I'm not one for complacency concerning the next great plague, but surely the virus that caused the most devestating pandemic of the last century is a far more direct threat than a virus that has so far only killed sixty-four people worldwide, so recreating the one to understand the other seems a bit heavy-handed.

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The 1918 virus actually had a "small" death rate (I think around 5% of those infected died) while the current H5N1 virus' death rate may be higher. We currently have no immunity to H5N1 while in general the population does have some level of immunity to the 1918 virus, since the people it didn't kill went on to have children and passed on whatever genetic resistance we had to the virus. It is also possible, though I haven't looked it up, that less-nasty variants of the 1918 virus have been cirulating in the population ever since, thus allowing people to build up immunity to it.

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H5N1 has been extremely lethal to poultry with an incredibly high death rate on the order of 90%. That combined with the 30-50% fatality rate among known human cases has the experts quite concerned. Estimates for a pandemic are that the death rate could be as high as the 1918 H1N1 strain but no one expects it to be 30-50%.

You have to consider the death rate along with the case rate for it to have any meaning. Small Pox kills 30%, rabies kills almost 100%, and so on but it also matters how many people get infected. Mice were infected with the 1918 strain that was reconstructed and they turned out to shed very large numbers of virus. That likely contributed to the number of fatalities as much as the death rate.

There are some that are very unhappy not just that the 1918 virus was resurrected but that the genetic information was then made public and readily available. One can only hope other researchers will not be careless when they decide to repeat the research.

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I think what hasn't been stated is that the main reason that the current virus has only killed 64 people is that so far it has not mutated to be able to be transmitted directly from human to human.

If it can manage to mutate so that it can, combined with the high death rate as pointed out by others in this thread, then the overall threat is very great indeed.

And from what I have read, the virus is mutating fairly rapidly, so it is not an idle worry that it will be able to eventually move from human to human.

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My question is, which is more likely, that a particularly nasty virus that so far does not spread from human to human will mutate to obtain that ability, or that one of the many viruses that already can spread from human to human will mutate to become particularly nasty? Does anyone know this? And if not, then why is this new threat getting so much press?
Furthermore, we already have a particularly nasty virus that does spread from human to human, under the right circumstances. It is called HIV, the scourge of many undeveloped areas. Why is the potential threat of H5N1 worth more air time than the known threat of HIV? Oh yeah, I forgot-- the news cycle.

The viri that already pass human to human are simiar to existing viri and our bodies are better able to cope with it. It is easier to make up vaccines for this too.

Flu viri mutate easily and readily. It is likely that the thing will eventually jump to humans, most likely through a third animal. And when it does we will have zero immunity to it. So if it comes it is likely to be very dangerous, while existing human flu viri will mutate but are not likely to instantly become so different from existing lines as to be nearly as lethal.

Researching HIV is not mutually exclusive of researching the flu. HIV is not new, and so it does not garner a lot of face time on TV or the front page. It also is not likely to wipe out a continent worth of people inside of a month once set loose. This new flu thing is news because it is something changing in our lives and our environment. I am not putting one as more important than the other, but the flu can kill large numbers in a short time and can spread in a day or two to every corner of the earth.

Another factor is political. There is a segment of society that still looks upon HIV as somehow dirty or sinful. They think that all HIV victims are promiscuous drug users. They fight efforts to send substantial aid. There is no social stigma attached to the flu. Furthermore, flu can come and take down my family, while the likelihood of my wife and I contracting HIV is vanishingly small. The flu thus threatens my family while HIV does not. Not directly anyway.

That does seem like a valid point. But where did the avian flu come from? It's new to birds obviously-- by what you're saying, it must have come from something else that was used to it and had immunity to it (or else we have to keep looking for other sources, ad infinitum). I wonder what that was, and if there is already immunity there, perhaps it would help us find a vaccine?

Influenza viruses undergo random mutation all the time as do Corona viruses like SARS and all the other organisms that infect us. Some do mutate more readily, some replicate more abundantly. But a genetic change that make a virus or bacteria capable of causing a pandemic could come from many currently circulating organisms.

HIV emerged when a road was built across Uganda, literally. Truck drivers and prostitutes along the road allowed a virus that had been confined to a small geographic area to break out. From there a variety of just right circumstances allowed the disease to become a world wide pandemic. And it is indeed a major pandemic. Since it kills so slowly, the effect on the world's psyche is quite different than if it were a flu pandemic which kills within days.

The black death (plague) of the middle ages became a pandemic when rats on ships brought it to cities that were crowded and infested with rats and fleas. Tuberculosis became a pandemic when rural dwellers moved into crowded cities.

Sometimes it is the organism that changes, sometimes it is other circumstances that allow a disease to spread. Rheumatic fever from strep throat infections, rapidly invasive group A strep, meningococcal disease, and many other bacteria can go from mild or no disease to rapidly fatal by just having small genetic variations. Corona viruses can cause a mild cold or fatal SARS with very small genetic differences.

Just about any infectious organisms can mutate into a deadly version by mere chance. After that, milder versions tend to be selected for as the worst cases tend to kill the host before spreading.

