When an Aedes aegypti mosquito bites you, she – because only the females, which need blood as nutrients for their offspring, bite – will probe your skin with her proboscis as many as 20 times.
Two pairs of sharp cutting edges, the fascicle, break the skin and then search for a blood vessel, withdrawing and re-entering until a suitable target is found. When the blood starts to flow, a salivary tube delivers a protein that stops it clotting.
The mosquito holds still and then begins to suck; in 90 seconds’ time, she feels full, and stops. And then, if you are in parts of South and Central America and bang out of luck, you will have Zika.
Workers fumigating a Zika outbreak in Caracas, Venezuela. Photograph: Xinhua/Rex/Shutterstock
It’s a horrible idea, and one that will draw shudders from anyone who has ever been bitten by a mosquito – which is to say, just about everyone. In the entire animal kingdom, the mosquito occupies a special place as receptacle for our hatred and disgust. Even the great and generous EO Wilson, author of the touchstone argument for preserving biodiversity, The Creation: An Appeal to Save Life on Earth, makes an exception for anopheles gambiae, which spreads malaria in Africa. “Keep their DNA for future research,” he writes, “and let them go.”
When Wilson thus hardens his heart, he speaks for us all. Where we revere and anthropomorphise such brutal predators as sharks, tigers and bears, we view these tiny ectoparasites as worthless, an evolutionary accident with no redeeming or adorable characteristics. No one ever had a cuddly mosquito. Thanks to malaria, they have probably helped to kill more than half of all humans ever to have lived.
Today, according to the Gates foundation, the diseases they carry kill about 725,000 people a year, 600,000 of them victims of malaria. They are, as such, the only creature responsible for the deaths of more humans than humans themselves; we only manage to kill about 475,000 a year. This deadly work is carried out all over the planet: mosquitoes are found on every continent except Antarctica.
And now there is Zika, which can lead to microcephaly and its associated physical deformities in unborn children, and for which there is no vaccine. This new horror has prompted fresh attention to the vexed question of how to defeat them. And that consideration leads to an unsentimental thought that we would entertain about no other creature: can’t we wipe them off the face of the Earth?
Watch a video explaining the Zika outbreak.
“I don’t think most people would have any qualms about totally eliminating them,” says Professor Hilary Ranson, head of vector biology at the Liverpool School of Tropical Medicine. “I spend most of my time trying to keep them alive and study them, but that’s in order to try to kill them. Ultimately I wouldn’t be too sentimental.” Professor Steve Lindsay, a public-health entomologist at the University of Durham agrees: “I have no problem with taking out the mosquito.”
In reality, as Lindsay and Ranson are quick to point out, the total extinction of all mosquito species would be as senseless as it would be impossible. Of the 3,000 varieties on the planet, only 200 or so bite us; only Aedes aegypti, and perhaps the more common Culex quinquefasciatus, are thought to carry Zika. Besides, as Jules Pretty, professor of environment and society at the University of Essex, points out: “In lots of environments, especially the Arctic north, where their abundance is utterly dispiriting, they are a vital source of food for animals higher up the food chain.” A total mosquito apocalypse would be a catastrophe.
But what about a narrower specicide, wiping out Aedes aegypti, and dealing a devastating blow to Zika, dengue fever and chikungunya alike? Well, that might be much more desirable – and much more achievable. “We’ve got really good new weapons,” says Dr Jo Lines, reader of malaria control and vector biology at the London School of Hygiene and Tropical Medicine. “There are extinction options. It wouldn’t be easy, but we shouldn’t forget about it.”
For Lines, there is a more pressing case for the eradication of aegypti, as a carrier of dengue fever, than any other species of mosquito. “There is no visible end to this except a war against aegypti,” he says. “Otherwise this is going to go on for a thousand years.” He points out that because aegypti are thoroughly adapted to a man-made environment, unlike the anopheles variety that carry malaria, they will only become more prevalent as the human population and its accompanying urban sprawl grow. “The other things we’ll build out. West Nile, malaria … but this is not going to fade away. These things are like rats and pigeons. We give them their home and food.”
