Abstract:To isolate influenza type A H1N1 virus by using chicken embryo inoculation and to characterize its biological properties in order to provide a scientific basis to establish the preventive measures,the respiratory specimens were inoculated into the allantoic cavity of developing chicken embryo for virus propagation and the viral titer was measured by hemagglutination (HA) assay. The sub-type specificity of virus was determined by reverse transcription PCR (RT-PCR). Formaldehyde was used to inactivate the virus isolated from chicken embryo and the effect of inactivation of virus was evaluated by chicken embryo inoculation method. The immune response profile following viral infection was analyzed by hemagglutination inhibition (HI) test for both acute and convalescent phase sera of the confirmed cases. It was found that 12 strains of influenza type A H1N1 virus were isolated from 13 respiratory specimens of the clinically confirmed cases,and most of which was isolated at the second passage with lower HA-titers ranged from 1∶1 to 1∶16. Moreover,the HA titer of the viral isolate was not increased dramatically at second passage in chicken embryo. Compared to chicken or human "O" erythrocytes,the guinea pig erythrocytes were proved to be more sensitive when the HA titer of isolate was measured. The 1‰ formaldehyde could completely inactivate the virus within 24 hours,and simultaneously,the viral HA titer lost dramatically. The HI titer in convalescent phase sera showed a 2 to 16-fold increase in comparison with that in the paired acute phase sera,but the 4-fold increase in HI titer required approximately a period of 3 weeks. It is evident that the chicken embryo inoculation method can be applied for the isolation of influenza type A H1N1 virus,but the HA titer of the isolates is lower. Although formaldehyde can rapidly inactivate the virus isolated,the HA titer of viral antigen after inactivation is difficult to maintain at a high level. The production of the specific HA antibody is rather slow with lower titer. For the local laboratory,it is better to use guinea pig erythrocytes to detect the viral HA titer.
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