[Brian Roe]

Brian Roe asked the Naked Scientists:

I believe I am correct when I say that viruses keep evolving.  If this is true, will there come a time when the virus gets away from us where we will not be able to stop it?  Or will we eventually catch up to it to rid it or at least
control it?

What do you think?

[mario]

Human viruses won't out evolve us- they need us as hosts, they need us to proliferate. And evolution is not directional, it is random. The rate of evolution depends on the number of selection pressures being applied on an organism.  I doubt a single virus would ever wipe us out, as it is highly likely that there would be a group of people who possess a mutation protecting them against a particularly strain of a disease. I guess viruses/bacteria etc keep evolving at a rate proportional to the selection pressure we keep applying (ie. Antibiotics/ anti-virals). It’s a double edged sword really, any treatment we come up with will eventually become obsolete as the disease inevitably becomes resistant.

[rosalind dna]

That is how the MRSA bug started because of over-usage of anti-biotics and the same for the bird flu H5N1.

Which could be similar to the spanish flu that killed more people after WW1 than the actual war did.

SARS was an airborne virus I think.

[chris]

Good answer Mario, but I think Brian's thinking more in terms of viruses gaining the ability to outrun our immune system's ability to respond to them...like HIV for example.

Chris

[mario]

hi chris, I guess in HIV's case it does outrun our immune system, but over many years giving it time to infect other people.

In evolutionary terms, i would have thought it would be disadvantageous for a virus to instantaneously overcome our immune system, as it would kill its host before it has a chance to infect other people. A think a virus reaches a sort of equilibrium regarding its virulence and its affect on our immune system. Reaching an optimal point where it can replicate and be transmitted to another person.

[chris]

Yes, that's right. Viruses tend to fall into several camps: "smash and grab" types, like smallpox or measles, which infect once and either kill you or render you immune, and "doppleganger" types, that change rapidly so that they constantly appear different to the immune system, enabling them to circulate continuously in the population, often infecting the same individual many times, like flu. Then there are the "silent, indolent but deadly" types, like HIV, which slowly and steadily dismantle the immune system, but leave the infectee healthy in the interim, but also infectious; this allows the virus to spread to multiple other people before the host dies.

Taken to its logical conclusion, viruses like HIV would eventually become chronic rather than fatal diseases, if evolution was left to its own devices. In essence, strains of the virus would be naturally selected that left hosts infectious but healthy for the longest time, since this would translate into the maximum number of transmissions. At the same time genes from the host population would be selected that rendered cases better able to resist or co-exist with the virus, minimising host harm.

This is was have happened in the monkey world with SIV, the immediate ancestor of HIV.

Chris