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Monday, January 09, 2006

Why Turkish Human Bird Flu Cases Are Important

Reading the western press makes me believe that most people aren't getting it, so I will take the beginning post from this FluClinic Discussion thread as an opportunity to explain why the events in Turkey are important to you:
It seems a little strange to me that most people on this forum are sooo scared of this H5N1 virus. I have read up on it and it is scary....for birds. but come on...it has only infected around 70 people. The possibility of it transforming so it can pass easily between humans is pretty slim. It has had chances to make that mutation for years already and it hasn't...why would it now?. I am pretty much 100% sure that a year from now we will be in the same situation as we are now, more birds getting infected, and once in awhile an unlucky person will get H5N1 from a bird. Please don't flame me because this is "flu discussion" so people should be open to the possibility that a pandemic will never occur. I doubt one will occur in my lifetime and I am 21. We have come so far with prevention and vaccines for this sort of thing. If for some bizarre reason this virus did take on this mutation (which would be the odds of like 1 in a million imho) countries would be able to defeat it and there wouldn't be much commotion because we would stop it before it even got a chance to really take off. We should really have more faith in our governments to deal with this. They are working around the clock in preparation for any sort of natural disaster. We can all sleep better knowing this, and we don't have to worry everytime we hear about someone getting infected with the bird flu imho.
Taking his points in order:
1. It has only infected around 70 people....
Wrong. The official WHO count is 146 and rising, with four of those coming from Turkey, and over half of them fatal. However this is a big undercount. Take, for example, the fact that the two most populous countries in the world (containing about a third of the world's total population), India and China, have not been reporting cases. China has just begun to report, but unofficial reports have suggested that they have had hundreds of cases.

Also there are diagnostic problems because the virus is not well adapted to humans yet, so throat swab and nose swab tests are often false negatives. A disturbing number of cases are confirmed only on autopsy, but PCR testing shows more infections. There have been no sero-prevalence studies, so we don't know the real incidence of mild cases. It is likely that Turkey will show far more mild cases based on PCR/antibody testing with many less deaths and cases of serious illness. In any case, it appears that at least 40 people in Turkey will be confirmed, which is a huge expansion of the world total in about one month, and demonstrates the degree of underreporting.

2. The possibility of it transforming so it can pass easily between humans is pretty slim.
At this time the possibility cannot be quantified. However, it is well documented that the Qinghai strain has acquired some genetic code that make it easier for the virus to breed in humans, and observation of the Qinghai strain has shown that it is spreading rapidly outside Asia. So we know the virus is mutating rapidly.

Specific known mutations it has acquired are PB2 E627K which is associated with virulence in mammals (it is believed to assist propagation at lower body temperatures) and the acquisition of multiple sequences at the cleavage site for HA. The reason why those multiple sequences are so important is that they allow the virus to replicate more efficiently.

Here's why. This type of virus invades the cell in the host and uses the chemical machinery in the host to make copies of itself. Eventually the cell explodes and the copies invade the bloodstream seeking other cells to invade. But the replication process is inefficient with many errors, so most of those copies are not viable and cannot replicate. But when the cleavage site acquires a string of possible connectors, many more flawed copies are still viable - so the virus becomes capable of reproducing inside the body far more quickly.

Finally, although the risk of developing a human to human strain is unknown, research published in 2005 showed that the 1918 pandemic seems to have been a virus that jumped directly from avians into humans without the necessity of reassortment. This implies that whatever the risk is, it is far higher than scientist thought it was a year ago. Couple that with the evidence of increasing human disease, and it is clear that opportunities for acquiring genetic code making the virus more efficient at infecting humans are rapidly increasing.

3. It has had chances to make that mutation for years already and it hasn't...why would it now? I am pretty much 100% sure that a year from now we will be in the same situation as we are now, more birds getting infected, and once in awhile an unlucky person will get H5N1 from a bird.
Because of the factors listed above, we know that the virus is mutating, so the process is already under way. The virus has begun to cause more human disease over the last couple of years and now it is increasing its geographic range. The "unlucky persons" are becoming more frequent and this is happening over a much larger area. With each infection of a human being, the chance for the virus to acquire additional genetic code which makes it more efficient at infecting humans increases. Again, whatever the unknown risk is, it is clear that the risk is increasing. We are not in a steady-state situation.

4. We have come so far with prevention and vaccines for this sort of thing. If for some bizarre reason this virus did take on this mutation (which would be the odds of like 1 in a million imho) countries would be able to defeat it and there wouldn't be much commotion because we would stop it before it even got a chance to really take off.
This is completely untrue. Currently the world production of flu vaccine is about 300-400 million doses per year, and it takes about a year to make those doses. The tests of the vaccines that have so far been developed have shown that much higher than normal doses were required to confer substantial protection against the older strain of the virus, so halve that to 150 million doses. However most authorities doubt that the vaccine already developed would confer much immunity to a pandemic strain anyway. The current world population is over 6 billion. We cannot develop an effective vaccine against a strain of virus which doesn't yet exist, and even if we could we don't have the capability to produce enough vaccine to vaccinate one twentieth of the world population within a year. This is why the governments are so concerned. The best we can hope for is to combine antivirals and a vaccine that might provide some possible resistance in order to keep essential services running should a pandemic occur. In other words, we have to keep the doctors, nurses, EMT's, police, truckers, etc on their feet. But it seems unlikely that we will be able to do even this.

5. We should really have more faith in our governments to deal with this. They are working around the clock in preparation for any sort of natural disaster. We can all sleep better knowing this, and we don't have to worry everytime we hear about someone getting infected with the bird flu imho.
It is not that the governments of the world wouldn't do whatever they could, but for the reasons listed above there is little that they can do. This is why the US government has begun advising citizens and businesses to prepare for serious disruptions of economic life. They have analyzed the situation and do not see that they have any ability to prevent a pandemic.


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