Why were colds so bad for indigenous inhabitants?

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Andrew Douch

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Andrew Douch  asked the Naked Scientists:
I love the show... my kids and I listen to it when we are in the car. It always gets us talking about interesting things.

I have a question.

When caucasians colonised Australia, many indigenous Australians died because of the common cold and influenza viruses which they had not been exposed to previously. But surely the immune systems of indigenous Australians would work in the same way as those of caucasians. Yet when we get the flu or a cold, we don't die from it (usually) - because our B and T cells can respond and make antibodies etc to fight it off.

So why did that not happen in those Australian populations?

Does having had exposure to a virus with SIMILAR antigens somehow help the immune cells more quickly identify and respond to a new (but somewhat similar) set of foreign antigens? It almost seems like exposure to (say) a flu virus - leads the B and T cells to make versions of themselves that are slightly different in case an altered form of the antigen should enter again. Do you see what I am asking? It's almost like we are partially immune to a new strain of the influenza virus????

What do you think?



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Why were colds so bad for indigenous inhabitants?
« Reply #1 on: 02/05/2008 10:30:33 »
There are three factors as I see it:

1) As Andrew suggests, exposure to related diseases does confer some cross protection.  An example of this was the use of the cowpox virus to confer protection against smallpox.

2) A disease caught in childhood may be very different from the same disease caught in adulthood (before the use of cowpox to vaccinate children against smallpox, there was a time that very young children were inoculated using live smallpox virus.  This was dangerous, and children died, but their risks were less than if the caught the disease later in life, so it was seen as a valid trade-off).

3) Lastly, maybe not often talked about, and maybe not very politically correct to talk about it, but there is the effect of evolution.  If a population is exposed to a disease over many generations, then those families which are most susceptible to the disease will be killed off by the disease, and the remaining families will have a better natural resistance to the disease.  If a population has never been exposed to the disease then there will be many families within that population that will be particularly susceptible to that disease.

An example of this is that in areas where malaria is prevalent there is a rise in the number of families that carry the gene for sickle cell anaemia and for thalassemia, because these genes confer some protection against malaria; but in areas where malaria is uncommon, the cost of carrying these genes outweighs their advantages.


Offline iko

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Why were colds so bad for indigenous inhabitants?
« Reply #2 on: 02/05/2008 23:14:24 »
Indeed, George

...and there is more evidence for natural selection in malaria.

Malaria selective 'push' went further, and the very 'handle' on human red cells, the surface antigen called Duffy, somewhere has been lost over the centuries, to counteract parasite infestation:

At the red cell membrane, the Duffy antigen is the molecule used by the parasite P. vivax to enter the red cell. The high association of Duffy antigen null rell cells in some groups of people with sickle cell trait suggested that the Duffy antigen might provide some protection against malaria (Gelpi and King, 1976). Later investigations showed the Duffy antigen to be the receptor by which the merozoites of P. vivax enter red cells. People who lack the Duffy antigen (FY*O allele) are resistant to P. vivax (Hamblin and Di Rienzo, 2000). The Duffy null phenotype is most common in people whose ancestors derive from regions in Africa where vivax malaria is endemic.

« Last Edit: 02/05/2008 23:30:52 by iko »