Influenza viruses consists of three types (Influenza A, B, and C), which make up three of the five genera in the Orthomyxoviridae family. Commonly know as the flu, influenza strains can affect both birds and mammals.
Influenza strains form roughly spherical particles and are similar in composition with viral envelope containing two main types of glycoproteins (hemagglutinin and neuraminidase), wrapped around the central core of the viral RNA genome and other viral proteins that package and protect the RNA.
Unusually for a virus, the influenzavirus genome is not a single piece of nucleic acid; rather a seven to eight segmented fragments of negative-sense RNA with each fragment expressing different viral proteins. Influenza spreads seasonally, resulting in about three to five million yearly cases of severe illness and about 250,000 to 500,000 deaths annually or into the millions in pandemic years.
flu hemagglutinin; H3N2 HA; H3N2 hemagglutinin; Influenza H3N2; influenza hemagglutinin