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Instant Expert: Bird Flu
The H5N1 strain of influenza - often referred to as bird flu - is first known to have jumped from chickens to humans
in 1997. Since 2004 it has ripped through poultry and wild bird populations across Eurasia, and had a 53% mortality rate in the first 147 people it is known to have infected. Health authorities fear this strain, or its descendent, could cause a lethal new flu pandemic in people with the potential to kill billions.
Flu has been a regular scourge of humanity for thousands of years. Flu viruses each possess a mere 10 genes encoded in RNA. All of the 16 known genetic subgroups originate in water birds, and especially in ducks. The virus is well adapted to their immune systems, and does not usually make them sick. This leaves the animals free to move around and spread the virus - just what it needs to persist.
But sometimes a bird flu virus jumps to an animal whose immune system it is not adapted to. In chickens - originally a forest bird and not a natural host - it causes a moderate disease but can readily mutate to a more severe, highly pathogenic strain. Just such a strain of H5N1 flu, named after its surface proteins, began rampaging through large chicken farms in east Asia sometime before 2003.
That was of concern because, in 1997, scientists found for the first time that H5 flu could infect humans. It was found in 18 people, six of whom died. All the poultry in Hong Kong were destroyed to stop the threat. But it continued to circulate, especially in China.
There were further human cases in China in 2003. Then in early 2004 Vietnam reported widespread poultry outbreaks and some human cases. After initial denials, Cambodia and Thailand admitted they had outbreaks too, followed by Indonesia, then China. That was immediately after China had denied a New Scientist report that scientists strongly suspected Chinese outbreaks.
The infection also reached Japan, Malaysia and South Korea, but mass culling stopped it spreading there. But outbreaks continued in China, Indonesia and Vietnam, where the virus persisted, most probably in ducks. In 2005, China and Indonesia reported their first human cases.
European invasion
In summer 2005 the virus swept across birds in Russia and Kazakhstan, reaching the Ukraine by January 2006. However, there were no reported human c ases outside East Asia until December 2005. Then, the virus suddenly appeared in poultry all over Turkey accompanied by the fastest upsurge in human cases yet seen.
But scientists insisted that the virus’s arrival in Europe did not pose a greater threat of a pandemic than its continued spread in Asia.
Attempts to blame the rapid spread of the virus in the Far East on wild birds were discounted early on, so efforts to explain its spread across Eurasia in that way were greeted with suspicion. But in May 2005, thousands of geese died of H5N1 at Qinghai Lake in north-central China. The virus was very similar to isolated samples from southeast China, showing, despite official denials, that it originated there. But it had distinctive differences. This same strain then turned up in H5N1 isolates from poultry and wild birds across Russia, Turkey and Romania, suggesting that this time it probably was being carried by wild birds.
Meanwhile east Asian H5N1 turned up in imported Taiwanese birds in quarantine in Britain. This, combined with a near-miss with infected eagles smuggled into Belgium, led to a European clamp-down on wild bird imports.
The virulent strain could to revert to a relatively harmless wild type in wild birds. However, while it is there, it could be carried to poultry far and wide. It has now reached Africa - where it is feared it could run riot. Wild birds are also implicated in its spread across Europe.
Yet governments resisted repeated UN calls for money to eradicate the poultry infection in poor countries. The World Bank renewed calls for such aid in early 2006, while all afflicted countries struggled to stamp the infection out in poultry, with or without vaccinating animals. The renewed call led to pledges of $1.4 billion - although whether the money will be forthcoming is still unknown.
Making the jump
All this has focused attention on ordinary flu. The three flu families that have jumped to humans in the past mostly cause mild disease. This is because we encounter them, and develop some immunity, at an early age - and also because they have adapted to our immune systems. But it is not totally benign. About 700,000 people die of it each year, mainly the very old, the very young and the infirm.
Flu vaccines for common strains are increasing in popularity, although flu evolves so fast that we need new shots every year. In 2004 an unexpected shortage of vaccine in the US underscored the fragility of the vaccine supply, which is produced by very few manufacturers.
But flu is at its most deadly when it first jumps to people, having had no opportunity to adapt itself to our immune s ystems. H5N1 has continued to infect humans as the outbreak in poultry has raged, with an apparently high fatality rate. It has so far been hard to contract, and has not spread readily between people. If this viral strain should acquire that a bility, it could become a lethal pandemic.
Deadly pandemic
That is what happened in 1918, when a virulent flu strain appeared in humans and killed at least 50 million people within a few months.
Scientists have managed to reconstruct that virus, showing that it was a bird flu that learned to spread in humans. Ominously, H5N1 is acquiring some of the same adaptations. Some feel that reconstructing the 1918 virus put us at as much risk as H5N1, because of the potential for escape from the lab.
There have been two other pandemics in the past century. The "Asian" flu of 1957 caused between one million and four million deaths, while 1968's "Hong Kong" flu - with about half the estimated deadliness of the Asian flu - caused one million to two million deaths. Both of these were human flu viruses which had recombined with b ird flu viruses, rendering them unrecognisable to the human immune system. The 1957 strain was nearly released by accident in 2005.
