Quote:
Originally Posted by Melissa
Why are scientists having problems curing viruses like the common cold virus and AIDS?
Melissa
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The simple, one-word answer is evolution. For the purposes of this discussion, let's stipulate that viruses are living things (depending upon where you draw the line they either are or are not living). In the last four billion years or so, living things have developed a couple of macro-strategies for ensuring that their genes are passed on. Large, multi-cellular things like us go for the 'be big, complex but at the cost of speed of evolution'. Small, single-cell things like bacteria go for the 'be small, simple and retain the ability to evolve on a dime'. Viruses are even more simple than bacteria.
Pretty much the only way to 'kill' a virus is to give it no place to take hold. This is how scientists scored the one victory we've achieved over a virus--smallpox. To beat that, we simply vaccinated every single person on the planet who *could* be vaccinated. With no place to take hold, the virus died out. It still exists--in freezers in two labs, one in Russia and the other at Ft. Detrick in Maryland.
The problem is that certain viruses evolve REALLY fast. Both HIV and the rhinovirus (a class of viruses responsible for the common cold) are very fast at accumulating changes. Since every copy of every single thing that has lived since that very first replicating gizmo billions of years ago has been *slightly* different than the thing it was copied from, there's a great deal of genetic variation in all living things. What this means is that, for instance, even if we kill off 99% of the HIV viral load in an infected person there will still be 1% that is immune to whatever cocktail of drugs we've thrown at it. (And the reason why, for instance, HIV treatments are a cocktail is *because* without it, we were simply selecting for more robust strains of the virus. This way we're hitting it with too much for it to adapt to at once but that's still not enough to kill it off.) So while we might get rid of almost all the viral load in a body, we can't get rid of 100% of the load and that 1% that has survived will begin replicating, making copies that are almost but not precisely like itself--one consequence being that whatever made it immune to the drug-cocktail will be passe on.
With the common cold all of the same things apply but unlike HIV--where there isn't a reservoir in close proximity--both the influenza and rhinoviruses have non-human reservoirs where they can happily evolve for long periods of time and then, with a mutation, jump over to us. The two most common reservoirs are pigs and birds. In fact that's where all our influenza viruses come from--they are originally pig or bird viruses that have crossed-over. So we have the problem that we saw with HIV but more-so. At least with HIV, there's a way to box the virus in. With flu and the common cold we can't box it in. We'd have to pretty much STOP living in close proximity to ducks, chickens and pigs in order to give it no place to go.
Now, this does not mean that we'll never cure these viruses. I don't think we'll make the advances in nanotechnology in my lifetime but I think in my son's lifetime and almost certainly in my granddaughter's lifetime we will. Imagine, if you will, a very tiny machine about the size of a single bacteria that is inserted into your body at birth. This thing goes through your body, taking a catalogue of your genome, the genome of any commensal bacteria (for example, the Escheria coli in your gut that allows you to digest things) and then saying that anything matching that genome is 'you'. Anything else is 'not you'. (This is, effectively, what your immune system is doing) So whenever something is detected that has a genome that is not 'you', this little gizmo goes about systematically *dismembering it atom by atom*. It literally takes the virus apart.
This is something that I doubt even viruses could evolve fast enough to outwit since it's not really a chemical attack (which is what our drugs do) but taking the thing apart at a much more fundamental level. At present there's no reason why such an application of nanotechnology wouldn't work but that's pure blue-sky thinking right now.
Cheers
Aj