In laboratories around the world, scientists are readying for the fight against bird flu, and the threat of a global pandemic. Amanda Dunn reports.
Influenza is one of science's slippery customers. It is highly unpredictable, has the ability to mutate - meaning any vaccine has to be updated regularly - and causes epidemics every year, usually during the winter months.
It can also jump species and, if conditions are right, do what health authorities now fear the bird flu ripping through Asia might do - make its way into a person who also has a human flu, and mix genetically to produce a new, highly transmissible strain that will cause many people to die before a vaccine can be made widely available. But the experts cannot say how likely this is to happen. The consensus seems to be that the risk remains low, but the simultaneous outbreak of bird flu in so many countries is unprecedented, and the more of the virus there is, the greater the chance of it changing into a deadly human strain.
The strain that is causing most of the disease, H5N1, is highly pathogenic and has already shown its ability to jump species, causing at least eight human deaths in this outbreak.
History shows just how grim a possibility a new, virulent flu strain is, with influenza pandemics traditionally occurring about three times a century - the last being the Hong Kong flu that struck in 1968, causing a high number of deaths.
According to Graeme Laver, influenza expert and co-inventor of the anti-viral drug Relenza, the current situation is "an enormous threat, an enormous concern". He paints a grim picture of how dire the consequences might be if bird flu becomes a human virus, and believes it would be the worst flu pandemic the world has seen since the Spanish flu of 1918-19, which claimed between 30 and 50 million lives.
Others are more cautious. Ian Gust, a Melbourne University professor of virology and World Health Organisation expert on influenza, says the odds still favour such a disaster being averted. There is no question, he says, that it is a very serious outbreak of avian influenza - with a very high death rate in bird populations - but the virus is believed to have been around for several months, and does not appear to be highly infectious to humans.
But what of the worst case scenario? At what point would the experts know they had a pandemic on their hands, and what could they do about it?
The first indication of trouble, Professor Gust says, would be more people turning up to hospitals in a particular region with influenza that could be traced back to an association with infected birds. The patients would have severe respiratory symptoms, and the death rate could be high.
If the disease was confirmed as a virulent hybrid virus, WHO would crank up its pandemic plan, issuing various levels of alert for national health bodies around the world to implement. Vaccine manufacturers would also swing into production - providing they had an appropriate strain with which to work.
The key centres dealing with bird flu strains - the National Institute of Biological Standards and Control in London, and WHO's Collaborating Centre for Avian Influenza in Memphis, Tennessee - are working on a prototype strain for H5N1 taken from a recent victim of the virus.
A bird flu strain was made available based on last year's model but, explains Alan Hampson, deputy director of WHO's Collaborating Centre for Influenza in Melbourne, the virus has mutated in the meantime, meaning "the match is not all that good antigenically".
The extra complication where bird flu is involved, Professor Gust says, is that the virus cannot be grown in eggs, as is usual practice in making vaccines, because it would simply kill the eggs. Instead it has to be put through a process known as reverse genetics technology to engineer a strain that both grows in eggs and protects against the bird virus.
Even if the manufacturers were ready to go when a human-to-human virus appeared, it would still take at least six months for a vaccine to be widely available. And in that time, the virus would be likely to have made its way very quickly around the world and caused many deaths.
In the gap between outbreak and vaccine, says Professor Laver, the only hope is the anti-viral drugs Relenza - in which he maintains a financial interest - and Tamiflu. Another, older class of drugs, M2 inhibitors, have been used to treat influenza, but WHO says initial analysis suggests the H5N1 strain is resistant to them.
But a professor of virology at RMIT University, Greg Tannock, says the supply of anti-viral drugs would be a problem. "We're never going to get it out to everyone," he says. "There's not enough of it around."
So now, a furious slaughter of millions of chickens in Asia - with some countries also vaccinating birds - is trying to wipe out the avian influenza, and stop it from jumping to humans. Testing and diagnosis of virus samples from the region is also under way to ascertain which strain is causing bird flu in particular areas. In high-security labs at the CSIRO Australian Animal Health Laboratory in Geelong, scientists are fine-tuning diagnostic tests for bird flu in animals, and diagnosing samples sent to them.
Laboratory director Martyn Jeggo says the mass slaughter of birds is distressing and difficult for farmers, but the only effective way to bring the virus under control. Dr Jeggo believes there is little threat of birds bringing the virus to Australia, given our stringent quarantine laws, and that bird migration is now heading from our shores.
As for the human threat, the behaviour of the virus defies prediction. If transforming into a human-to-human virus is one, albeit slim, possibility, the other is that, through the culling of birds, the virus will run out of hosts and play itself out. "With the flu," Professor Tannock says, "expect the unpredictable."
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