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Genetically engineered mosquitoes pass lethal gene to offspring

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  • Scientists carry out ‘positive’ trial on Cayman Islands
  • New breed of insect could be used to tackle malaria and dengue fever
  • But critics say it could lead to public health problems

Breakthrough or danger? A UK-based research team has found a way of genetically modifying the Aedes aegypti mosquito so they pass on a deadly gene to their offspring

Breakthrough or danger? A UK-based research team has found a way of genetically modifying the Aedes aegypti mosquito so they pass on a deadly gene to their offspring

Serious concerns have been raised over the release of a new breed of disease-fighting mosquito which has been genetically engineered to kill their own offspring.

There are hopes the project could be used to control agricultural pests and tackle deadly insect-borne illnesses such as dengue fever and malaria.

But the research has raised concerns about the possible side-effects on public health and the environment because, once released, the mosquitos cannot be recalled.

A UK-based scientific team revealed there had been positive signs from the first release into the environment of the mosquitoes, which are engineered to pass a lethal gene onto their offspring, killing them before adulthood.

The study team – which includes experts from Imperial College London and the Liverpool School of Tropical Medicine – released batches of modified mosquitoes in an area of the Cayman Islands where the dengue virus-carrying Aedes aegypti mosquito is common.

The study, published in Nature Biotechnology journal, looked at how successfully the lab-reared, genetically modified insects could mate.

About 19,000 mosquitoes engineered in a lab were released over four weeks in 2009 in a 25-acre area on Grand Cayman island.

Based on data from traps, the genetically engineered males accounted for 16per cent of the overall male population in the test zone, and the lethal gene was found in almost 10 percent of larvae.

Those figures suggest the genetically engineered males were about half as successful in mating as wild ones, a rate sufficient to suppress the population.

Disease fighter? The new breed of mosquitoes could be used to tackle killer illnesses like dengue fever and malaria which affect the world's poorest populations

Disease fighter?  The new breed of mosquitoes could be used to tackle killer illnesses like dengue fever and malaria which affect the world’s poorest populations

Luke Alphey, chief scientific officer at Oxitec, the firm which devised the technique, told the BBC: ‘We were really surprised how well they did.

‘For this method, you just need to get a reasonable proportion of the females to mate with GM males – you’ll never get the males as competitive as the wild ones, but they don’t have to be, they just have to be reasonably good.’

HOW MOSQUITOES KILL THEIR OWN CHILDREN

  • The genetic approach used to create the mosquitoes is a system known as tetracycline-controlled transcriptional activation (tTA).
  • The technique is an extension of one successfully used for decades to control or eradicate pests which involves sterilising millions of insects with radiation.
  • But the process has not worked with mosquitoes, partly because the radiation also injures them, making it difficult for them to compete with healthy counterparts for mates.
  • So Oxitec has now created the Aedes aegypti mosquitoes with a gene that will kill them unless they are given the common antibiotic tetracycline.
  • With tetracycline provided in the lab, the mosquitoes can be bred for generations and multiplied.
  • Males are then released into the wild, where tetracycline is not available.
  • They live long enough to mate but their progeny will die before adulthood.

 

Authorities in the Florida Keys hope to carry out an open-air test on the modified insects as early as December after experiencing the region’s first cases of dengue fever in decades.

Dr Alphey said the technique was safe because only males were released as it was only the females that bite people and spread the disease.

But critics say the process is by no means foolproof.

Alfred Handler, a geneticist at the Agriculture Department in Gainesville, Florida, said the mosquitoes can evolve resistance to the lethal gene while being bred for generations in a lab.

Todd Shelly, an entomologist for the Agriculture Department in Hawaii, also said in a commentary published on Sunday by Nature Biotechnology that 3.5per cent of the insects in a lab test survived to adulthood despite presumably carrying the lethal gene.

Also, the sorting of male and female mosquitoes, which is done by hand, can result in up to 0.5per cent of the released insects being female, the commentary said.

If millions of mosquitoes were released, even that small percentage of females could lead to a temporary increase in disease spread, it was reported by the New York Times.

Oxitec and a molecular biologist, Anthony A. James of the University of California, Irvine, say they have developed a solution — a genetic modification that makes female mosquitoes, but not males, unable to fly.

The grounded females cannot mate or bite people, and separating males from females before release would be easier.

The World Health Organisation expects to release guidance on how GM insects should be deployed in developing countries by the end of the year.

 

Via DailyMail

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Should we let scientists release mutant mosquitoes into the wild to try to wipe out malaria?

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Malaria is one of the world’s last great scourges. It affects more than 200 million people and kills almost a million African children each year.

With other great killers such as smallpox and measles banished or in full retreat, malaria is surely ripe for elimination.

But malaria is a resourceful enemy, spread by certain types of mosquito that carry a parasite that harbours the disease. The mosquitoes pass on the parasite in their bite.

Pesticides haven’t killed off malaria and the drugs we are told to take when we fly to malarial zones don’t always work.

Now scientists say they have invented a way of stopping malarial mosquitoes in their tracks. They say it could rid the world of the disease in just a few years.

‘That’s why it’s so exciting,’ says the biologist behind the breakthrough, Andrea Crisanti of Imperial College London.

