| The first H9 avian influenza virus was isolated from chickens in southern China in 1994, and since then it has circulated in Southeast Asia including China and many other countries worldwide for several years. However, the pandemic of H9 subtype AI, which started in summer of 1998, spread very rapidly to more than 20 provinces within several months. Since the AIVs of H9 subtype in poultry have been confirmed in worldwide, they have the characteristic of high efficiency, spread and wide range in China after 1998, and AIV of H9 subtype in human had been discoverd in 1999, it raised great concerns for its economic importance to poultry industry and potential threat to the public health. In order to investigate the molecular mechanism affecting the route of transmisson for H9N2 AIVs, strains of A/Chicken/ Shanghai /7/2 001 (62 strain) and A/Chicken / Shanghai /14/2001 (70 strain) were compared in their route of transmisson and pathogenicity. Our findings suggested that 62 strain could transmitted in chickens by direct contact,by aerosol and by fecal contact in large degree, whereas 70 only by direct contact. We also have sequenced and analysised the NA gene of 62 strain.1. Comparison of the route of transmission and the pathogenicity of 62 strain and 70 strain In order to investigate the property of transmisson and replication for H9N2 subtype avian influenza viruses, strains of A/Chicken/ Shanghai/7/2001(62)and A/Chicken /Shanghai/14/2001(70) were compared in their route of transmission and pathogenicity.62 and 70 were propagated in 10-day-old SPF embryonated chicken eggs. Allantoic fluid containing viruses was collected, examined by HI and HA tests, and stored at -70℃. The HA-and HI-positive allantoic fluids were diluted and inoculated 4 weeks SPF chickens through oral, tranasal and trachea with the dose of 200μl per chicken. Virus replication was monitored five days after inoculation. The lesion in trachea,lung of 62 was more severe than that of 70. The lesion in intestinal of 70 strain was more lower than that of 62, Virus replication was not discovered in intestinal of 70. Transmission experiments were designed. Groups of three chickens were inoculated by oral, intratracheal and intranasal routes respectively. Groups were placed in direct contact, in fecal contact, or in contact by aerosol with three uninoculated chickens. The results of virus isolation showed that, both viruses were transmitted from inoculated to uninoculated chickens by direct contact, while 62 was transmitted by aerosol , and may be in contact by fecal contact. These findings were confirmed by HI test with the sera collected from the uninoculated chickens.2. Sequencing and phylogenetic analysis of the NA gene of 62 strain Viral RNAs of 62 were extracted and RT-PCR was performed to amplify the NA gene segment with specific primer designed according to published sequences and the reference of Hoffmann.Phylogenetic analysis of NA gene of 62 was compared with those of 70 and other H9 viruses. We found that ,the homology of NA genes of 62 and 70 was 97.7%, both of 62 and 70 were in the same branch with CK/BJ/1/94 and CK/HK/G9/97, indicated that these two viruses may derive from the same ancestor. In addition to the sequence of NA of 62 published in GenBank, the highest homology of NA genes of 62 and CK/SH/2/2001 was 99.8%, the homology was 94.4% with CK/BJ/1/94, the homology was 89.9% with Q/HK/G1/97, the homology of NA genes of 62 and HK/1073/99 was 90.4%. The randome of homology of NA genes of 62 and other H9 viruses was 86.3%-99.9%, the lowest homology was 86.3% with DK/HK/Y439/97. The randome of homology of NA genes of 62 and other H9 viruses isolated in Shanghai during 1999-2002 was 94.4%-99.8%, confirmed that they were intimated in Genetic evolution. Both of them belonged to the branch of C/BJ/1/94, derived from the same ancestor virus with C/BJ/1/94 and CK/HK/G1/97.
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