So how, exactly, would we go about it? For the specicide advocates, the most promising means of attack lies in a cutting-edge technology known as a gene drive, the subject of much excited reporting in recent weeks. And no wonder, so seductively dystopian is its premise: that a species can be eradicated by altering the genetic code of males in captivity so that they will only be able to produce sterile offspring, then releasing them into the wild to mate with unsuspecting females, rendering the next generation barren. Oxitec, a British company that has pioneered this kind of genetic modification, has been conducting trials since 2009, and has a production facility in Campinas, Brazil. And it is not alone.
“It really has been a gamechanger,” says Andrea Crisanti, professor of molecular parasitology at Imperial College London. “We are able to modify the gene with unprecedented precision and flexibility.” Crisanti, a leading expert in the field, has focused his own work on a similar mechanism that fights the malaria-carrying Anopheles gambiae, but he says that it could be exported to other species as well. “There are lots of advantages. If it doesn’t work, nobody has to worry: if they can’t breed, the GM is selected out. If it works, in theory you have total extinction. And if people are concerned about that, you can keep some in the laboratory and reintroduce them. So it is totally reversible.” He gives a small laugh, and sounds freshly amazed at the power of the technology at his fingertips. “We can edit nature,” he says. “This is an incredible new development.”
There are practical impediments to this plan at the moment, though. “The number of sterile males you’d have to release is just phenomenal,” says Ranson. All the same, the approach could make huge inroads in controlling the population, and extinction may be a realistic goal. Crisanti acknowledges the risks that his work brings with it. “But on the battlefield of risk-management, you have to accept that any measure has a risk to be balanced against the benefit. There is a risk we all rush, and that shouldn’t be done. We shouldn’t implement this on an emotional basis just because we don’t have anything else. And we shouldn’t take shortcuts in the regulatory process. We don’t want it to backfire when it could be a gamechanger for public health.”
Still, talk of “editing nature” will unnerve those who are naturally suspicious of such radical moves, and for whom the term “genetic modification” is an automatic red flag. Some fear that the precise effects on the mosquitoes’ ecosystems are still hazy (while they might be our nemeses, there are fish that think they’re delicious). But most biologists are confident that such fears are misplaced. “Ecosystems would adapt,” says Ranson. “There are so many similar mosquito species that don’t transmit disease that something else would fulfil that niche without doing any major harm.”
Lines agrees: “Everywhere they exist, apart from parts of east Africa, they are an invasive species. So getting rid of them would be a boon to the ecosystem. What are the local things that eat aegypti that might say, ‘Now we’re hungry’? Well, there are fish and insects that eat the larvae and bats that eat the adults, and birds and geckos, but all of those predators have got other things to eat.”
For others, the attention-grabbing qualities of a genetically modified mosquito spreading its poisoned seed are a source of more frustration than wonder; a distraction from on-the-ground efforts that could make a substantial difference in the fight against Zika and dengue fever right away. “What it mainly is is irritating,” says Lindsay. “Everyone talks about vaccines and GM, but actually we can control this vector by much simpler means.” Lindsay points out that aegypti were eliminated from much of South America in the 1960s by the simple mechanism of spraying containers with oil, kerosene and, later, the controversial pesticide DDT. Today, with a much larger human population and some pesticide resistance, that process is much more difficult; above all, the growth in the population of aegypti is down to our rapid increase in plastic consumption; it provides the mosquitos with an ideal breeding ground.
“There is so much misinformation out there,” Lindsay says. “You see pictures of large open areas of stagnant water. But that’s not where the danger is. This thing breeds in small containers: flowerpots, gutters, tyres, water bottles. It’s about screening buildings, putting up nets, spraying insecticide in laundry areas. That’s not something for health professionals: that’s about educating and empowering communities so that they can reduce the risk themselves.” So vexed is Lindsay by the way this crucial message is, in his view, being drowned out, that he and a group of colleagues have written a letter to the Lancet, shortly to be published, urging a renewed focus on these less exotic measures. “We have tools available,” it reads, “that we can use to defeat this mosquito vector today.”