Virologists generally agree that we are due for another pandemic. So they are very worried about H5N1, because - like the 1918 virus - it seems to be evolving to become more deadly to mammals. This is largely in China and, possibly, as New Scientist revealed, in vaccinated chickens.
Various countries have now hatched detailed pandemic plans and started stockpiling flu drugs.
Mitigation measures
Fortunately we can make vaccines for the H5N1 strain, although our ability to g et them tested and manufactured in time for a pandemic is in doubt. Once an effective vaccine is produced, yet a nother hurdle would be administering it swiftly.
The only hope of making a vaccine fast enough, once a pandemic starts, is with low doses of the virus - as the world has limited capacity for growing vaccine virus. But the first tests of a vaccine against H5N1 showed, as New Scientist predicted, that very high doses were needed for vaccine formulated in the same way as ordinary flu vaccines. More disappointingly, later tests showed even vaccines using an immune-stimulating adjuvant require high doses to work. Various trials of vaccines are underway around the world, but they were slow to get started.
The only backup in the absence of vaccines is antiviral drugs. A few new ones are on the horizon, and there are signs that other classes of drugs, used now for blood pressure and cholesterol, may have surprising abilities to stave off serious complications of flu.
But existing antiviral drugs are in short supply. In a successful test of world trade regulations governing patented drugs, several generics manufacturers are now making Tamiflu, the main antiviral, although it is n ot clear whether H5N1 resistance to the drug will be a problem or not.
In June 2005, New Scientist reported that the H5N1 in East Asia was already resistant to the other major class of antivirals, the adamantanes, because Chinese farmers had fed them to poultry.
The H5N1 virus must change genetically to become pandemic, and it may become less deadly in the process. However, there is no reason to think this will necessarily happen, and a highly contagious virus with a 50% death rate is a terrifying prospect, particularly given the speed of modern international travel. There is also a c hance that it could evolve into a completely new disease, which we could fail to spot before it spreads.
Epidemiologists say that if we spot the first small cluster of cases that heralds a pandemic fast enough, we might be a ble to nip it in the bud by giving everyone in the region antivirals. But there is some question about whether we can move fast enough, and also whether surveillance in east Asia - still home to the majority of human cases - is likely to catch the first cluster in time.
Even if H5 does not trigger the next pandemic, its cousins H7 and H9 could. H7 is present in the same region, and also infected large numbers of Dutch people in an outbreak in 2003. Although it caused few symptoms, and only one death, fears remain that such a poultry virus could cross-breed with a human flu, making it even more dangerous.
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http://www.newscientist.com/article/...-bird-flu.html
Instant Expert: Bird Flu
- 11:31 04 September 2006
- NewScientist.com news service
- Debora Mackenzie
The H5N1 strain of influenza - often referred to as bird flu - is first known to have jumped from chickens to humans
in 1997. Since 2004 it has ripped through poultry and wild bird populations across Eurasia, and had a 53% mortality rate in the first 147 people it is known to have infected. Health authorities fear this strain, or its descendent, could cause a lethal new flu pandemic in people with the potential to kill billions.
Flu has been a regular scourge of humanity for thousands of years. Flu viruses each possess a mere 10 genes encoded in RNA. All of the 16 known genetic subgroups originate in water birds, and especially in ducks. The virus is well adapted to their immune systems, and does not usually make them sick. This leaves the animals free to move around and spread the virus - just what it needs to persist.
But sometimes a bird flu virus jumps to an animal whose immune system it is not adapted to. In chickens - originally a forest bird and not a natural host - it causes a moderate disease but can readily mutate to a more severe, highly pathogenic strain. Just such a strain of H5N1 flu, named after its surface proteins, began rampaging through large chicken farms in east Asia sometime before 2003.
That was of concern because, in 1997, scientists found for the first time that H5 flu could infect humans. It was found in 18 people, six of whom died. All the poultry in Hong Kong were destroyed to stop the threat. But it continued to circulate, especially in China.
There were further human cases in China in 2003. Then in early 2004 Vietnam reported widespread poultry outbreaks and some human cases. After initial denials, Cambodia and Thailand admitted they had outbreaks too, followed by Indonesia, then China. That was immediately after China had denied a New Scientist report that scientists strongly suspected Chinese outbreaks.
The infection also reached Japan, Malaysia and South Korea, but mass culling stopped it spreading there. But outbreaks continued in China, Indonesia and Vietnam, where the virus persisted, most probably in ducks. In 2005, China and Indonesia reported their first human cases.
European invasion
In summer 2005 the virus swept across birds in Russia and Kazakhstan, reaching the Ukraine by January 2006. However, there were no reported human c ases outside East Asia until December 2005. Then, the virus suddenly appeared in poultry all over Turkey accompanied by the fastest upsurge in human cases yet seen.
But scientists insisted that the virus’s arrival in Europe did not pose a greater threat of a pandemic than its continued spread in Asia.
Attempts to blame the rapid spread of the virus in the Far East on wild birds were discounted early on, so efforts to explain its spread across Eurasia in that way were greeted with suspicion. But in May 2005, thousands of geese died of H5N1 at Qinghai Lake in north-central China. The virus was very similar to isolated samples from southeast China, showing, despite official denials, that it originated there. But it had distinctive differences. This same strain then turned up in H5N1 isolates from poultry and wild birds across Russia, Turkey and Romania, suggesting that this time it probably was being carried by wild birds.
