How worried should we be about avian flu?
The Briefing Room
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Bird Flu Viruses
Bird flu is a disease that birds get and it's caused by an influenza virus, really a very similar virus to the viruses that cause flu in people. All human influenza viruses were once viruses in birds and at some point they crossed over from birds into humans. Why is it that all flu viruses tend to start in birds? Well viruses are what we call obligate intracellular parasites. They have to get inside a bird or a human, a host and replicate.
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