Deadly flu evades body's defences
Virus treats the immune system like
"duck soup".
26 August 2002
JOHN WHITFIELD
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| Influenza can be a fatal
infection. |
| © GettyImages |
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The lethal Hong Kong influenza is invisible to our body's
immune defences, new research shows. The finding could help to
identify future dangerous 'flu strains and perhaps explain why
'flu outbreaks of the past were so deadly1.
The strain in question, called H5N1, is immune to molecules
called cytokines - the first line of defence against 'flu.
In 1997, H5N1 jumped from chickens to humans in Hong Kong.
Eighteen people were hospitalized, six of whom died. Three
million chickens were slaughtered to contain the virus, which
can spread from birds to humans, but not between people.
"After infection with 'flu, cells start churning out
cytokines," says virologist Robert Webster of St Jude Children's
Research Hospital in Memphis, Tennessee. This triggers an immune
response in uninfected cells, and suppresses most strains.
But to Hong Kong 'flu, cytokines "might as well be duck
soup", says Webster - "it totally ignores them".
Simple but deadly
Just one genetic mutation lets H5N1 evade cytokines,
Webster's team found. The researchers put the crucial gene into
another form of 'flu; infected pigs became much sicker than
those given the unmodified virus. The animals also remained
infectious for longer.
Now the gene has been identified, it could be used to track
down other threatening 'flu strains, says Albert Osterhaus, who
studies 'flu at Erasmus University in Rotterdam, the
Netherlands.
Quite how H5N1 sidesteps the immune system escape is not
known. It may have other nasty tricks besides the changed gene,
says Osterhaus. The effects of 'flu depend on the way that its
eight genes interact, and that differs depending on the species
it infects.
Back with a vengeance?
Hong Kong 'flu is similar to the strain that killed more than
20 million people in the 1918 'flu pandemic, Webster says. Both,
for example, killed people in their mid-30s, who should have
robust immune systems. They might share the immune-dodging
ability, he thinks.
But there are also differences between the strains, says Alan
Hay, a 'flu researcher at the National Institute for Medical
Research in London. "It's a novel and very interesting finding,"
he says, but "it doesn't tell us anything" about the 1918
pandemic.
Influenza has been touted as a bioweapon, and the news about
H5N1 could be used to produce a more deadly strain. It's always
a possibility, says Webster, but 'flu is not the most obvious or
easiest candidate for malicious use.
The threat we already face from the disease means that the
benefits of the research outweigh the risk of new knowledge,
Webster says. "We have to have this information. Sooner or later
we're going to get a bad one, and by understanding the beast
we've got a better chance of killing it." |
