PHA-Exchange> Scientists plan to wipe out malaria with GM mosquitoes

[Claudio Schuftan]

> Scientists plan to wipe out malaria with GM mosquitoes
> ------------------------------------------------------
> James Meek, Science correspondent 
> Monday September 3, 2001 
> The Guardian 
> 
> Scientists fighting malaria are preparing the ground for one of the 
> most audacious attempts ever to wipe out disease: genetically modify-
> ing an entire animal species in the wild. 
> 
> In laboratories around the world, there is increasing confidence that 
> scientists will acquire the ability to spread a synthetic gene 
> throughout the populations of dangerous mosquitoes, making it impos-
> sible for them to pass malaria on to humans. 
> 
> Until now, spreading genes throughout a species was something only 
> evolution was capable of, over millions of years of natural selec-
> tion. But scientists think it might be possible to transform the ma-
> laria-carrying mosquito into a subtly different species - still a 
> bloodsucking nuisance, but no longer a killer - within two to 25 
> years of releasing the first GM insects. 
> 
> In a sign of how fast research is moving, specialists in the field 
> are gathering in London next week for a conference to discuss the 
> risks and benefits of releasing GM mosquitoes into the wild. 
> 
> "We're not talking about one to one replacement of lab mosquitoes for 
> wild mosquitoes," said Tony James, of the University of California in 
> Irvine, who is attending the conference at Imperial College. "There's 
> no question of competition between transgenic and non-transgenic in-
> sects. What we're talking about is actually driving the gene through 
> a population. It's an ambitious idea." 
> 
> In the lab, Dr James's team has already inserted a gene into mosqui-
> toes which makes it impossible for the parasite that causes malaria 
> to gain a foothold. 
> 
> Last year, a joint British-German team, partly led by one of the or-
> ganisers of next week's conference, Andrea Crisanti of Imperial Col-
> lege, created a transgenic mosquito - a GM mosquito whose offspring 
> would also carry the inserted gene. 
> 
> "For the past decade, our efforts have been rather esoteric, trying 
> to get to a certain stage. We are at that stage now," said Dr James. 
> "We're able to put genes into animals in a stable way." 
> 
> But there are concerns. Luke Alphey, a specialist in the field at Ox-
> ford University, supports the release of GM insects into the wild to 
> combat disease. But he is wary of the idea of genetically modifying 
> an entire species. "I have a rather negative view of this strategy," 
> he said. "One of my con cerns is that once you've let such a thing 
> go, you can never recall it." 
> 
> Supporters of the approach point out that it is not necessary to mod-
> ify every single dangerous mosquito to stop the disease. But the na-
> ture of the technique is such that this could well be the end result. 
> 
> Normally, a new gene will spread to cover an entire species only if 
> it gives animals who have it some survival or reproductive advantage 
> over animals that do not. But scientists have found two ingenious 
> ways to drive a non-advantageous gene through mosquito populations so 
> that eventually all mosquitoes inherit it. 
> 
> One is to attach the gene to a bacterium called wolbachia, which can 
> be made to infect mosquitoes, becoming effectively a part of the in-
> sect. When GM females mate with males, they produce GM offspring, 
> whether the males are GM or not. But because of the peculiar proper-
> ties of wolbachia, non-GM females cannot have offspring with GM 
> males. In other words, GM females will always have more children, 
> eventually crowding out their non-GM rivals completely. 
> 
> Freakish
> 
> The other method attaches the gene to a freakish chunk of DNA called 
> a transposable element, which hops between chromosomes during repro-
> duction. 
> 
> Normally, mating between parents with different genes gives the off-
> spring a 50% chance of inheriting either gene. Because of the trans-
> posable elements moving around, however, the GM mosquito will always 
> pass on the added gene to more than 50%of its offspring - again, 
> eventually covering an entire species. 
> 
> Sixty of the 380 mosquito species can transmit malaria, although one, 
> Anopheles gambiae, is responsible for a large part of the 2.7m deaths 
> caused by the disease each year. In order to transform a single spe-
> cies, GM insects would have to be released in many locations to 
> spread the gene through different populations of that species. 
> 
> Steven Sinkins, of the Liverpool School of Tropical Medicine, who has 
> done extensive research into mosquitoes and wolbachia, said tests of 
> a complete system were unlikely in the next two years, but progress 
> had been rapid. 
> 
> "From the theoretical point of view, there's no reason why either ap-
> proach should not be successful," he said. 
> 
> Malaria is transmitted by female mosquitoes who harbour a parasite 
> called plasmodium. The parasite infects humans from the insect's sa-
> liva when it drinks the person's blood. The World Health Organisation 
> estimates that there are 500m cases of malaria each year, with plas-
> modium becoming resistant to drugs and mosquitoes becoming resistant 
> to insecticides. 
> 
> Dr Sinkins argued against the idea that human intervention in a wild 
> species on such a scale was unnatural or wrong. The species would 
> live on: it would just be more human-friendly. 
> 
> "It doesn't have to be anything too unnatural," he said. "Within a 
> mosquito population there will always be some with a natural inabil-
> ity to transmit the parasite. All you're doing is increasing the per-
> centage of individuals with those genes. They'll still be biting." 
> 
> Dr James said the genetic approach was no more unnatural than the 
> massive, failing effort of drugs and insecticides. 
> 
> "The last thing anybody wants to be known for is irrevocably screwing 
> up mankind or the environment. The whole idea is to figure out how 
> one conducts experiments, what's going to be safe, and what's not. 
> 
> "The problem of infectious disease is going to be an eternal strug-
> gle. What we are looking for is the next wave of useful tools that's 
> going to buy us time." 
> 
Courtesy of Dr Brian Pazvakavambwa, MBChB, MPH 
> World Health Organization (Geneva)