死亡到死亡的表型变化。