The trick is a nifty bit of genetic engineering that might cause those opposed to ‘Frankenstein’ technology to think again – or maybe not.

It is ten years since scientists announced that they could change the genes of mosquitoes so that they did not pass on the malaria parasite. But that was in the lab.

The problem is you can’t bring all the world’s mosquitoes into the lab for a genetic refit.

And however many of the mutants you release into the wild, their new genetic trait will most likely die out within a few generations.

So the scientists decided they needed to up the odds that the offspring of the mutant mosquitoes would inherit and pass on the genetic modification. This is what they think they have now achieved.

They have done it by adding a second ‘super-gene’ that dramatically increases the male mosquito’s ability to spread the anti-malarial gene.

They found the super-gene in fungi and successfully transplanted it into Anopheles gambiae, the set of species of mosquito that causes three-quarters of all malaria deaths.

The super-gene is sometimes called a selfish gene because it ensures that all the sperm produced by genetically modified mosquitoes carry the same trait. And that is enough to give this genetic trait a huge advantage when it comes to the survival of the fittest.

‘In the lab, the mutation spread to more than half the population within 16 generations – less than a year,’ says Crisanti.

Now he is thinking big. Re-engineer a few thousand male malarial mosquitoes, release them into the wild and watch them and their sperm take over the mosquito world.

Now that the genetic transport mechanism is sorted out, the big question is exactly what genetic traits the new mutant mosquitoes should pass on. How best to kill off malaria?

There are three possible lines of attack, says Crisanti.

The first is to stop the mosquito excreting the parasite when it bites.

The second is to destroy the genes that mosquitoes use to recognise humans to bite.

This seems to be to do with smell (mosquitoes love cheesy feet – I once went to an insect lab in Kenya, one of the world’s malarial hotspots, where volunteers with smelly feet camped out in the name of science to see who would be bitten most).

Crisanti says he knows how to snip out the gene that allows mosquitoes to sniff us out. After that, he says, they will bite animals instead.

The third option is to screw up their reproductive systems so that they produce only males.

Not surprisingly, if you set that gene rolling, after a few generations the entire population crashes. Again, he says, the gene engineers know how to do that.

So problem solved. Buzz off malaria.

Well, sure. Except that nobody is quite sure what the wider effects of messing with the genes of mozzies might be.

Re-engineering trillions of insects that spend their lives going round biting other members of the animal kingdom might risk spreading genetic mayhem.

Ingeborg van Schayk, director of the Malaria Foundation, whose membership comprises more than 6,000 medics and others fighting malaria, says: ‘We do not support the release of GM mosquitoes as long as the long-term effects on people and their environment remain uncertain… We don’t know if malaria mosquitoes will adapt to being “modified” and leave us with even bigger problems.’

Janet Hemingway, an insect specialist at the University of Liverpool, says that GM mosquitoes are unlikely to develop Frankenstein tendencies such as spreading other diseases or expanding their terrain to invade the streets of Britain.

‘There is no logical reason why they would,’ she says.

‘And it is almost inconceivable that they would suddenly start to vector other diseases.’

She is concerned that the malaria parasite itself might evolve to find another route to reach us.

‘But that is difficult to predict in advance. We will probably only find out when the big eradication push is well under way,’ she says.

What if the GM mosquitoes passed on their mutant genes to other species, either animals that they bite or animals that eat mosquitoes?

Crisanti believes the chances of that happening are ‘near zero’. But to check he is building a mosquito lab in his native Italy, where he will incarcerate thousands of GM mosquitoes for three years in a near-natural environment.

If all goes well, he could be doing big field trials in the African bush within three years.

So is the risk worth taking? Should we be bold, whatever our fears?

Some people say we are still stuck with the malaria problem today only because we were squeamish once before.

Back in the Sixties, it looked as if the world was about to eradicate malaria using a pesticide that was amazingly effective at killing mosquitoes. That pesticide was DDT.

The U.S. government set aside half-a-billion dollars, and thousands of drums of DDT headed to the developing world for spraying on hut walls, where malarial mosquitoes gather at night after biting their human hosts.

Malaria deaths fell by as much as 95 per cent at the height of the spraying. The end seemed near.

But then came Rachel Carson’s famous book Silent Spring, which described the horrific damage DDT and other new farm chemicals caused to wildlife.

Carson called for a ban only on spraying DDT in fields, not in houses to kill mosquitoes.

Even so, the world got cold feet, DDT was largely withdrawn and malaria made a comeback.

Only in 2006, did the World Health Organisation again back DDT as one of its main weapons against malaria.

Many scientists today fear we may repeat the mistake – by letting our concerns about genetic modification get the better of our desire to banish malaria.

‘I am not saying using GM mosquitoes is without any risk,’ says Crisanti.

‘I am as concerned about environmental safety as anyone. But, meanwhile, a million children continue to die every year from malaria.’

If he gets the go-ahead, Crisanti reckons it may not take much more than a couple of years to wipe out malaria once and for all.

Do we in the malaria-free world have the moral right to try to stop him?

It’s not our kids that are dying. Not many of us have direct experience of this dreadful disease.

So it would be interesting to know what Cheryl thinks.

Via DailyMail