Prediction and Control of New Pandemic Influenza Viruses

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The H3 hemagglutinins (HA) of influenza virus isolates from domestic ducks in southern China were analyzed antigenically and genetically. The results provided molecular evidence of a role of these birds to introduce avian H3 influenza viruses to pigs as "mixing vessels" where A/Hong Kong/68 (H3N2) strain was produced.Experimental infection of pigs with H1-13 influenza A virus strains isolated from different host species provided the follwing informations ;The cells lining the upper respiratory tract of pig were susceptible not only to the HA of H3 influenza viruses of porcine and human origin but also to that of isolates from feral ducks.Genetic reassortants were produced in upper respiratory tract of pig mixedly infected with influenza viruses of duck and porcine origin.Pigs were susceptible to infection with avian influenza viruses eash know HA subtype. It is thus noted that pigs were also susceptible to H4-13 influenza A viruses which had been recognized only in avian species.Hemagglutination-inhibiting antibodies were not detected in the sera of the pigs infected with the avian influenza viruses. Antibody response was, on the other hand, clearly demonstrated in the sera by ELISA.These findings indicate that influenza viruses of other subtypes than H1-3 arepossible to be introduced into pigs and that seropidemiological survey by HI tests may not provide exact information of infection of pigs with avian influenza viruses.