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Keith Robison robison at nucleus.harvard.edu
Mon Jul 10 14:54:43 EST 1995

S. Frog (darcoda at telerama.lm.com) wrote:

: 	Hello.  I'm not sure if this is the proper group to ask this 
: question, and if it isn't, I apologize, but I have a question about the flu.
: 	Yes, the common old flu.  First of all, is it a retrovirus?  


: Second, if it isn't, then I think my definition of a retrovirus is wrong, 
: so could someone please explain it?

Retroviruses are viruses with
	1. an RNA genome
	2. which create DNA copies of their RNA genome as part
	   of their replication process.

Flu virus doesn't make a DNA copy, and so isn't a retrovirus.

: 	Thirdly, I heard somewhere (don't ask me where) that the flu is 
: only around a hundred thirty years old, and it mutated from some other 
: virus.  Thus the high casualty rate when it first hit right after world 
: war I.  Is this true?

Not quite.  Flu virus' genome is carried on multiple molecules of
RNA (8, I think).  If two different flu-like viruses infect the same
cell, then that cell can generate new flu viruses that contain
some mixture of the two input viruses  i.e., if we call the 
8 segments 1-8 and the 2 strains A & B, then you can get working
viruses from any drawing such as 1a,2b,3b,4b,5a,6a,7b,8a etc.
It's this periodic reassortment between flu-like viruses (I
think its human and avian ones) which leads to radically different
flu viruses -- which in turn cause epidemics because they are so
different from what the human population's immune system has seen.

Keith Robison
Harvard University
Department of Cellular and Developmental Biology
Department of Genetics / HHMI

robison at mito.harvard.edu 

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