Double Infections with Avian A/H5N1 and Swine A/H1N1 Influenza Viruses in Chickens

The rapid outbreak of the highly pathogenic A/H5N1 avian influenza virus among domestic birds and its transmission to humans have induced world-wide fears of a new influenza pandemic. If a human-trophic strain of A/H5N1 is replicated in domestic animals, it might have high transmissivity and pathogenicity to humans. If the misassembling of both avian and swine influenza viruses occur in the same cells in domestic fowl, novel pandemic infections among humans might emerge due to human-fowl contacts. In the present study, examinations of mixed infections with A/H5N1 and A/H1N1 viruses were carried out using living chickens to elucidate the possibility of chimeric avian-swine influenza virus replication in domestic fowl. The sporadic strains of avian A/H5N1 and swine A/H1N1 viruses were co-infected into embryonated eggs and post-hatched chickens. A double staining method using the anti-A/H5N1 and anti-A/H1N1 antibodies indicated that A/H5N1 and A/H1N1 viruses were co-localized in the same cells in the chorioallantoic membrane of embryos, and in the lungs of chickens challenged by the double infections. This indicated that the avian influenza and swine influenza viruses might be assembling in the same cells of chickens, and chimeric viruses containing the characteristics of both viral strains might appear.