Abstract
The H5N1 influenza A virus that is currently circulating in Asia, Africa and Europe has resulted in persistent outbreaks in poultry with sporadic transmission to humans. Thus far, it is believed that H5N1 does not possess sufficient ability for human-to-human transmission and subsequent pandemic infection. Both receptor binding specificity and virus infectivity are key factors in determining whether influenza A virus becomes pandemic. The use of human viral isolates in various studies has helped to illustrate the changes in receptor binding specificity and virulence as a result of adaptation in humans. In this review, we highlight the important amino acids and domains of viral proteins related to receptor binding specificity that have been reported for humans and avians using mammalian models. Thus, this review will consolidate findings from studies that have shed light on the receptor binding and transmission characteristics of the H5N1 influenza virus, with the goal of improving our ability to predict the transmission efficiency or pandemic potential of new viral strains.