Bird flu viruses
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When pigs fly

Is this a chance for pigs to fly? If you don't know what I'm talking about - and if you're not a virologist or public health specialist, you could be forgiven for not being too worried about pigs with bird flu - let me explain.

A researcher from the Harbin Veterinary Research Institute gave a paper at an international symposium on Sars in Beijing recently detailing an alarming finding. According to a table presented with the paper, pigs from farms in parts of China had been infected with H5N1, avian influenza. This information set off a storm in the infectious-diseases world.

Plenty of humans have been infected with bird flu, but there are two reasons for wanting to know when and where pigs contract it. First, according to research into the great flu pandemics (including the Hong Kong flu of the late 60s), pigs top the list of suspect causes, because they're similar to humans in many ways. One similarity is in the receptors of cells lining their throats and lungs that can provide a gateway for the flu virus.

This means pigs can catch human-flu viruses, as well as avian varieties. Now, if two influenza viruses set up home in the same cell, they might mate. And if the right genes mix, we might end up with a new superflu.

Pigs could breed an influenza virus that's not only able to infect humans by getting onto their hands or into their mouths, but one that could jump from human to human via coughing. This hasn't happened yet, but every time a new human case is reported, samples are carefully analysed to prove it's H5N1 and to see if any genetic mixing has been going on.

The second reason for the anxiety generated by the report is that, although it's hard enough to monitor humans and to analyse the viruses infecting them, it's a logistical nightmare to keep watch on pigs all over China (not to mention the rest of Asia). Regular checks are made on pigs in Hong Kong and Vietnam. So far, none has been found to have avian influenza.

So, experts are worried when a report like this turns up out of the blue - almost as an aside at a conference on Sars - highlighting that no-one told the World Health Organisation that the pigs have been growing the virus. It looks a bit like the same old problem that let the Sars outbreak get out of hand: officials sitting on crucial information.

What can we do about all this? For one thing, anyone with influence in the mainland should try to persuade the authorities not to revert to the bad, old ways, but to share medical information with those most able to help: the world's virologists, WHO's public-health specialists and the networks they've set up. Our own government needs to be active in asking for more information and offering to help work on this kind of material, because we have a wealth of expertise and experience.

At an individual level: don't forget the personal-health and hygiene guidelines we learned during Sars.