What’s in a name? H5N1 and H1N1 Explained

Bird Flu is also known by the snappy nickname of H5N1. What do those letters and numbers mean? Put simply they represent a means to identify and differentiate the various Influenza viruses out there


Letters and Numbers:

The H (as in H5) stands hemagglutinin and the N (As in N1) for neuraminidase. These two identifiers are proteins found on the surface of the virus. Hemagglutinin has 15 different subtypes while neuraminidase has 9 different subtypes. This allows a differentiation between different strains. All types of Influenza are found in birds and several have the ability to affect humans.

So what the big deal?

Influenza can change itself over time by one of two ways. The first known as "antigenic drift." Occurs when small changes in the virus occur over time. As with any recording you almost never get it 100% perfect. If enough of the virus is changed, the antibodies it has produced may not recognize the drifted virus and thus the body may be prone to being infected again. The other method is known as "antigenic shift." Antigenic shift occurs rapidly and marks a major change in the makeup of the virus with new combinations of hemagglutinin and neuraminidase found on the surface. The body seldom has a defense against this, but it fortunately is a rare occurrence.

Bad Boys From Past Pandemics

1918-19, "Spanish flu," Influenza A H1N1
1957-58, "Asian flu" Influenza A H2N2
1968-69, "Hong Kong" Influenza A H3N2


Material taken from The CDC's website

[edit on 10/4/05 by FredT]

[edit on 10/4/05 by FredT]

[edit on 10/4/05 by FredT]

[edit on 4/26/09 by FredT]

Aw, come on FredT....

You gotta also include "recombination" as a possible method of novel flu creation.

For those of you who don't know the difference...

Viruses are generally thought to evolve via shifting and drifting. Shifting occurs when viruses swap genes and drifting was thought to be due to a steady accumulation of mutations.

However, rapidly evolving viruses simply recycle old mutations via "recombination".




[edit on 4-10-2005 by gman55]

Thought this would be relevant given the swine flu outbreak.

Hey FredT,

Long time since I posted here...knew I would return when the event started again...seems strange to hear the H1N1 designation for this new swine/avian/human virus since that was the same one in 1918-19 abit with different genome structures.

Later,

Gman55

reply to post by gman55


Yeah I looked at that too. When i get some time I will do some digging and see if I can find more info.