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The Ecology of AIDS
Can our sexual practices alter
the very evolutionary path of a virus?
Copyright 1995 by Lynna Landstreet. This column originally appeared in Xtra magazine. Published by Pink Triangle Press, 491 Church Street, 2nd Floor, Toronto, Ontario, Canada M4Y 2C6.
he wheel of the year is turning again, and the onset of bitter winds and long nights always starts me thinking about death. It's partly because Samhain, the original name for Halloween, is a Celtic holiday devoted to honouring those who have died in the past year, and partly just the general atmosphere of decay and decline that prevails around now, but it never fails. And a recent university lecture about AIDS has added fuel to the fire.
Like many a recession casualty, I've taken the plunge back into academia. It wasn't just the abysmal job market; I'd always wanted to, but had been a little too attached to having some disposable income to want to dive back into student poverty. Disposal income is now a distant memory, however, and grad school offered the opportunity to remain equally broke while regaining a small portion of my self-esteem. Thus, I find myself working on a Master's degree in Environmental Studies.
One of my favourite courses so far is the introductory ecology course taught by Laurence Packer, who recently illustrated the topic of disease with an example that hit close to home for many of us: the evolutionary biology of HIV. It was a fascinating, and slightly unsettling contrast to the contexts in which I'm used to discussing AIDS -- as political issue, as health crisis, and as the reason I've lost so many friends.
One interesting point was that the virus's rapid mutation rate means that it can actually evolve over the course of one person's struggle with the disease, becoming a qualitatively different organism by the end of the victim's life than it was at the time of infection. Statistics bear this out -- people infected by someone with full-blown AIDS die faster than those infected by someone more recently exposed. The virus they encounter has not only mutated to become more virulent, but may also have evolved an immunity to antiviral medications.
The virus's long incubation period before activating is a result of natural selection -- since HIV spreads less easily than most diseases, quicker-acting strains that killed off their host before he had a chance to pass it on would never have survived long enough to pass on their genes. Thus, the slower-acting strains initially became predominant.
That changed when the virus reached the North American gay community, where frequent, unprotected sex was common. Suddenly a fast-acting, highly virulent form of the virus could do just fine, and the balance between the strains began to shift. Remember how back in the '80s, AIDS educators used to emphasize that many people who tested HIV positive would not go on to develop full-blown AIDS?
But when safe sex became the norm, the balance shifted yet again. Now, once more, a highly virulent form of the virus may never have the chance to spread before its host dies. So, by natural selection, the more benign forms are making a comeback. Which is not to say we'll see AIDS become non-fatal by next week, but gay men with AIDS are already living longer than hets, IV drug users, and other populations where safe sex isn't as common.
It's an interesting thought: when you put on that condom or glove, you aren't just protecting yourself or your partner, you are altering the evolutionary path of the virus itself. Kind of makes you feel like God -- or Gaia.
But perhaps the most interesting insight in the lecture was that we may be taking the wrong approach in trying to develop an HIV vaccine -- or indeed, in disease vaccines in general. Viruses and bacteria do mutate, some faster than others, and no vaccine will ever be able to offer complete protection against a rapidly evolving disease organism. Influenza mutates less quickly than HIV, and the flu vaccine is still hit and miss.
A more effective approach might be to try to immunize people against the toxins that viruses produce, rather than the viruses themselves. That way, not only could we be exposed to the virus the toxins come from without harm, but we would also, by that exposure, gain immunity to related viruses, even new strains -- just as exposure to chicken pox grants partial immunity to smallpox.
That, coupled with the evolutionary constraints already imposed by safe sex, might mean that HIV, while it will probably never disappear, could one day become as harmless as the many other microorganisms that inhabit our bodies without disturbing their functioning one bit.
A reassuring thought, on the eve of Samhain, as we once more bid farewell to those we've lost.
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