Health & Wellbeing

Genetic genocide: Genetically altered mosquito warriors could wipe out humanity's biggest killer

Aedes aegypti, the #1 disease vector for dengue fever (Photo by Muhammad Mahdi Karim, published under the GNU free documentation license)
Aedes aegypti, the #1 disease vector for dengue fever (Photo by Muhammad Mahdi Karim, published under the GNU free documentation license)
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Population crash results from field tests by James et. al.
Population crash results from field tests by James et. al.
Aedes aegypti, the #1 disease vector for dengue fever (Photo by Muhammad Mahdi Karim, published under the GNU free documentation license)
Aedes aegypti, the #1 disease vector for dengue fever (Photo by Muhammad Mahdi Karim, published under the GNU free documentation license)

War, plague, famine, heart disease, cigarettes, road trauma: six very effective killers of human beings. But they're all amateurs when their records are compared to the number one mass murderer of all time. The humble mosquito, and the deadly diseases it carries, is estimated to have been responsible for as many as 46 billion deaths over the history of our species. That staggering number is even more frightening in context - it means that mosquitoes are alleged to have killed more than half the humans that ever lived.

So if any creature has earned the full force of the wrath of humanity, this nasty little bugger is it. Especially certain species like Aedes aegypti mosquitoes - the world's number one disease vector for deadly dengue fever, which infects between 50 and 100 million people a year around the world.

A. aegypti has evolved into the most curious and innocuous of human predators - it's the females that bite, and they more or less only feed on humans. Each bite exposes the victim to any blood-borne pathogens that the mosquito might have picked up along its way. Dengue and yellow fevers are among the most common - the mosquito contracts the virus by biting an infected victim, and then injects it along with its saliva when it stabs the next unlucky target's skin with its proboscis.

A. aegypti flies silently, so it's hard to know when you're in danger of being bitten, and it breeds and multiplies extremely effectively, needing only a teaspoon full of standing water for its larvae to hatch.

DDT-based insecticides have been effective against these little blighters, but evolution is quickly building up their resistance to this and other control measures. Fighting them with poison might be effective in the short term, but in the long run it only makes them stronger.

There is, however, a potential solution that can hijack the mosquito's breeding cycle to dramatically bring down the population and human risk factors. And it's undergoing testing in two very different ways right now.

Genetic hacking - a brilliant solution

American scientist Anthony James, from UC Irvine, has made mosquito genetics the focus of his career - and his latest invention is a genetically modified mosquito designed to bring populations of Aedes aegypti down from within.In short, the modified genes affect only the female mosquitoes, rendering them flightless. The larvae hatch on the water, and the females are unable to leave, rendering them harmless to humans and leaving them to die. The males are unaffected, so they mature normally, then mate with other females to pass the genetic modification on.

It's an extremely effective way of triggering a mosquito population crash - James and his colleagues have proven in cage-based testing in Mexico that a sufficient number of genetically hacked males can completely decimate a mosquito population within a few months. The table below shows this genetic genocide in action - within 23 and 33 weeks, the genetically modified males managed to completely destroy the otherwise stable mosquito population in James' test cages.

Population crash results from field tests by James et. al.
Population crash results from field tests by James et. al.

A. aegypti eggs make this a fantastically portable solution too - they survive for years at a time in dry conditions, then hatch in the presence of water. So you can more or less post an envelope full of millions of dry eggs to wherever in the world it's needed, and just add water. The crippled females will die where they hatch and you've got yourself a mutant force of GM males ready to start their work.

Genetically modified mosquitoes to the wind

But while James' "netted laboratory" follows the traditionally cautious scientific approach, one of his partners has been decidedly more gung-ho about it.Luke Alphey, whose company Oxitec was originally hired by James to design the flightless female genetic modification, is so confident that these genetic warriors work, and that there will be no environmental ill effects, that he has taken advantage of the lack of regulation in many areas to conduct full scale field tests in the wild.

