Wiping out female malarial mozzies

Malaria threatens half the world’s population. Last year it infected 200 million people and claimed 438,000 lives, mostly small children in sub-Saharan Africa – more than 1,000 die each day in their parents’ arms. The malaria parasite has a knack of rapidly developing resistance to drugs.

The best way to vanquish it is to target the mosquitoes that spread it. Researchers came close in the 1950s with massive DDT campaigns. But DDT was banned in the US in 1972 because of the potent pesticide’s detrimental effects on wildlife and human health.

Now there’s a new approach that’s chemical-free. It works by tinkering with the DNA of the mosquito. That in itself is not new – researchers have been trying to make mosquitoes resistant for decades. The problem is that changing the DNA of an entire population is a slow and uncertain process. This new technique is faster, more reliable and more precise.

The technique, called a “gene drive”, works by manipulating the mosquitoes’ DNA to interfere with the development of females. That’s key because adult females spread the disease by feasting on human blood before laying eggs.

The “driver” in the gene drive is an unusual bit of DNA code that can copy itself from one chromosome to another. While a gene is normally passed on to 50% of the next generation, if it carries a driver it’s possible to transmit it to 100% of the next generation.

Austin Burt and colleagues at Imperial College London have attached gene drives to bits of DNA that hijack and destroy genes crucial to the development of female mosquitoes. According to mathematical models, within 20 generations, or about two years, the gene drive would spread through the population, eliminating females.

The effects of the gene drive can be limited to the species that transmits malaria; the main culprit in sub-Saharan Africa is Anopheles gambiae.

Burt’s team of molecular biologists, population geneticists, anthropologists, policy makers, and community outreach experts has been working for over a decade in three African countries deeply affected by the disease. They work with partners in Africa as a part of Target Malaria, a non‑profit organisation.

When I met with Burt’s team this summer, I was impressed with the iterative way they plan to develop the gene drive mosquitoes, using strict containment measures – first in Britain, then in Africa, mapping out a slow and careful path towards that moment when a bucket full of male mosquitoes carrying the gene drive is taken to a village. They have taken every conceivable safety precaution. Of course, even the safest team can make mistakes, and they will need to closely monitor the effort.

Besides safety, though, there are other ethical issues to be considered.

If gene drives are successful, the benefits to humanity would be enormous. But there could be possible harms.

These concerns range from unintended consequences when a species is eliminated from an ecological niche to the deep unease about the power of science to create and destroy. Ethicists also wonder whether we have the right to eliminate a species.

But should these fears get in the way of using this tool?

I don’t think so. In the 1960s, the world agreed that smallpox was a species worth eliminating. We should feel the same way about A. gambiae.

And isn’t deploying a gene drive that specifically targets the mosquito species that carries malaria far better than using chemical sprays, such as pyrethroids, organochlorines and DDT (still used in some countries) that indiscriminately target any insect?

Finally, who should make these decisions?

Mosquito-borne diseases are no longer just an issue for the poor of tropical countries. With global warming, mosquitoes are expanding their range and with them, the diseases they ferry including malaria, dengue and Zika.

Westerners tend to be preoccupied with the dangers of meddling with the status quo. But if you have lost baby after baby to wrenching fevers, you might think that protecting the status quo is the most unethical choice imaginable.

Gene drives may come to represent one of the most moral gestures scientists have ever made.

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