CHARACTERIZATION OF A NOVEL INFLUENZA HEMAGGLUTININ, H15 - CRITERIA FOR DETERMINATION OF INFLUENZA-A SUBTYPES

Two viruses with a novel hemagglutinin (HA), A/duck/Australia/341/83 a nd A/shearwater/West Australia/2576/79, have been isolated from a duck and a shorebird in Australia. Hemagglutination inhibition and double immunodiffusion assays failed to reveal cross-reactivity with any of t he known subtypes (H1 to H14). We therefore propose that these viruses constitute a new HA subtype, H15. Sequence analysis of the HA genes c onfirmed the serologic findings. When compared at the amino acid level , the HA1 region of the H15 subtype differs from those of the other su btypes by 30% and more, This degree of heterogeneity is also found amo ng HA genes of other subtypes. Thus we propose that amino acid sequenc e data should be evaluated when determining the HA subtypes of influen za A viruses. Sequence comparison and phylogenetic analysis suggested that the HA subtype H15 is most closely related to the H7. Compared to the H7 HA, the H15 acquired a 30-nucleotide insertion within HA1 at p osition 253 which is located in the globular head of the molecule. Thi s finding suggests that RNA recombination, although a rare event in na ture, may play an important role in the evolution of influenza viruses . (C) 1996 Academic Press, Inc.