Oxitec's historic first release of GM mosquitoes in 2009 killed an estimated 80% of the A. aegypti population on the Grand Cayman island in the Carribbean - a geographically isolated area.

More mutant, autocidal mosquitoes have been released in Malaysia, and the technique is reportedly going into large scale production in Brazil.

James sees Oxitec's full-speed-ahead approach as a potential risk to the entire science of genetic modification. "That's the difficulty of working with corporations," he told Scientific American, "I can't control corporate partners."

An ethical and environmental quandary

So it seems it's happening. And whether it's for better or for worse depends entirely on your viewpoint.It's difficult to know exactly what the result might be when you release something like this into the wild. Will there be knock-on effects on the food chain? What will the birds and fish that feed on mosquitoes eat instead? Will the demise of A. aegypti make way for an even nastier pest? Will their removal take away the means of pollination for certain plants? And will the genetic modification itself have unforeseen repercussions down the track?

Then there's the ethics of it - advanced use of this technology could foreseeably cause A. aegypti to become extinct. Some people brave the antarctic winter to save endangered whales, others will chain themselves to trees to defend endangered frogs... But who will stand up for the mosquito? And with a world human population ticking past 7 billion and counting, should we look at A. aegypti as an effective and necessary form of human population control?

On the other hand, humans have become dominant on this planet chiefly due to our ability to manipulate our environment - and with a scientific consensus forming that the complete eradication of mosquitoes would have limited, if any, adverse environmental effects, this could be one of the most human-friendly modifications we could make to our world. And it would certainly be no worse for the environment than our habit of clear-felling forest areas.

As for "playing God" - that argument is moot. We're well and truly adept at that. We've been artificially selecting animals and plants for hundreds and thousands of years to suit our visual, olfactory and gastronomic preferences. Hardly a species that enters our lives in a significant way has not been altered over the generations to suit us better.

Why should we spare our most dangerous natural predator? Does history's greatest killer of human beings deserve a reprieve from the death penalty? What do you think?

