Malaria and Thalassemia

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Offline Andy Battaglia

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Malaria and Thalassemia
« on: October 14, 2006, 06:11:58 PM »
This topic was brought up elsewhere but for purposes of organization I will address it in a new topic.

(This post contains quotes from emails I sent to a Roman Catholic sister who was investigating the malaria/thal connection for a course she was taking. In addition to what one can see in this group, there is a lot of work I do privately through emails, etc., and it's nice to get an opportunity to share some of this with the group).

I'd like to clear up a mis-conception about thals and malaria. Thals can and do get malaria. However, malaria does not usually thrive in the blood of thals, resulting in much milder cases that lead to improved immunities against malaria. In fact, it has been found that thals who have had a case of the less severe type of malaria, develop some immune protection against the more serious strain of malaria. There are two types of malaria virus. P. Vivax is the milder form.  Studies showed that young alpha thals were more susceptible to p. vivax but that infection led to a higher resistance to the more deadly P. Falciparum later in life. It seems the only benefit is resistance to malaria and the researchers suggested that the rate of the thal gene would be even higher in the malaria regions if not for the negative effects of thal.  Considering the devastating effects of malaria, the protection given by the thal gene is very significant.

Thalassemia is caused by a mutation in the genes that are responsible for producing hemoglobin in the red blood cells. As is the case with genetic mutations, the actual mechanism that causes the mutation isn't known. Over two hundred different mutations are known to exist in the hemoglobin genes. It has not been shown that malaria causes the defective gene, however it is believed that several genes have been shaped by the struggle against malaria. It is possible that the genes changed to protect against the malaria parasite. The human body has been created so it could adapt to changing conditions, and while this change in just one of the hemoglobin genes offers some protection against malaria, when both are changed it becomes a deadly negative, thalassemia major. While malaria did not directly cause thalassemia, it may have caused the genes to adapt in order for the body to survive. In this case the genes changed to produce red blood cells in which malaria could not thrive .

The parasite that causes malaria does not thrive on the blood of those who carry the thal gene. Why is not understood, but current thinking is that it has something to do with the higher levels of fetal hemoglobin in thal carriers. The malaria parasite does not thrive when high levels of HbF are present. Thals can and do get malaria but most often are not as seriously infected as non-thals, resulting in a higher survival rate for the thals. Studies do suggest that if a thal has one of the milder forms of malaria when young, that it does create better resistance to malaria later in life, but the malaria does not seem to have any immediate effect on the thal condition itself.

I'll give you an example to explain what has been the result of the malaria/thal connection. Suppose there are ten people and one is a thal carrier, and they all get malaria. 10 % of that sample carries the thal gene. Five of them die from the malaria, but the thal is not one of them because the parasite does not affect the thal as much. Now you have five people and one is thal, now making 20% of that population, thal carriers. This is a simple example but it is basically how it has worked. Now, instead of 10 % of the population carrying the gene, 20 % carry it. Because of malaria, the percentage of the population carrying the thal gene increases, because non-thals die at a higher rate from malaria. In the high malaria regions of the world it has worked out so that as much as 30% of the population carries the thal gene.

Thals do get malaria, but generally they tolerate it much better than non-thals and survive at much higher rates. Combined with geographically "closed" societies this has led to the high rates of the thal gene in places like Maldives, Cyprus and Thailand. While large portions of populations have succumbed to malaria, thals have survived and the incidence of the thal gene in the population has become higher as a result.
« Last Edit: October 14, 2006, 06:15:41 PM by Andy »
Andy

All we are saying is give thals a chance.

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Offline SalD

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Re: Malaria and Thalassemia
« Reply #1 on: October 15, 2006, 12:49:31 AM »

Wow!  Nice work Andy!  You do collect a lot of information!

I just wanted to add a little bit in relation to this bit....
Quote
The human body has been created so it could adapt to changing conditions, and while this change in just one of the hemoglobin genes offers some protection against malaria, when both are changed it becomes a deadly negative, thalassemia major. While malaria did not directly cause thalassemia, it may have caused the genes to adapt in order for the body to survive. In this case the genes changed to produce red blood cells in which malaria could not thrive .

I am trying to remember this from the hazy days of uni, so hopefully I will explain this the right way round!  You have described a theory called Lamarckian theory, where the needs from an animal's life can lead to changes in the offspring.  For example, the idea that a giraffe needed to reach higher leaves to eat, and the giraffe had a baby with a longer neck as a result.  Darwin's theory of evolution is slightly different in that it suggests that changes that lead to an advantage are more likely to be passed on.  So, a giraffe might be born with a longer neck due to a random change in the DNA.  This giraffe might be more likely to survive than other giraffes BECAUSE it can reach the higher leaves, thus this change would be passed on and be an advantage to the giraffes who inherit it.  As you state, the chances of someone with a change in their globin genes surviving malaria are higher than those without, and as survivors they are more likely to have children (who are perhaps more likely to survive) and pass the gene on.  It is thought that changes in the DNA arise spontaneously rather than because of need.  So the changes might be a result of a mistake in copying the DNA, and in the case of thalassaemia that change may provide a 'selective advantage'.  Other changes occur that we don't know about because they don't have an effect, or they do not survive.  There is still a lot to be learnt about these mechanisms though.

I hope I am making sense!  It is not that the genes 'adapt' but rather that spontaneous changes occur, some of which prove to be advantageous in certain situations.

Cheerio!
Sal

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Offline jzd24

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Re: Malaria and Thalassemia
« Reply #2 on: October 15, 2006, 05:13:05 AM »
This has been very interesting. I always wondered about the whole malaria thing - thanks for the great info. Jean   :thumbsup

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Offline §ãJ¡Ð ساجد

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Re: Malaria and Thalassemia
« Reply #3 on: October 15, 2006, 05:47:25 AM »
Thanks for the info Andy and Sal.

:yahoo

Now that I have had malaria, I am resistant to it. Amazon jungle, here I come! :biggrin

Take care, Peace!
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Offline SalD

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Re: Malaria and Thalassemia
« Reply #4 on: October 15, 2006, 06:09:06 AM »
 :smile2

Sajid, I don't want to ruin your excitement ... BUT...  :scared there are other nasties in the Amazon apart from malaria....
There are things that might see you and think  :food

But on the other hand... I've been to the Amazon (in Bolivia) and it is a truly amazing place!  I was pleased to make it out without any baddies getting me though!  :wink
Happy travels!!
Sal.

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Offline §ãJ¡Ð ساجد

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Re: Malaria and Thalassemia
« Reply #5 on: October 15, 2006, 07:14:07 AM »
Hi Sally,

I just said that for fun! I'm not going anywhere soon. You are right about the other things than malaria in the jungle and I want to stay miles away from them :grin

Tell us about your adventure and share any pictures you might have.

Take care, Peace!
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Offline namitha

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Re: Malaria and Thalassemia
« Reply #6 on: October 23, 2006, 08:39:54 AM »
Hi Andy,

Thanx for the info. Wow that was some research! So that's why there is a high percentage of thals in the malaria belts. The whole thing is so ironic. Healthy people die of malaria and thals with a 101 problems survive! Weird Nature. Sorry I feel this way but Thal is a lot nastier than malaria. Atleast malaria has a cure, but thal has none  :hissyfit

Regards,
Namitha
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no less than the trees and the stars;
you have a right to be here.

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Re: Malaria and Thalassemia
« Reply #7 on: October 24, 2006, 04:41:24 PM »
That cleared up a few of my questions, many of the websites that I have been looking at, basically made me think that Thals can not get malaria... thanks Andy for clearing that up.

 

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