AFRO-NETS> Scientists plan to wipe out malaria with GM mosquitoes

[Dr Brian Pazvakavambwa <pazvakavambwab@who.ch>]

Scientists plan to wipe out malaria with GM mosquitoes
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Special report: the ethics of genetics 

James Meek, Science correspondent 
Monday September 3, 2001 
The Guardian 

http://www.guardian.co.uk/international/story/0,3604,546050,00.html

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." 

---
Dr Brian Pazvakavambwa, MBChB, MPH 
Department of HIV/AIDS 
World Health Organization (Geneva) 
mailto:pazvakavambwab@who.int 
http://www.who.int/HIV_AIDS/ 
http://www.bpazva.8m.com

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