The reason everyone is so worried about a pandemic of influenza is because they have occurred on a regular basis in the past. In addition, the influenza pandemics of the past have been preceded by the development of a substantially new virus in birds. It's like earthquakes, we know they will happen we just don't know when.

There are some researchers who think H5 viruses will never become highly contagious in humans. On the other hand, this particular strain is following the pattern of past pandemics. What is really happening is we know a lot about human flu pandemics but we don't know quite enough to know if this is the beginning of one or not.

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Flu viruses circulate in birds just as they do in humans and many other species. Every so often chance mutation allows the virus to invade more readily, make mores copies, make a deadly enzyme or any number of other changes that cause a higher fatality rate. In the case of flu viruses, not only do they mutate, but they also reassort their genes with other flu strains leading to new combinations just like human offspring are a mix of the parents. This makes new strains particularly common with this virus family.

We have a vaccine. The problem is making enough of it fast enough. And the second problem is adjusting the vaccine in time when the virus shifts genetically to become contagious among humans. We can't predict those changes ahead of time and we can't make vaccine in less than a few months.

In 1918 the flu virus spread worldwide in 4 months without air travel. It not only takes that long to make vaccine, the vaccine manufacturers met 2 years ago in Europe and predicted if all the capacity to make vaccine was used, in 6 months they could make enough for 5% of the world's population.

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Not necessarily easier to make vaccine, but the current H5N1 vaccine is taking larger amounts and 2 doses to confer immunity because humans don't have preexisting immunity to similar strains.

This is the current theory but the resurrection of the 1918 flu strain indicated it may have not reassorted in pigs but rather mutated directly to become infectious in humans.

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Thanks beskeptical, it sounds like you have a great deal of knowledge about this and are good at communicating it clearly. The thing I still don't understand is, if a virus that already existed in birds but wasn't so deadly can mutate to one that is deadly for birds, then why do human pandemics have to start with birds? If a bird pandemic can appear in birds all by themselves, why would it not be easier to get human pandemics from humans all by themselves?

Human pandemics can begin in humans. HIV is one such pandemic. Though the virus spread from other primates to humans a few 1,000 years ago, it was the change in circumstance that led to the current pandemic.

But there are reasons pandemics begin in other species. When a disease is particularly deadly, it kills the host too fast for the infection to spread. So milder disease is often selected for genetically since it spreads more easily. That makes deadly pandemics less likely to emerge in the species being killed.

In the case of bird flu, though domestic birds are dying at very high rates, many wild birds with the same infection are not, and neither are pigs which is also a problem. The virus then has the opportunity to evolve into something that spreads among one species while becoming very lethal to another. When events occur that allow the virus to jump to another species, the lethality can be very high. After the pandemic runs its course, milder organisms are selected which don't kill the host.

In other words, the mechanisms of natural selection have given us the recurring deadly bird flu pandemics. It just so happens human and bird genetics are a set up for this particular virus to evolve in birds and occasionally jump to humans. Domestic birds are a big part of the equation since close human bird contact occurs there.

By the way, we also get bird flu virus infections that are not deadly. They are now referred to as low pathogenic avian influenza viruses, LPAI. The current H5N1 is considered a high pathogenic avian influenza virus, HPAI.

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I see, I had forgotten that.
Thank you, this is very insightful. A lot of things are making more sense. Also, I reach two conclusions based on what you said. Can you confirm:
1) there should be a maximum-threat kill percentage, perhaps near the 5% (?) of the 1918 virus (too high and the virus can't spread quickly enough to cause a pandemic, too low and it won't lead to that many deaths).
2) the people who die from a virus are less of a threat to the overall population than those with immunity, as the latter are more responsible for its spread. Not that I mean to imply any culpability or blame, we all spread viruses and it's not anyone's fault unless done intentionally.

Also, I wonder if the issue with birds might go beyond the genetic relationships to humans, to include the simple fact that birds fly? Since people fly now, a lot more than in 1918 (thuogh not as much as birds of course), maybe birds are not as crucial a component of the equation going forward?

Hey, I fly more than a bird.

Always providing, of course, that said bird is either a penguin or an ostrich.

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Well there are many factors involved so one cannot look at a single factor in isolation. HIV is close to 100% fatal and look how far it is spreading.

Again, it depends on period of communicability, rate of viral shedding, number of contacts with susceptible persons and so on. With SARS there were certain individuals that shed a lot more virus than others. Whether or not they lived or died may not have had much affect on the number of persons they infected.

Once a flu pandemic begins in humans, birds no longer play a role. And the fact we have air travel now will definitely have an impact should we get a virus similar to 1918 influenza.

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Oh I see, the mutation that allows it to go person-to-person would happen in a person, not in a bird, correct? Could you imagine countries closing their borders if the virus started going person to person somewhere?

I just hope the next time a pandemic occurs, that we do not blindly attribute the cause without due diligence. Large areas of medical science still borders on the unknown. And one man's retrovirus is another man's mycobacteria.

http://www.sumeria.net/aids/001PDF~1.PDF

Yes. Even if they didn't, people will voluntarily reduce travel (remember SARS?)

Within a country, there may be specific limits on some kinds of travel. Individuals who have been exposed would be asked to voluntarily confine themselves to their home.

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