Chris Coffey
Thoughtful article rather than a re-write of a press release - nice work Loz! I don\'t know what the answer to the GM quandry is, but fascinating to know that it\'s already in use in the animal world at large. I\'ll be watching this space...
Jamie Estep
I can\'t stand mosquito\'s but looking at this from a scientific standpoint, how can anyone suggest that there will be no negative repercussions by eradicating them all. If mosquito\'s have accounted for or have been part in half of all human deaths over our existence, then they have no doubt played a huge role in our evolution over the entire course of it. The repercussions on the environment may be negligible, but seriously, we can\'t predict the weather, how can we predict the effects of wiping out an entire species that\'s been here for millions of years. And as for the playing god argument, we\'ve also messed up just about every eco system on the planet. The coral reefs are a mess. There\'s virtually no more sharks on earth. The rainforests are slowly but surely being deforested into oblivion. Big cats, rhinos, elephants, tuna, hundreds of others are on the verge of extinction. I guess you could say, what\'s the harm in one more species... When the only consequence we can see in doing something like this is the immediate one, there\'s bound to be problems as a result of it later on. Humans never get things right the first try. We spend the rest of time trying to compensate for our errors.
Paul Schacht
Kinda like \"Nuke \'em till they glow and shoot \'em in the dark!\", but without all the nasty radioactive side effects. Since every human being doesn\'t think twice about swatting every mosquito within reach, I think the ethical question was decided a long time ago. In fact, our fight or flight genetics pretty much demand that we eliminate threats to our survival.
Since my daughter died of malaria when she was 16 a rather long time ago, I have a somewhat vested interest in seeing anything that reduces the death toll caused by the mosquito. Since DDT was banned there has been an upsurge of fatalities caused by the mosquito, now we have a way to fight back ao I say - go for it, and may mankind win!
Ce D
First crops, now insects, next rodents, then livestock, primates and of course ourselves. I stopped reading horror fiction because I find reality is much more frightening.
Timothy Neill
We don\'t need a population control device that is so arbitrary, cruel and mindless as disease, when we are capable of doing the job with something as simple as Female Literacy. Forcing backwards cultures to educate women would control overpopulation within one generation, and allow exploitation of an abundant untapped resource in those regions, namely the imagination, talent and labor of the female half of humanity. There is a good reason some nations are so poor, and until they recognize the true value of women, I think they will stay that way. I don\'t know that we are intelligent enough to decide the fate of a species. Doubtless there are consequences that we can\'t imagine until they come about, however, I am pretty sure Nature is a dynamic enough system that it can manage to function pretty well without this particular variety of mosquito. I won\'t shed a tear, having been a walking banquet for mosquitoes my entire life. I hate them deeply.
There\'s only one species that could be eradicated with no effect whatsoever on the overall environment, a species that no other species relies on, that causes more deaths than mosquitoes and which the planet would sigh with relief with its guessed it.
Not sure whether eradicating ourselves is a more noble deed than doing so to any other species. Is it really a part of the discussion anyway? Would a mosquito push the button if it was given the chance to eradicate human beings? Only if it would be able to switch its diet to any other animal, I guess.. Then again, mosquitos don\'t have human brains, so the whole ethics discussion is a complexity only we are privileged to bring into the subject. Would we think/behave like animals, now that would be a different discussion. We would probably only kill to survive. In animal language: to feed or to PROTECT. Let the person throw the first stone who would gladly sacrifice his/her child for the sakes of human \"natural selection\". After all, who cares about the masses in Africa dying of these ugly diseases?.. I must agree with Mr Schacht here, who probably is the only person having a vote on the subject, if we talk about ETHICS. Yes, I think it is our MORAL obligation to protect ours. If you don\'t feel like being part of the survivors, there\'s always the choice: To be or Not to be! That being said, all the cutthroat environmentalists please keep to themselves before attacking yours truly with the allegation of being a destroyer of our planet: our foremost aim should be to protect and preserve, I fully support that. Harmony with our environment. With ALL of it. Or NONE of it. Otherwise we are just fooling ourselves by protecting the noble little stingers while killing the biggest mammals on earth by the masses. So let\'s just not have this little harmony idealism at the cost of having inferior species survive over ours: the human race has the POTENTIAL to create for the better and each individual should strive for just that. For the time being we do not exactly live up to our true potential, but why should we give up on our species already? We\'ve \"only\" been destroying the planet for about 150 years: if we fail in surviving this mess we got ourselves into, we simply got what we deserved! In case we wake up in time though, why should we help our eradication with the likes of the little stingy buggers? Might as well stand on top of the hill when the thunderstorm comes.. I would want my children to grow up safely, thank you. Without dengue fever lurking around the corner in our peaceful neighbourhood or in the Indo jungle for that matter. No, Africans and Asian don\'t exactly want to see their children dying either, a tipsy bit cruel to talk about millions dying as collateral damage. Anyway, it is indeed a hypocrit thing to do and so typically human to separate the mosquito matter from the rest of our \"survival deeds\": we could easily convince ourselves to eradicate mosquitos, for the simple reason that everyone hates them and they are proven to harm humans. Hmm, wasn\'t that the same that Spielberg tried to picture the shark?.. Until of course we found out it is a vital part of the foodchain, now we\'re back to protecting it. Shame the whale is not considered such by many, neither is the dolphin really being protected or the slaughter of millions of sharks being stopped and I could continue the list of endandered species. The hypocrism: it\'s easier to kill what we hardly see. Less of a mess. And who cares if in 100 years from now it turns out that mosquitos hold vital essences that could save mankind from total extinction by a newly mutated flu virus?..
great article
Ian Walker
So why not get the little buggers to inoculate against disease, make \'em little gene factories that help protect us against disease... Now that would be a true symbiotic relationship, and would signify real mastery of genetic engineering without eradicating another critter. Failing that, nuke \'em til they glow...