Is avian influenza A (H7N9) virus staggering its way to humans?

Human infections by a new avian influenza A (H7N9) virus have been reported. As of April 23, 2013, there were 108 confirmed cases including 22 deaths in China.

Influenza protein sequences were downloaded from the Influenza Virus Resource and GISAID EpiFlu databases. Pairwise nucleotide identities were computed for assessing the evolutionary distance of H7N9 to other known avian and human viruses, and multiple sequence alignments with their position-specific entropy values were used in discussing how mutations on species-associated signature positions were introduced in the new H7N9 which may steer its way to human infection.

This report analyzed the genomic characteristics of this new H7N9 virus. Nucleotide sequence analysis clearly reveals its origin from avian viruses. In this article, we particularly focus on its internal genes that are found to derive from H9N2-another subtype of avian influenza A virus which has been circulating in birds for years. Amino acid sequences at species-specific genomic positions were examined. Although the new virus contains mostly avian-like residues at these signature positions, it does contain several human-like signatures. For instance, at the position 627 of PB2, the new virus has human-characteristic K instead of avian-characteristic E; in addition, PB2-627K, PA-100A, PA-356R, and PA-409N are also human-like signatures in the new H7N9 virus.

The new H7N9 is an avian influenza A virus; however, it does harbor several human virus-like signatures, which raises great concern that it may have a higher probability to cross species barriers and infect humans.