Originally posted by wayno
Can someone (hopefully someone I haven't blocked ) come up with an easy explanation please? Thnx.
[edit on 11/18/2009 by wayno]
I don't know if you've blocked me or not, but here is an article that explains the basics pretty well. The last paragraph sort of explains how they
mutate by recombining with each other.
What Does H1N1 Influenza Mean?
Different Surface Proteins Make Influenza Virus Strains Different
© Kenneth Rosen
May 15, 2009
The recent outbreak of Type A H1N1 influenza has many people asking questions about the biology of influenza virus. Such as what do the letters H and
N refer to?
In the midst of all the worries and concerns relating to the recent outbreak of Type A H1N1 influenza some truly striking data about influenza viruses
in general are often forgotten. Every year in the United States more than 30,000 people die as a result of infection with “seasonal influenza”,
and more than 200,000 people require hospitalization for treatment.
The three main types of influenza virus generally differ in the severity of illness that they cause. Type A influenza is the virus that most commonly
causes the most severe flu symptoms, while Type B is weaker and Type C is the weakest of all, rarely causing any symptoms.
What Do the H and the N Mean in the Name of the Virus
Influenza viruses can be identified based on the chemical structure of specific proteins found on the outer surface coat of the virus particle. The
two dominant proteins found on the virus surface are known as Hemagglutinin (often referred to as “H” or “HA”) and Neuraminidase (“N” or
“NA”). Both of these proteins play critical roles in the lifespan of an influenza virus.
The array of flu viruses that have been characterized over the years can carry different versions of H or N, and thus the numbering system. There are
more than 10 known forms of H and as many as 9 versions of N. Thus different strains can be characterized by the type of H or N that they carry e.g.
H1N1, or H3N2, etc. The avian flu that focused the world’s attention several years ago was known as H5N1.
What Do the H and N Proteins Do?
The H protein is important in allowing the virus to adhere to cells and gain entry so that the virus can be replicated. The name “hemagglutinin”
means that the protein can cause red blood cells to clump together, one of the features originally associated with the flu virus when tested in
laboratory dishes. The N protein, “neuraminidase”, is an enzyme that helps the virus to escape from cells once new viral particles have been
replicated. This enzyme can cleave specialized sugar molecules that are often associated with the proteins found on the surface of cells. This is the
protein that is targeted by flu medications such as Tamiflu and Relenza.
Flu Viruses Can Change Quickly
Unlike many other viruses, the nucleic acid that is found inside the influenza virus family is RNA not DNA, making them “RNA viruses”.
Additionally, the instructions for making a new virus are carried in 8 separate fragments of RNA and not in one large contiguous piece of DNA as is
true for many other viruses like chickenpox. The presence of the multiple fragments means that if a cell is infected simultaneously with two different
versions of influenza, the fragments can be shuffled to generate a new form.