The HIV centennial

>> Monday, October 06, 2008

It seems that a team of scientists is now estimating the date of origin for HIV as being in 1908. Some impressive hard work went into this that ABC doesn't really touch upon--check out ERV's coverage for more about that.

Still, this actually isn't terribly surprising as a development. Nor does it really change much of anything. But is is interesting as hell. And of course it helps demolish some of the sillier myths that have sprung up about HIV since the virus exploded in the American population in the '80s--you know the ones: that it's a "gay disease" or that SIV crossed into the human population when some dude screwed a monkey, or (of course) the one about "AIDS being God's punishment" for America's sins during... um... during the Reagan Administration and the peak years of the Moral Majority and 700 Club... um... yeah, anyway....

That last bit shouldn't really have needed to be said: anyone who's dumb enough to have believed that AIDS is divine punishment probably also believes The Flintstones is kind of a documentary. (Okay, that link was a cheap shot, but surely you can see why I had to go there. I mean, c'mon! Beer is older than the universe according to these people. Which would actually be an interesting basis for a religion, but that's a matter for another time.)

One reason the age of HIV is interesting is mentioned in the ABC piece: it illustrates something about epidemiology and evolution, and the way in which a virus spreads into its peculiar ecological niche. A virus' ecological niche is an organism; the virus inserts its own genetic code into the cells of the organism and uses those cells to make additional copies of itself, turning each cell into a kind of Xerox™ machine that spits out more-or-less identical copies of the virus.

Now, the thing about this is that a virus' population is limited by its environment unless it can colonize new worlds--i.e. other organisms. And its possible for a virus to create an ecological catastrophe for itself: a virus can consume available resources so rapidly that its world--its host--dies, leaving the virus high and dry. (This is a reason Ebola epidemics have been mercifully brief, at least from a certain point of view: Ebola tends to kill all available hosts so quickly that it fails to spread beyond a fairly small human population.) Lethal viruses are, from an evolutionary point-of-view, failures: they destroy their environments and die shortly thereafter. Less lethal viruses (or nonlethal ones) last long enough to colonize new worlds--new hosts, in other words--and therefore succeed in passing along their genetic material for longer and longer intervals of time.

We think of HIV as being particularly nasty and fatal because the disease it causes, AIDS, is so deadly, and perhaps worse yet, is mean, often turning the victim into a pale shell of a person. The irony is that HIV itself isn't actually all that fatal: it may spend years or decades slowly colonizing an environment (the person it has infected), and if that person develops AIDS and dies, he or she isn't directly killed by HIV but by the opportunistic infections that move in or undergo a catastrophic population explosion of their own as a side-effect of HIV wrecking its environment's immune system.

A virus' ability to colonize new worlds--to leap the spaces between one host and another--is dependent on several factors, but the ones we can pay attention to right now are population density and transmissibility. HIV is not actually readily transmissible: it requires an exchange of fluids and dies within hours when dried. Under the circumstances then, the only way for HIV to have a good chance of colonization is if there are a lot of people (unintentionally) doing their best to spread the disease. This is part of the reason you have a virus that nobody sees for eighty to a hundred years: completely aside from diagnostic difficulties, HIV isn't even found in human populations large enough to insure frequent spread of HIV colonies from host to host until urbanization and globalization bring new worlds within the virus' reach.

So, it's not a surprising development, but it's an interesting one, and an illustrative one.


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