The current influenza type A virus H1N1 is called "swine flu" because it contains genetic material that is similar to that found in influenza viruses that infect pigs. However, swine flu did not arise from pigs and cannot be "caught" from pigs. The name "swine flu" quickly caught on through the media, though it is misleading.
How Does the Influenza Virus Mutate?
Influenza viruses contain a considerable variety of genes which allows them to mutate easily and frequently. This makes it difficult for the body’s immune system to recognize each new mutant virus form and be ready to attack an infection. A lot of time and lab tests by researchers are required to identify a new virus and manufacture the vaccine against it.
For this reason, immunization against the H1N1 flu is not yet widely available and because it is a new flu virus, no one will have immunity against it unless they have been already been infected or received swine flu immunization.
What is Type A Influenza?
There are three classes of influenza virus: A, B and C. All three types can affect humans but only type A is the one that is responsible for epidemic illness. For this reason, the current influenza virus is called influenza type A H1N1 or A/H1N1. The letters H and A refer to the important defining glycoproteins that exist on the surface of the outer envelope of the virus.
"H" stands for the molecule hemagglutinin, which attaches the virus to the cell it is entering and hence infecting. This molecule is used to make antiflu vaccines. "N" stands for neuraminidase, which is an enzyme that allows the virus to "eat and digest" their way inside cells and later to release newly synthesized viruses. The antiviral medications Tamiflu and Relenza work by inhibiting this important enzyme.
The Flu Virus Mutates
The hemagglutinin molecule comes in 16 forms, which is useful for new virus forms such as H1N1 to get past the immune system without being recognized. Similarly, neuraminidase has nine different structural forms. Hence H1N1 has form one of each molecule, while the virus that was responsible for the 1957 flu epidemic was called H2N2 and had form two of each. However, only three combinations of H and N have been found in influenza viruses that infect humans.
Other parts of the virus genome can also alternate to help with variability and the greater the mutation the more likely that it will be a new virus that can cause a great deal of harm because no one has immunity to it yet.
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Reference
Watts, Geoff: 2009 A/H1N1 Influenza Virus, The Basics. British Medical Journal 339:368-339
Noreen Kassem - Noreen Kassem is a hospital doctor based in London, UK. She has extensive experience in clinical research and an undergraduate honors ...
