A precis of current SARS outbreak from the NS
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Super-fit bird flu evolved in China
newscientist.com
18:27 07 July 04
NewScientist.com news service
The bird flu that ravaged east Asian birds earlier in 2004, and killed 23 people, is a super-fit mutant that evolved in southern China, reveal scientists. It emerged in ducks and chickens over the past two years, they say.
The Chinese scientists who traced the H5N1 flu virus's descent warn that it is still evolving, and could give rise to a severe pandemic in humans. They also fear it might now be impossible to eradicate it in east Asia.
The flu reached birds in eight countries in 2004. All the outbreaks were declared over in spring 2004, after millions of birds were slaughtered. But on Tuesday, China confirmed a fresh outbreak of the same flu. It has also re-surfaced in Thailand and Vietnam.
The virus is closely related to the H5N1 flu that was the first bird flu to kill people, in Hong Kong in 1997. The team from Shantou University in Guangdong, China and Hong Kong University report that since 2000, genetically similar viruses have increasingly been infecting chickens as well as their normal hosts, ducks, in southern China.
But since 2002 one family of these viruses, which the team calls genotype Z, has replaced all the others, indicating it possesses a massive selective advantage. Its mutations suggest that this advantage involves greater adaptation to chickens.
The results support earlier suggestions that 2004’s outbreaks originated in China, and resulted from viral evolutionfollowing increased circulation of flu among chickens.
Pigs or humans
The genetic data show the virus is still adapting to its new hosts. This means it will produce new strains. The Z genotype has so far had difficulty infecting humans, but is lethal when it does. If it becomes more adept at this, it could cause a severe human pandemic.
Related research by scientists at the same institutions shows the virus has become steadily better at infecting mammals over the past four years, although whether this is a side effect of its adaptation to chickens or the result of occasional spread to pigs or humans is not known.
The team suggests that the virus might be spread by wild birds. But their research shows that samples of H5N1 flu from wild species form a group genetically distinct from most samples from poultry. There is also no evidence that the Z genotype has taken up stable residence in wild birds.
Journal reference: Nature (vol 430, p 209) |
