Wednesday, October 12, 2005

Beating malaria

Malaria kills more than a million people a year, most of them children under the age of 5 in sub-Saharan Africa. Hundreds of millions of people have the disease, in varying degrees of severity.

The agent of infection is a nasty little parasite named Plasmodium falciparum that requires two other species to complete its life cycle: the Anopheles mosquito, and the primate Homo sapiens.

That's us.

Plasmodium doesn't bear us any grudge. From the parasite's point of view, we are a necessary blob of meat in which to breed.

Here's how it works.

An infected female Anopheles mosquito bites a human and injects parasites into the victim's bloodstream. The parasites make their way to the liver and multiply. The teeming parasites explode from the liver cells back into the bloodstream, where they invade red blood cells and multiply again. They fill the cells to bursting, then invade more red blood cells. Again. And again. The malaria victim sustain bouts of fever with each cycle of cell infection.

If an uninfected female Anopheles mosquito bites an infected human, she sucks up parasites with her blood meal. These multiply in her stomach wall, then make their way to her salivary glands, ready for transfer to another human.

And so it goes, around and around -- human liver, human blood, mosquito stomach, mosquito salivary gland. Each stage of Plasmodium's life cycle involves a specialized form of the parasite. No other hosts will do but Homo sapiens and Anopheles. All of this can be given a plausible evolutionary explanation. If it's to be explained by "intelligent design," the designer must really have had it in for humans.

A team of scientists at Imperial College London now think they can break the cycle. They have added a jellyfish gene to the mosquito's genome that makes the testicles of male larvae glow fluorescent, allowing them to be mechanically separated from otherwise identical female larvae, sterilized, then released into the wild as adults. Release enough infertile males to mate with females and a natural population will collapse.

Now the story becomes political. Any attempt to release genetically-modified organisms into the wild is controversial. The promises and perils of genetic engineering test the wisdom of nature's only moral species, and the decisions are too important to be left to scientists alone. The best insurance that this new power will be used wisely is a citizenry solidly educated in science. Real science. The science of cause and effect.