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Watch out for the other bird flu
22 September 2008
From New Scientist Print Edition.
Debora Mackenzie, Oxford

Whatever happened to bird flu? The H5N1 virus has been storming across Eurasia and Africa since 2004, destroying birds and killing 245 people, according to official figures. But while it has faded from the headlines, governments and scientists are as concerned as ever about the dangers it poses.

In August, the UK government renewed its 2004 assessment that a flu pandemic is still the number one threat facing the country. This week 1200 flu scientists are flocking to a conference in Portugal to discuss the problem.

"H5N1 is still out there killing people," says Rob Webster of St Jude Children's Research Hospital in Memphis, Tennessee. "It's doing what we knew it would do - recombining and evolving."

The biggest fear is that H5N1 will evolve to become readily transmissible between people, and we are starting to learn what mutations it needs to do this. Flu spreads among animals if its H protein binds to sugar molecules on cells lining their throats, and so far H5N1 binds better to sugars more common in birds than in mammals. But Wendy Barclay of Imperial College London, UK, reported at a meeting in Oxford, UK, last week, that just two mutations in the H5 protein are enough to make H5N1 bind to mammalian sugar molecules.

If that happened in the wild, it could trigger a human pandemic. Fortunately, "neither mutation has appeared in any circulating H5N1", Barclay says. This could mean that neither one alone confers a selective advantage for the virus, making it less likely that both will emerge together.

H5N1 is not the only threat. "H9 is the real sleeper, the one we have to watch," Webster says. H9 bird flu can cause mild disease in people, but the H9 virus common in poultry across Eurasia now carries several of the same genes which make H5N1 so deadly; a few more mutations and H9 could become a killer too. Many of these poultry have also been vaccinated against H9, which is worrying, because H5N1 probably evolved into a killer in H5-vaccinated poultry, raising fears that the same thing could happen with H9.

Another threat is H2. No one born since 1968, when H2 disappeared as a human flu, is immune to this strain. A deadly H2 appeared in pigs in 2006, but was quashed. "We dodged a bullet," says Webster.

The good news is that 72 prospective H5N1 vaccines are now being tested in people, and genetically modified viruses that can be grown to produce flu vaccine for H9, H2 and others are being created.

The bad news is that one strain of ordinary human flu, H1N1, has spontaneously developed worrying levels of resistance to the antiviral drug Tamiflu. This calls into question the strategy, which many countries have adopted, of deploying Tamiflu as the first line of defence against a pandemic. It has also mystified virologists, as it shows that drug resistance evolves readily in flu, and does not weaken the virus as some believed it would.

Meanwhile, the European Union is launching a study of a defence strategy called social distancing, which involves measures such as quarantine, school closures and the like. An analysis of data from the 1918 pandemic by historian Howard Markel of the University of Michigan, Ann Arbor, suggests that in some US cities such measures halved the death toll.

From issue 2674 of New Scientist magazine, 22 September 2008, page 8

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