Thursday, May 21, 2009

What's H1N1, Anyway?

The recent swine flu virus has been characterized as “H1N1” and if you remember a few years ago, the bird flu was caused by an “H5N1” virus. So what do the H and N mean, and why the different numbers? All influenza viruses have the proteins hemagglutinin (H) and neuraminidase (N) on their surfaces, or outer coating. Hemagglutinin is involved in virus binding to host cells, aiding in the initial step of virus entry into the cells it infects. Once a virus gains access to a cell, it uses the host cell’s machinery to replicate itself, leading to the production of more infectious viruses. Newly replicated viruses need to be released from the host cell so they can continue with more rounds of infection, so neuraminidase acts as an enzyme which helps in this release process. In fact, neuraminidase inhibitors, such as Relenza and Tamiflu, are often used to treat flu.

The protein structure of both H and N differ from one influenza virus strain to another, so the numbering system corresponds to the form or version of the protein on a given virus. In humans, three H and two N subtypes are found, indicating that the swine flu virus carries subtype 1 of the H protein and subtype 1 of the N protein on its surface. By determining the subtypes of H and N on a given virus, we can anticipate its virulence and potential impact by comparing it to viruses we have seen in the past with the same or similar protein makeup.

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