Influenza A Hemagglutinin H1 (A/Brisbane/59/2007) (H1N1)

Influenza A virus is a major public health threat, killing more than 30,000 people per year in the USA (1). Novel influenza virus strains emerge periodically to which humans have little or no immunity, resulting in devastating pandemics. Influenza A can exist in a variety of animals; however it is in birds that all subtypes can be found (2). These subtypes are classified based on the combination of the virus coat glycoproteins hemagglutinin (HA) and neuraminidase (NA) subtypes. During 1997, an H5N1 avian influenza virus was determined to be the cause of death in 6 of 18 infected patients in Hong Kong (3). There was some evidence of human to human spread of this virus, but it is thought that the transmission efficiency was fairly low (4). Although it has been known that cleavage site and glycosylation patterns of the HA protein play important roles in determining the pathogenicity of H5 avian influenza viruses, it has only recently been shown that an additional glycosylation site within the globular head of the NA protein also contributes to the high virulence of the H5N1 virus (5)