Influenza A virus subtype H5N1

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Influenza A virus subtype H5N1 (A/H5N1) is a subtype of the influenza A virus, which causes influenza (flu), predominantly in birds. It is enzootic in many bird populations, and also panzootic. A/H5N1 virus can also infect mammals which have been exposed to infected birds; in these cases symptoms are frequently severe or fatal.

The N in H5N1 stands for "Neuraminidase", the protein depicted in this ribbon diagram

Transmission electron micrograph (TEM) of negatively stained Influenza A virus particles (small and white) attached to host cells (large and irregular) (late passage). (Source: Dr. Erskine Palmer, Centers for Disease Control and Prevention Public Health Image Library)

Influenza A virus

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Influenza A virus (IAV) is a pathogen that causes the flu in birds and some mammals, including humans. It is an RNA virus whose subtypes have been isolated from wild birds. Occasionally, it is transmitted from wild to domestic birds, and this may cause severe disease, outbreaks, or human influenza pandemics.

Influenza A virus

A transmission electron micrograph (TEM) of the reconstructed 1918 pandemic influenza virus. The bottom structure represents membrane debris from the cells used to amplify the virus. Pictured are the 'elliptical' particles representing the smallest particles produced by influenza virus. Purification techniques often deform the particles without proper fixation protocols, leading to 'spherical' appearance. Filamentous or intermediate sized particles simply extend along the long axis on the opposite side of the genome segments.

Genetic evolution of human and swine influenza viruses, 1918–2009