Chemistry

Influenza viruses and their nomenclature

Influenza viruses and their nomenclature



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Today, a distinction is made between three serologically different types of influenza virus, some of which are quite different, and are summarized in the following table:

Tab. 1
Influenza typeEpidemics / pandemicsAntigen variationsCourse of the disease
Influenza AMost common cause of epidemics and pandemicsConstant small variations of the surface antigens hemagglutinin (HA) and neuraminidase (NA) antigenic drifts; larger variations every approx. 10 to 15 years antigenic shiftsOften severe disease
Influenza BCan also cause epidemicsOften there are small variations in HA and NA antigenic drifts; so far noneantigenic shifts observedMostly milder disease courses than with influenza A.
Influenza CVery rarely causes disease in humansNot knownMild disease courses

By anitgenic driftsthat lead to small structural changes in the surface antigens hemagglutinin (HA) or neuraminidase (NA), new variants of the virus types influenza A and B are created. Antigenic shiftsthat lead to major structural changes in HA or NA create new subtypes of the influenza A virus type.

Each by one antigenic shift The resulting new HA and NA molecule is given a new number. The earliest influenza virus for which the structure of the HA and NA molecules could be determined was the causative agent of the Spanish flu of 1918/1919 (although the structure was of course not determined much later). Its surface antigens were named H1 (hemagglutinin) and N1 ( Neuraminidase).

To date, fifteen hemagglutinin subtypes (H1 to H15) and nine neuraminidase subtypes (N1 to N9) have been identified. In principle, any HA / NA subtype combination is conceivable, i.e. 135 combinations. In humans, however, only the influenza A subtypes H1N1, H2N2 and H3N2 with a large number of variants have so far been observed. In addition, a few people in Hong Kong were infected with the H5N1 subtype in 1997.

All influenza viruses recorded and characterized by the ISS (International Influenza Surveillance System) are given their own designation such as:

  • A / Sydney / 5/97 (H3N2)

or

  • B / Beijing / 184/93

The first letter indicates the virus type. This is followed by the location of the first isolation, a serial number assigned by the WHO and the year of the first isolation. In the case of influenza A viruses, the HA / NA subtype combination also follows in brackets.

Literature

(1997):The human influenza viruses. In: Molecular Virology.S.ModrowD.Falke (Ed.). Spectrum Academic Publishing House, 253-259
Schmidt, M. (1999):Influenza Shot - The Time Is Now!. In: PTA today. 13, 901-907