Monday, June 25, 2007

Malaria and Evolution

Now, National Geographic has, for their July 2007 issue, chosen Malaria as the main topic. Now that's a highly interesting article, and you should read it when you have the time. However, there's some more evolution that's in this issue. Back in the mid 1900s, things were looking bad for malaria:

The global eradication effort did achieve some notable successes. Malaria was virtually wiped out in much of the Caribbean and South Pacific, from the Balkans, from Taiwan. In Sri Lanka, there were 2.8 million cases of malaria in 1946, and a total of 17 in 1963. In India, malaria deaths plummeted from 800,000 a year to scarcely any.
Unfortunately, we stopped caring, and some horrific consequences resulted:

In several places where malaria had been on the brink of extinction, including both Sri Lanka and India, the disease came roaring back. And in much of sub-Saharan Africa, malaria eradication never really got started. The WHO program largely bypassed the continent, and smaller scale efforts made little headway.

Soon after the program collapsed, mosquito control lost access to its crucial tool, DDT. The problem was overuse—not by malaria fighters but by farmers, especially cotton growers, trying to protect their crops. The spray was so cheap that many times the necessary doses were sometimes applied. The insecticide accumulated in the soil and tainted watercourses. Though nontoxic to humans, DDT harmed peregrine falcons, sea lions, and salmon. In 1962 Rachel Carson published Silent Spring, documenting this abuse and painting so damning a picture that the chemical was eventually outlawed by most of the world for agricultural use. Exceptions were made for malaria control, but DDT became nearly impossible to procure. "The ban on DDT," says Gwadz of the National Institutes of Health, "may have killed 20 million children."
As much as I'd hate to put down Rachel Carson, she really did cause a large uproar against DDT. Perhaps a bit too large of one, which kept DDT from being used in places where it would have been helpful. But here comes the worst part of it:

Then came the biggest crisis of all: widespread drug resistance. Malaria parasites reproduce so quickly that they evolve on fast-forward, constantly spinning out new mutations. Some mutations protected the parasites from chloroquine. The trait was swiftly passed to the next generation of parasites, and with each new exposure to chloroquine the drug-resistant parasites multiplied. Soon they were unleashing large-scale malaria epidemics for which treatment could be exceedingly difficult. By the 1990s, malaria afflicted a greater number of people, and was harder to cure, than ever.
Oh, would you look at that? In just a few decades, our most powerful medicines were rendered useless. Chloroquine was considered one of the greatest achievements in the fight against malaria. It was a synthetic, highly effective, and cheap cure for malaria. Now it's nothing! Now. evolution is a powerful force which should be given credit to, not denied. And don't give me that "microevolution" bull. There's another characteristic of malaria which paints it's evolution on a very macro level indeed:

The disease has been with humans since before we were human. Our hominin ancestors almost certainly suffered from malaria. The parasite and the mosquito are both ancient creatures—the dinosaurs might have had malaria—and this longevity has allowed the disease ample time to exploit the vulnerabilities of an immune system. And not just ours. Mice, birds, porcupines, lemurs, monkeys, and apes catch their own forms of malaria. Bats and snakes and flying squirrels have malaria.
Since dinosaurs, mice, birds, porcupines, lemurs, monkeys, apes, bats, snakes, flying squirrels and humans all have similar immune systems, therefore they're all exploitable by malaria. Why couldn't an intelligent designer spare some of these species by giving them a different immune system? Was he/she/it just too lazy to do so? Well, thanks a lot!

(Hooray for Panda's Thumb)

1 comment:

Naboerne said...

Some may think that DDT was the solution for eradicating malaria, but that is not the case. Eradicating moquitos is impossible. The insect is many 100's of million years old and has survived larger catastrophies.
But stop a moment and think. The malaria parasite need both mosquitos and humans to survive. If we could treat all malaria cases, then humans wouldn't be a source and the mosquitos wouldn't become infected.
Malaria parasites are species specific, so you are not in risc of becoming infected by bird malaria etc..
Resistance is a gentic advantage where one or two parasites that genetically are able to break down the drug used. Under normal conditions this is not an advantage, but when drugs are used, the advantage is considerable. The sensitive parasites are killed leaving the resistant parasites to thrieve. By treating patients here and there we enable the resistant parasites to develope.
If we could treat the whole population at once, the few resistant parasites would be killed by the immunesystem.