Phylogenetic Analysis And Airborne Spread Characteristics Between Guinea Pigs Of Swine-origin Influenza A (H1N1) Virus

In April2009, swine-origin2009A (H1N1) influenza viruses (2009(H1N1)IV)were found in Mexico and the United States for the first time, and quickly spreadthroughout the world, presenting a significant threat to public health.2009(H1N1)IVis a novel triple-reassortant influenza virus derived from porcine, human, and avianinfluenza viruses, the polymerase basic-2(PB2) and polymerase A (PA) segments ofNorth American avian virus origin, the polymerase basic-1(PB1) gene of humanH3N2virus origin, the hemagglutinin (HA), nuclear protein (NP) and non-structual(NS) genes of classical swine origin and the neuraminidase (NA) and matrix (M)segments from Eurasian swine virus origin. Different from seasonal influenza viruses,humans lack immunity to this new virus, and thus the virus quickly caused apandemic.It has been determined that despite the complex causes of the novel H1N1epidemic, the airborne spread characteristic of S-O2009IV was one of the majorreasons for the widespread nature of this epidemic. Once formed, aerosols, includingthose containing viruses, can rapidly spread to a larger area with the assistance ofsignificant airflow. However, little is known about the development, transmission, andinfection via aerosols formed after infection with these subtypes of influenza viruses,and there is still some debate about airborne infection of these viruses.At the beginning of2011, an epidemic of the novel A/H1N1influenza occured inpig farms in Shandong province. Therefore, we used the Shandong isolate as theresearch object to carry out this study. Firstly, molecular characteristics of the eightfragments were all analyzed to determine the genetic traits. Then, based on guinea pigmodel of the aerosol infection, the airborne spread characteristics between mammalswas studied, with aim to provide the theoretical support for preventing and controllingthe outbreak and epidemic of2009(H1N1)IV among humans.Firstly, samples from suspected influenza-infected pigs were collected for viralisolation and identification and then genetic evolution of HA，NA，PB2，PB1，PA，NP，NS and M8fragments of the isolated virus was analyzed and compared with therelated A/H1N1(2009) influenza viruses using MEGA software. The results showedthat sequences of8fragments of the isolated virus revealed>99%nucleotide identitywith2009(H1N1)IV prototype strain, and its HA cleavage and receptor-binding sites were PSIQSR↓GLFGAI and190D、225D, respectively, which were identifical with2009(H1N1)IV. However, compared with HA protein of2009(H1N1)IV, mutationQ226R occurred in receptor-bing site of the isolate. Second, guinea pig aerosolinfection model were also established to verify the capacity of S-O2009IV forforming aerosols and its ability for airborne. In the model, A/swine/Shandong/07/2011can be aerosolized and infect guinea pig of infection group, but the infection rate islower than direct contact group.In conclusion, A/swine/Shandong/07/2011has the ability to form virus aerosols;and the virus can cause aerosol infection between animals under the experimentalconditions.