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Politics

Insecticide

It was a typically anodyne statement by the World Health Organisation: “Given the magnitude of the Zika crisis, WHO encourages affected countries and their partners to boost the use of both old and new approaches to mosquito control.” Anodyne, that is, until you realise what they mean by “new approaches”.

Zika is a mosquito-borne virus that is spreading panic around the world. It was first linked to hydrocephaly – a developmental defect in infants that results in abnormally small heads, severe learning difficulties, and often early death – only last year in Brazil. WHO estimates that it may infect 3 to 4 million people in the Americas alone this year – and its “new approach” is to exterminate the mosquitoes. Literally.

An alternative approach would be to develop a vaccine for the Zika virus – but that would take up to ten years, and the crisis is now. Zika has already been detected in 30 countries, and Brazil is investigating more than 4,300 suspected cases of microcephaly. The pressure is on to do something fast.

By the wildest of coincidences, something fast is available. It’s only twelve years since Austin Burt, an evolutionary geneticist at Imperial College in London, raised the idea of a “gene drive” that would spread some desirable quality (like immunity to malaria) through an entire population in a relatively short time. With a population of mosquitoes, whose generations are only a month long, you could do it in only a year or two.

Mosquitoes were the obvious first target for the new technology, since their bite transmits lethal diseases like dengue fever, chikungunya and, above all, malaria, which still kills 600,000 people a year. But “editing” a gene was a long, difficult process until CRISPR/Cas9, a fast, accurate, cheap gene-editing tool that was developed in 2012.

Scientists immediately set to work on mosquito genes, and by last year they had a genetically modified (GM) mosquito whose offspring do not survive into adulthood. They die as larvae, before they can breed.

By an even wilder coincidence, the species of mosquito whose genes they edited was Aedes aegypti, best known as a vector for dengue fever. But Aedes aegyti is also the main transmitter of the Zika virus, and Oxitec, the British-based company that was created to exploit this new technology, is already field-testing the GM version of the insect – in Brazil, as luck would have it.

In the town of Piracicaba, Oxitec has a “factory” that produces 800,000 mosquitoes each week that carry the OX513A gene, and a white van that sets them free all over town. In theory they should mate with the local females of the same species, whose children will never grow up to mate themselves, so the local population should go into steep decline. And in practice, it works.

It’s actually a rather labour-intensive process, and the little prototype “factory” is only producing enough GM males to cover a town of 10,000 people. To completely eradicate the local population of Aedes aegypti would take several dozen generations – that is, a couple of years – even if it was not replenished by fertile males from the surrounding area.

Obviously, the enterprise could be scaled up to cover all of Brazil, or even the whole world. The question is: should it be?

Human beings have wiped out entire species in the past, starting with the big animals that were wiped out in the “New World blitzes” when human hunters first arrived in the Americas, Australia and various ocean islands. But we never actually intended to exterminate a species before. This time it’s different.

Some environmentalists have already attacked the idea, ostensibly on the grounds that removing an entire species of mosquito would upset the ecological balance and possibly cause further extinctions among the animals that feed on them, or maybe open up an ecological niche that would be filled by an even nastier species.

But one suspects that their real worry is the “slippery slope”. If we edit Aedes aegypti out of existence today, what species will we next choose to remove for our own convenience? That is a legitimate concern, but nothing can make mosquitoes cuddly, whereas healthy babies definitely are cuddly. The threat of Zika will trump all their arguments.

Besides, there are some 3,000 species of mosquitoes (only 200 of which bite human beings), so some other species will just fill the niche left empty by Aedes aegypti and no other bird, fish or insect will go hungry. If you are still upset about “playing God”, keep a small breeding population of Aedes aegypti alive in captivity so you can repopulate the planet with the little pests if you need to.

The great American biologist and champion of biodiversity E.O. Wilson gets the last word on this. In his book “The Creation: An Appeal to Save Life on Earth”, he makes a exception for Anopheles gambiae, the mosquito that spreads malaria in Africa. “Keep their DNA for research,” he writes, “and let them go.”

The same goes for Aedes aegypti. We are going to commit insecticide. And we should.
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To shorten to 725 words, omit paragraphs 5 and 9. (“Mosquitoes…2012″; and “It’s actually…area”)