Evolution

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Evolution
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The Evolution of the Flu Virus

The flu virus has can rearrange its RNA by mixing with other flu viruses to create hybrid viruses that have new antigens in the same virus. These viruses are like completely "new" flu viruses because nobody has any antibody memory against them.

These viruses cause pandemics of influenza. This happens when the flu virus from two different species infect the same cell.

Flu viruses tend to be species-specific. There are human, horse, pig, chicken, and duck flu viruses. Ordinarily they will not cross-infect. But, if a human is in close contact with one of these animals when the animal has their flu, sometimes the virus can infect the human lung.

If a human also has a human flu virus infection at the same time as an animal flu virus, the two can replicate in the same cells at the same time. The viruses that come out of this cell have their RNA molecules rearranged and some of them might be mostly human influenza but with animal flu antigens on their surface. This is a big change, or antigenic shift in the virus. The chances of this happening is very remote, but over time it does happen.