Antigenic Variants of Influenza A/H3N2 Viruses
Uh, I thought you just did. ;^)
Someone correct me if I'm wrong, but isn't the recommended annual flu shot a combination of three inactivated influenza viral types thought to be most likely coming from the Far East each year, and isn't the HxNx nomenclature for for Influenza Type A subtypes?
Do Influenza Types B or C have variations of the Hemagglutinin or Neuraminidase enzymes on their capsid coats? I'm just a humble FP.
Antigenic Variants of Influenza A/H3N2 Viruses
Influenza viruses belong to the orthomyxovirus family and consist of types A, B, and C. These medium-sized (80 to 120 nm), enveloped, single-stranded RNA viruses contain eight gene segments (seven for influenza C).
The segmented nature of the genome allows reassortment of RNA segments between two influenza viruses during dual infection and facilitates antigenic variation.
Surface glycoprotein spikes possess either hemagglutinin or neuraminidase activity.
Hemagglutinin mediates cell attachment and fusion of virus and cell membranes. By cleaving terminal sialic acid residues and destroying the receptors recognized by hemagglutinin, neuraminidase promotes release of virus from infected cells and spread within the respiratory tract.
Influenza C viruses have seven gene segments and lack a neuraminidase.
The surface glycoproteins induce host humoral and cellular immune responses and are responsible for the changing antigenicity of influenza viruses.
Two major types of antigenic change can occur: drift and shift. Antigenic drift refers to relatively minor changes in hemagglutinin and, less often, neuraminidase antigenicity that occur frequently (usually every few years) and sequentially in the setting of selective immunologic pressure in the population. Drift results from point mutations of the corresponding RNA segment.
Antigenic shift occurs only in influenza A viruses and results from acquisition of a new gene segment for hemagglutinin with or without one for neuraminidase.
This may occur through genetic reassortment during dual infections with human and animal influenza type A viruses; by the reintroduction of a virus that has not circulated recently in the human population; or by direct transmission to humans of an animal influenza virus that is capable of efficient human-to-human transmission.
MA