The study of the virus H1N1 showed that its constitution is unique because of its structure and its genetic characteristics. It has a spherical shape from 20 to 300 nm. It contains mRNA, which is divided into eight segments. They replicate individually and stay independent during the multiplication. The virus is also made of two glycoproteins: hemagglutinin (HA) and neuraminidase (NA), visible on the surface of the virus. They play a very important role in the biological properties. Hemagglutinin enables the virus to hook on the cell receptor. Moreover, it allows the melting between the virus envelop and the cellular membrane. NA is the swelled part in hammer on the virus. It enables to cut the virus when it of from the cell when it can't enter the cell, and also the separation of the new virus. These are essential molecules for the virus because thanks to them, it can hook, contaminate and multiply itself. They are the virus bases. The virus is also made of intern proteins which ensure the virus cohesion and its replication. Besides, there are no structural proteins.

The virus replication can be divided into several steps. Firstly, the virus hooks on the cell receptors. Then, both membranes melt together, therefore the virus can enter the cell. Secondly, in the nucleus, there is a primary transcription of the RNA. The replication leads to the production of proteins and RNA in a sufficient amount to create a new virus generation. Finally thanks to the budding, spherical particles appear. A cell can produce thousands of entire virions; once it has secreted this amount of virus, it is exhausted and so dies slowly.

The Spanish flu was very contagious and lethal, although it didn't directly lead to death, but weakened immune defences. It has been the biggest pandemic in human history, more serious than plague. Scientists think that pandemics are periodical: they occur approximately every forty years. H5N1 bird flu strain, spreading through Asia has some common features with the 1918 strain. But so far it has not been able to easily pass on from human to human. That’s why we can wonder whether H5N1 will be the next pandemic.

Bibliography

• www.ibiblio.org/hyperwar/AMH/XX/WWI/flu/philflu/philflu.html
• www.dinosoria.com/grippe_espagnole.htm
• http://en.wikipedia.org/wiki/Spanish_flu
• http://virus.stanford.edu/uda/

Iconography

• www.pandemic.info/about_bird_flu/h5n1.htm
• www.ibiblio.org/hyperwar/AMH/XX/WWI/flu/philflu/philflu.html
• www.wisconline.com/feature/flu_images.html
• www.dinosoria.com/grippe_espagnole.htm
• http://en.wikipedia.org/wiki/Spanish_flu

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