Phylogenetic Analysis And Infectivity Evaluation To Mammalian Of H9N2 Avian Influenza Virus

There were five influenza pandemics in the past one hunderd years, but fourth of them were caused by the lower pathogenicity influeza A viruses with several avian influenza virus gene segements.Therefore we should aslo pay attention to the low pathogenic influenza viruses widespreadly in the animals. H9 subtypes of influenza virus are being monitored by WHO because they possess the possibility to cause the next influenza pandemic in the crowd. In recent years, H9N2 subtype avian influenza virus has evolved into three lineages. Hence we performed the phylogenetic analysis of four H9N2 iosolates from Jilin and Shandong province and explored the infectivity of the H9N2 virus in cat, dog, pika, and guinea pig respectively. Furthermore, we evaluate the transmissibility of four H9N2 viruses in guinea pig model.H9N2 subtype avian influenza virus has evolved into three lineages, including the CK/bei-like strain, Gl-like virus and korea-like strain. CK/bei-like strains has spreaded widely in China since 1994 and been divided into two sublineages with the respectively representative strains, A/Quail/Shantou/1038/02 and A/Chicken/Shanghai/F/98 (Ck/SH/F/98). HA genes of four H9N2 virus isolates from Jilin and Shandong have been analyzed. A/ Chicken/Shandong/Li-1/2009 (CKSD/1) and A/Chicken/Jilin/Hu-3/2006(H9N2) (CKJL/1) were belong to CK/bei-like strain and the former was closer to A/Chicken/Shanghai/F/98. A/Chicken/JN/Li-2/2010 (H9N2) (CKJN/1) and A/Chicken/JN/Li-3/2010 (H9N2) (CKJN/2) were very closely in the phylogenetic tree. But they were belong new lineages. The result indicated that HA genes of H9N2 subtype avian influenza virus are changing rapidly.To explore the ability of H9N2 subtype avian influenza virus to infect mammals, dogs, cats and pikas were infected with H9N2 virus. Dog, cat and Pika had no visible clinical symptoms during 14-day observation period. Body temperature, appetite and feces were all normal. Three kind of animal could be infected by H9N2 virus by intranasal. The results of virus titration show that the virus could replicate in the respiratory tract with the titers rang of 0.75～5.751gEID50/ml.To evaluate transmissibility of H9N2 subtype avian influenza virus in mammals, the guinea pigs were used as mammal to evaluate replication and horizontal transmission capacity of the four H9N2 viruses. We found that all four viruses could replicate well in turbinate but CKSD/1 and CKJN/1 could replicate well in tracha of the guinea pigs than CKJN/1 and CKJN/2 did. The virus in nasal wash of inoculated group could be detected during p.i.2 day-p.i.8 day in transmission experiment. But the transmission only has take place in CKJN/1 contact group.Our results indicated that H9N2 subtype avian influenza virus has became different lingage and the virus has been acquired the ability to replication in mammal. And it has potential(潜在的) possibility to aquire transmibility among mammals.