A new study suggests that bird flu is becoming more dangerous each year. 

 Scientists in China and the US injected mice with samples
 of avian flu virus which emerged in different years. 

 They found that the newer forms of the virus kill more
 rapidly than their predecessors. The fear is that this
 will increase the risks to humans too. 

 The researchers, whose work is reported in Proceedings
 of the National Academy of Sciences, say more action is
 needed to try to curb the spread of the virus. 

 Earlier this year a strain of bird flu called H5N1 killed
 23 people in east Asia - the most in any year since the
 strain first emerged seven years ago. 

 Now scientists have found evidence that it is mutating in
 ways which make it more lethal. 

 They took 21 different samples of H5N1 isolated over the
 years since 1997, and injected them into mice. 

 A strong pattern emerged - the most recent viruses kill
 the mice much faster - which would suggest bird flu is
 also becoming more lethal to humans. 

 However, as Professor Robert Webster, from St Jude
 Children's Research Hospital in Memphis, US, points out,
 it has not yet acquired the most dangerous mutation. 
 He said: "The thing that's lacking so far in these
 viruses is the ability to transmit human to human. 

 However, other mutations remain a mystery. Professor
 Webster believes the mutations may be caused by the
 virus jumping from species to species. 

 As well as becoming more lethal, H5N1 is also now able
 to reproduce in more parts of the body than before. 
 The trend towards more dangerous forms of the virus is
 one which the researchers believe will continue. 

 Sudden change 
 The concern is that the virus will eventually accumulate
 enough genetic changes to become good at passing between
 humans. 

 Even more of a concern would be the sudden change that
 could be caused should the flu combine with a human flu
 in someone's body. 

 The two viruses could swap genes and create a potent
 hybrid as deadly as the bird strain and as contagious as
 a regular human strain. 

 Professor Webster, who runs a World Health Organization - 
 affiliated laboratory studying animal diseases, believes
 the international community needs to put more resources
 into tracking bird flu if a major epidemic is to be avoided. 

 The avian flu has forced authorities to slaughter millions
 of chickens and other fowl in Asia to stem outbreaks in 
 recent years

 http://news.bbc.co.uk/1/hi/health/3849127.stm


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