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It's inevitable. It's right out of Darwin. There's a struggle (by the disease pathogens) to survive, a threat to survival, and genetic differences among the pathogens which leads to differential survival potential in face of that threat. Necessarily, the specific organisms best equipped to resist that challenge are the ones most likely to reproduce, which means that the next generation is fractionally less vulnerable to the threat, that being the drug being used. After development of Penicillin (which was not, as some people think, the first antibiotic; that title belongs to Sulfanilamide) it was thought that we'd entered a golden age of medical treatment where diseases like Syphillis and Streptococcus would be eliminated. Then disillusionment set in as drug resistant strains appeared. When you're talking about bacteria, the problem is compounded. For many fungally-derived antibiotics, there is a single gene which can appear which grants its carrier near immunity to the effect of that antibiotic. After all, the fungi have been using these chemical weapons for a long time and the bacteria have had plenty of time to evolve defenses. And though they are not sexual beings, bacteria have a mechanism for exchanging genetic material. Two of them which touch each other may temporarily fuse their cell membranes and randomly trade genes, then separate again. And this can happen between bugs of radically different species. If one which carries the resistance gene for Penicillin conjugates with one which carries the resistance gene for Neomycin, afterwards one of them may carry both genes away and reproduce. One of those may then pick up the resistance gene to Streptomycin, and then reproduce further. Do this enough times and you've created a super-bug which is resistant to all of them. This has already happened. There now exists a strain of Tuberculosis for which there is no treatment available; it's resistant to all known drugs. There's also an untreatable version of Gonorrhea going around. Happy days, eh? But it's not just bacteria which do this; viruses mix their genes too, though they're not as good at it. Influenza is a classic example of this. Actually, it may surprise you to learn that you can only get the flu once. Afterwards, your immune system is sensitized, and that particular strain of flu will never infect you again. The reason you keep getting sick is that each time it's actually a new disease, sufficiently different that the previous antibodies won't stick to it, so your body has to fight the new one from scratch. Mostly they're just variations on the same theme, but every ten to thirty years a really quite different strain comes out which is particularly potent and kills a lot of people. (The classic example of this was the influenza of 1918, which actually killed more people than died in WWI at the same time. I remember being sick as a dog from Hong Kong Flu when I was in college, another one of the super-flus.) For a long time they wondered where these came from, and recently the problem was solved. There's a form of influenza which infects geese and ducks. Humans can't get it, and geese and ducks can't get the human form. But genetic analysis showed that these human super-flus seemed to have genetics borrowed from the goose version. How could this happen? It turns out that pigs can get both versions. If pigs, geese and humans all live in close proximity to each other, and if a pig gets both at the same time, then there may be cells inside that pig where both kinds of viruses are trying to reproduce simultaneously. When that happens, hybrid viruses may get built carrying genes from both strains. Most of those will be useless, of course, but once in a while the resulting virus will be a new superbug. It's a very low probability event, of course, but with trillions of viruses being produced every day it's bound to happen eventually -- like every ten to thirty years. They have now traced the last few superbugs back and found that they come out of rural China, where people do live in close proximity to both swine and geese. And with the invention of jet travel, the entire world became one big Petrie dish for diseases. When a new strain of flu pops up, it will be everywhere in the world in less than two years. It's been known for a long time that HIV is particularly mutable, and so it should come as no surprise that drug-resistant forms have appeared. Equally, evolutionary theory strongly implies that in the face of drug adversity that the resistant strains will have an advantage and will spread. So it is no surprise to learn that about a quarter of HIV cases in San Francisco now are indeed untreatable with current drugs and that this may break above half within just a few years, since having HIV doesn't prevent you from becoming infected with new strains. This reinforces the fact that the only viable long term strategy for HIV is prevention. The fact that there are drugs available shouldn't make anyone complacent. Everyone must continue to practice "safe sex". Doing otherwise not only risks your own life, but the lives of the people you love most. (discuss) |
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