World’s First Case of Bird Flu In China

Influenza comes in three basic types: A, B, and C. The second two — influenza B and influenza C don’t cause big problems.
The trouble-makers are the influenza A strains. Among other things, influenza A viruses prefer hemagglutinin and neuraminidase. Hemagglutinin (H) and neuraminidase (N) are little protein spikes on the flu’s surface that help it invade cells. There are 16 versions of hemagluttinin and nine for neuremanidase.

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There are 144 different subtypes of influenza A: from H1N1 to H9N16.
All of them exist in wild birds around the world, so they are all bird flu. But every now and then, one evolves the ability to infect other animals.

H1N1 is one of the more promiscuous. It can infect birds, people, pigs, and horses. H2N2, on the other hand, only makes its way into people and birds.

Why Are There so Many Types of Bird Flu?

Scientists call it reassortment. When a bird gets infected with two viruses: H1N1 and H2N2 the two viruses reproduce inside the bird’s cells, H1N1 can grab accessories from H2N2. This creates a new strain that looks like H2N2 but can now infect people (because it started off as just H1N1).

That’s what happened in 1957 during the Asian flu pandemic, says computational biologist Richard Goldstein, from the National Institute for Medical Research in London.
Since H2N2 had never infected people before, our immune systems had never seen these accessories and thus, we had little defense against it. The new strain ended up killing roughly 70,000 Americans.

Scientists are still trying to figure out H7N9.
So far, it looks like the virus got its H from ducks, its N from migratory birds and other genetic material from chickens.

Source: Medindia