Introduction
Pigs are important hosts for influenza A viruses. Based on the surface antigens hemagglutinin and neuraminidase, influenza virus strains that are enzootic in swine populations worldwide are assigned to the subtypes H1N1, H3N2, or H1N2. Infection by other subtypes, e.g. H3N1, H4N6, H5N1 and H9N2 has been observed but they have not been maintained in pigs as independent lineages. Natural infections of pigs by influenza viruses from different hosts, e.g. by avian virus strains, have been reported [1–3]. It has been shown that infection of pigs with heterologous virus resulted in lower virus yields that failed to transmit infection to other pigs [4]. Though natural infections by avian influenza viruses were rarely able to establish a stable lineage
in pigs, they may allow the introduction of new gene segments by
genetic reassortment in host cells infected with two viruses.
Introduction
Pigs are important hosts for influenza A viruses. Based on the surface antigens hemagglutinin and neuraminidase, influenza virus strains that are enzootic in swine populations worldwide are assigned to the subtypes H1N1, H3N2, or H1N2. Infection by other subtypes, e.g. H3N1, H4N6, H5N1 and H9N2 has been observed but they have not been maintained in pigs as independent lineages. Natural infections of pigs by influenza viruses from different hosts, e.g. by avian virus strains, have been reported [1–3]. It has been shown that infection of pigs with heterologous virus resulted in lower virus yields that failed to transmit infection to other pigs [4]. Though natural infections by avian influenza viruses were rarely able to establish a stable lineage
in pigs, they may allow the introduction of new gene segments by
genetic reassortment in host cells infected with two viruses.
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