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  • Title: [Molecular mechanism affecting route of transmission for H9N2 subtype AIV].
    Author: Shi HY, Liu XF.
    Journal: Wei Sheng Wu Xue Bao; 2006 Feb; 46(1):48-54. PubMed ID: 16579464.
    Abstract:
    The available evidence suggests that H9 subtype avian influenza virus (AIV) did not circulate in Chicken flocks in China until the early 1990s. However, the pandemic of H9 subtype AI, which started in summer of 1998, spread very rapidly to more than 20 provinces within several months. Obviously, the virus responsible for the 1998 pandemic was quite different from the virus isolated in early 1990s. In order to investigate the molecular mechanism affecting the route of transmission for H9N2 AIVs, strains of A/Chicken/Guangdong/SS/94 (H9N2) (SS) and A/Chicken/ Shanghai/F/98 (H9N2) (F) were compared in their route of transmission. SS strain representing the earlier strain was isolated in chickens in Guangdong province in 1994, whereas F strain was isolated in Shanghai during 1998 pandemic. The findings suggested that F strain could transmitted in chickens by direct contact and by aerosol route. Whereas SS strain only by direct contact, and neither of two viruses by fecal contact. The cDNAs derived from the HA and NA genes of SS strain were cloned into vector pHW2000 to construct two transcription/expression plasmids respectively, and the cDNAs derived from 8 genes of F strain was done in the same way. Three recombinants were generated by reverse genetics: RF7/SSHA with the HA gene from SS strain and the remaining seven genes from F strain, RF7/SSNA with the NA gene from SS strain and the remaining seven genes from F strain, and RF7/SSHA/SSNA with the HA and NA genes of SS strain and the remaining six genes from F strain. In order to identify three recombinants, a total of seven genes from them were amplified by using PCR with universal primer pairs of H9N2 influenza virus and sequenced. In addition, three recombinants were characterized by HA and HI tests and sequence analysis. The results indicated that three recombinants were successfully rescued by reverse genetics. To determine the genes associated with the ability to transmit by aerosol route in chickens, a set of transmission experiments were designed. Groups of three chickens were inoculated with equal dose of virus by oral, intratracheal and intranasal routes. Each group was placed in direct, aerosol or fecal contact with three uninoculated chickens. Virus isolation and identification showed that only the RF7/SSHA recombinant was transmitted from inoculated to uninoculated chickens by aerosol route, whereas three recombinants were transmitted by direct contact, but not by fecal contact. The results were further confirmed by HI test of serum samples from uninoculated chickens. The data suggest that the NA gene might be the major determinant of the ability of aerosol transmission for H9N2 subtype AIVs in chickens.
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