PLoS Pathog. 7:e1002068 (2011)2011/05/26

Highly pathogenic avian influenza A virus subtype H5N1 is currently widespread in Asia, Europe, and Africa. In particular, since 2009 Egypt has unexpectedly had the highest number of human cases of H5N1 virus infection, with more than 50% of the cases worldwide. In this study, we found that new H5 sublineages have acquired an enhanced binding affinity for human-type receptor during viral diversification in local bird populations. This is the first report identifying amino acid changes in H5 HA responsible for an increase in human H5N1 infections in an endemic area. Our findings may explain why Egypt has recently had the highest number of human H5 cases worldwide.