Rapid evolution of H5N1 influenza viruses in chickens in Hong Kong

The H5N1 avian influenza virus that killed 6 of 18 persons infected in Hong Kong in 1997 was transmitted directly from poultry to humans. Viral isolat es From this outbreak may provide molecular clues to zoonotic transfer. Her e me demonstrate that the H5N1 viruses circulating in poultry comprised two distinguishable phylogenetic lineages in all genes that were in very rapid evolution, When introduced into new hosts, influenza viruses usually under go rapid alteration of their surface glycoproteins, especially in the hemag glutinin (HA). Surprisingly, these H5N1 isolates had a large proportion of amino acid changes in all gene products except in the HA. These viruses may be reassortants each of whose HA gene is well adapted to domestic poultry w hile the rest of the genome arises from a different source, The consensus a mino acid sequences of "internal" virion proteins reveal amino acids previo usly found in human strains. These human-specific amino acids may be import ant factors in zoonotic transmission.