Professor Trudie Lang, a senior research fellow at Oxford and head of the Global Health Network, tells a similar story. Her research is focused on improving public health, and connecting researchers and health workers in developing countries. It is, again, an unglamorous specialism – but a critical one, for the fight against Zika as much as anything else.
“There’s this incredible study on foetal scans and baby measurements,” Lang explains, “which will mean that at least people can interpret the scans properly; if the problem is with foetal development then we have to know how that occurs. But these kinds of big studies are really underfunded, and because this kind of research doesn’t get any attention, that’s why we are where we are with Zika. The really hi-tech, GM stuff – bring it on. Marvellous. It gets people excited, it gets the [research] papers in Nature. But the normal, everyday stuff – the pragmatic, frontline research – can make some of the biggest differences. And it’s very, very difficult to get funding to support research-capacity development.” Read the deadly last three words of that quote and you will see exactly where the problem lies. “The trouble,” Lang says with a sigh, “is that it just isn’t sexy.”
It is hard to prove a direct causal link between the exoticised enthusiasm for wiping out a species on the one hand and the underfunding of such crucial work on the other. All the same, there is a certain bitter irony that in an attempt to beat a disease whose impact will be felt most keenly by women and their unborn children, and which has been exacerbated by a shortage of funding for studies that would focus on the wellbeing of women in developing countries, we are contemplating a macho solution that entails sending male mosquitoes to impregnate as many females as possible, with the ultimate ambition of wiping the enemy off the face of the Earth.
Whatever the priorities, no scientist disputes that if the technology were to be perfected, the gene-drive plan would be a remarkable boon to public health. Yet there may be other, more abstract, objections contained in the eerie idea of that word: extinction, the permanent eradication of a species that has evolved and survived for thousands of years. Melanie Challenger, author of On Extinction: How We Became Estranged from Nature, travelled from England to South America to the Antarctic to think about how we contend with the elimination of the species. “Is there a more intrinsic philosophical reason why we shouldn’t drive an animal to extinction?” she asks. “My instinct is: yes. If a part of our brain lights up with caution, that’s a really good instinct, and we should heed it. I don’t think ‘love of nature’ is a good reason not to do it. But I do think there’s something more robust: the sanctity of life. If you start getting cavalier about the existence of a living being, if we start to think it’s OK to eradicate something because it’s a threat to us, we put other ideas about the sanctity of life in question. And because that’s ultimately an artificial, human concept, it needs to be cherished.”
Yet even Challenger acknowledges that such arguments might seem a bit abstract to the mother of a child who will be deformed because of Zika, or killed by malaria. “I’m a mum,” she says, “and no one can understand more than a mother the heartache and importance and power of keeping your children alive.” Crisanti has a ready riposte to such abstract concerns: if we had already wiped out aegypti, would we ever contemplate reintroducing them? “When you reverse the argument,” he says, “I think it’s clear.”
In the end, if the technical and ecological objections can be overcome, it seems unlikely that philosophical arguments for the sanctity of aedes aegypti will hold sway. The mosquito has so ravaged us, for so long, that for most people it has exhausted all rights of appeal. Pretty, whose work straddles the arts and sciences, has also written about extinction. In his book, The Edge of Extinction, he considers how different cultures deal with the loss of species and habitats that surround them. It is fair to say that he is an advocate of conservation. But even he has his limit. “If one has a hierarchy of thoughts,” he says, “the first would be that it would be desirable if we humans had a lighter impact and that any loss is one that should be deeply worrying. And in most cases you can stop at that point. But here you can ask the second question: if there was a loss of a whole species, would there be a human benefit? And in this case, the human benefit is so great that I think you have to say: ‘OK, I can hold these two thoughts at once.’”
This article was first published by The Guardian on 10 Feb 2016.
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