How the flu virus turns killer
                                                    
   Lead researcher Dr Yoshihiro Kawaoka, of the University of
   Wisconsin-Madison, US, said: "Because the influenza virus
   constantly mutates, and because only a few changes can make
   a non-pathogenic virus highly pathogenic, we should assume
   that an outbreak of any new strain or subtype is potentially
   dangerous to humans." 

   Natural reservoirs 

   Wild waterfowl are natural reservoirs for the influenza virus.
   These birds transmit the virus to pigs or chickens, which then
   pass it on to people. 

   The deadly outbreak of influenza virus subtype H5N1 in Hong Kong
   in 1997 was the first documented case of an influenza virus 
   jumping directly from chickens to people. 

   Dr Kawaoka and his team obtained samples of the H5N1 viruses that
   had infected Hong Kong residents. Testing these viruses in
   laboratory mice, the researchers found that they had the same 
   impact on mice. 

   Just two particles of the deadly form of the virus isolated from
   human victims were enough to kill a mouse. 

   The research is published in the journal Science.

   Thursday, 6 September, 2001, 23:04 GMT 00:04 UK 
   http://news.bbc.co.uk/hi/english/health/newsid_1528000/1528226.stm
   --------------------------------------------------

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