A recent study in this journal identified three H5 highly pathogenic avian influenza A viruses (HPAIVs) with differing NA subtypes (N1, N6 and N8) and revealed that while the three isolates were all highly pathogenic in chickens and ducks only the H5N1 and H5N6 subtypes showed high pathogenicity in mice, with no mortality observed for H5N8.1 This suggests differences in their pathogenicity potential. Since the emergence of H5N1 in China in 1996, it has continued to evolve and reassort with other NA subtypes, including N2, N6, and N8.