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TWiV 125 Letters

Todd writes:

Hey Docs!

I'm a computer programmer who listens to podcasts on my long commute. The highest science education that I've had was college Chemistry. As an Electrical Engineer the science classes we took tended to not be biology oriented, so while some of it is over my head, to say that I find biotech and molecular biology fascinating is an understatement.

Virus related question: I also have a picture of me with the mumps at around 4 years old (1974). When did the MMR come out? Was I one of the last in my generation to have it? I've never met anybody my age who's had the mumps, only older than me.

P.S. Lately I've been listening to the FiB, TWiV, and TWiP podcasts to the point where I'm neglecting my techie podcasts. You guys are causing me to lose some of my geek creds :-)

Regards... Todd

Peter writes:

I really enjoy twiv and especially twip. The Socratic method to teaching parasitism works for me.

I am an Aerospace engineer but I now work in IT. I am an engineer at heart, but I find parasitology fascinating, and viruses are like little machines, so also fascinating to an engineer.

In your recent TWIP discussion of giardia, you noted that your UV pen is ineffective against cysts because of their low metabolic rate. Or more specifically, I think it was because their DNA was inactive? I didn't know that was a requirement for UV to work. So I wonder, is UV light effective in killing viruses in water?

I seem to recall that radiation is an effective treatment for cancer because cancer cells divide so rapidly. Is that the same effect?



Aaron writes:

Dear TWIV,

I know my last set of questions about ERVs was long, but I'm still holding out hope that you can answer some of them in an upcoming TWIV. I've sent similar questions to several virologists and haven't received any answers.

In the meantime, I have a couple more basic questions where I need some clarification.

I've heard you guys talk about viruses evolving to become less virulent. Could you explain this to me? Are we really saying that the immune systems of their hosts have evolved to resist the viruses rather than the viruses changing something to become less virulent?

My understanding of viruses is that they harm the host merely by reproducing and using up the cell's systems. I understand that very few produce proteins that are actually toxic to the cell. Since viruses consist of only a handful of genes that are dedicated to the production of new viruses, what genes can be mutated to decrease the virulence of a virus? It seems that if one of the viral genes are seriously mutated, the virus will be unable to produce new viable viruses. While that mean the virus is less virulent, it also means the virus will cease to exist.

On the other hand, a virus host is a complex organisms with many genes. A host can experience a mutation in an immunity gene that allows it to resist a viral infection without changing anything else in the host. A virus doesn't have this luxury - any mutation will either cripple it or allow it to sustain its infection - as is the case with HIV. The only "neutral" mutation I can think of in a virus is one that causes it to infect a different cell type. Is this what you mean by a virus evolving to become less virulent? That it now infects a new type of cell that isn't as critical to the host organism?

The way I understand it, a virus is either replicating and causing damage to the host - or it is not replicating and it is latent or eliminate. I'm not sure what the middle ground is where a virus is happily replicating yet is not virulent.

I hope you understand the gist of what I'm trying to say.

Thanks a bunch,



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