Meanwhile east Asian H5N1 turned up in imported Taiwanese birds in quarantine in Britain. This, combined with a near-miss with infected eagles smuggled into Belgium, led to a European clamp-down on wild bird imports.
The virulent strain could to revert to a relatively harmless wild type in wild birds. However, while it is there, it could be carried to poultry far and wide. It has now reached Africa - where it is feared it could run riot. Wild birds are also implicated in its spread across Europe.
Yet governments resisted repeated UN calls for money to eradicate the poultry infection in poor countries. The World Bank renewed calls for such aid in early 2006, while all afflicted countries struggled to stamp the infection out in poultry, with or without vaccinating animals. The renewed call led to pledges of $1.4 billion - although whether the money will be forthcoming is still unknown.
Making the jump
All this has focused attention on ordinary flu. The three flu families that have jumped to humans in the past mostly cause mild disease. This is because we encounter them, and develop some immunity, at an early age - and also because they have adapted to our immune systems. But it is not totally benign. About 700,000 people die of it each year, mainly the very old, the very young and the infirm.
Flu vaccines for common strains are increasing in popularity, although flu evolves so fast that we need new shots every year. In 2004 an unexpected shortage of vaccine in the US underscored the fragility of the vaccine supply, which is produced by very few manufacturers.
But flu is at its most deadly when it first jumps to people, having had no opportunity to adapt itself to our immune s ystems. H5N1 has continued to infect humans as the outbreak in poultry has raged, with an apparently high fatality rate. It has so far been hard to contract, and has not spread readily between people. If this viral strain should acquire that a bility, it could become a lethal pandemic.
Deadly pandemic
That is what happened in 1918, when a virulent flu strain appeared in humans and killed at least 50 million people within a few months.
Scientists have managed to reconstruct that virus, showing that it was a bird flu that learned to spread in humans. Ominously, H5N1 is acquiring some of the same adaptations. Some feel that reconstructing the 1918 virus put us at as much risk as H5N1, because of the potential for escape from the lab.
There have been two other pandemics in the past century. The "Asian" flu of 1957 caused between one million and four million deaths, while 1968's "Hong Kong" flu - with about half the estimated deadliness of the Asian flu - caused one million to two million deaths. Both of these were human flu viruses which had recombined with b ird flu viruses, rendering them unrecognisable to the human immune system. The 1957 strain was nearly released by accident in 2005.
Virologists generally agree that we are due for another pandemic. So they are very worried about H5N1, because - like the 1918 virus - it seems to be evolving to become more deadly to mammals. This is largely in China and, possibly, as New Scientist revealed, in vaccinated chickens.
Various countries have now hatched detailed pandemic plans and started stockpiling flu drugs.
Mitigation measures
Fortunately we can make vaccines for the H5N1 strain, although our ability to g et them tested and manufactured in time for a pandemic is in doubt. Once an effective vaccine is produced, yet a nother hurdle would be administering it swiftly.
The only hope of making a vaccine fast enough, once a pandemic starts, is with low doses of the virus - as the world has limited capacity for growing vaccine virus. But the first tests of a vaccine against H5N1 showed, as New Scientist predicted, that very high doses were needed for vaccine formulated in the same way as ordinary flu vaccines. More disappointingly, later tests showed even vaccines using an immune-stimulating adjuvant require high doses to work. Various trials of vaccines are underway around the world, but they were slow to get started.
The only backup in the absence of vaccines is antiviral drugs. A few new ones are on the horizon, and there are signs that other classes of drugs, used now for blood pressure and cholesterol, may have surprising abilities to stave off serious complications of flu.
But existing antiviral drugs are in short supply. In a successful test of world trade regulations governing patented drugs, several generics manufacturers are now making Tamiflu, the main antiviral, although it is n ot clear whether H5N1 resistance to the drug will be a problem or not.
In June 2005, New Scientist reported that the H5N1 in East Asia was already resistant to the other major class of antivirals, the adamantanes, because Chinese farmers had fed them to poultry.
The H5N1 virus must change genetically to become pandemic, and it may become less deadly in the process. However, there is no reason to think this will necessarily happen, and a highly contagious virus with a 50% death rate is a terrifying prospect, particularly given the speed of modern international travel. There is also a c hance that it could evolve into a completely new disease, which we could fail to spot before it spreads.
Epidemiologists say that if we spot the first small cluster of cases that heralds a pandemic fast enough, we might be a ble to nip it in the bud by giving everyone in the region antivirals. But there is some question about whether we can move fast enough, and also whether surveillance in east Asia - still home to the majority of human cases - is likely to catch the first cluster in time.
Even if H5 does not trigger the next pandemic, its cousins H7 and H9 could. H7 is present in the same region, and also infected large numbers of Dutch people in an outbreak in 2003. Although it caused few symptoms, and only one death, fears remain that such a poultry virus could cross-breed with a human flu, making it even more dangerous.
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