Genetically modified (GM) mosquitoes could soon be released into the wild in an attempt to combat malaria. Scientists at Imperial College London, who created the GM insects, say they could wipe out natural mosquito populations and save thousands of lives in malaria-stricken regions.
Led by Andrea Crisanti, the team added a gene that makes the testicles of the male mosquitoes fluorescent, allowing the scientists to distinguish and easily separate them from females. The plan is to breed, sterilize and release millions of these male insects so they mate with wild females but produce no offspring, eradicating insects in the target region within weeks.
Specific
Crisanti said: "Our mosquitoes are nearly ready for testing in the wild. This is a technology that works and could make a real difference. The beauty is that it's very specific. Unlike insecticides, sterile males target only the species you want to attack."
Mosquitoes that spread malaria have long been a target for sterile-male technology, which has been used to eradicate the screwworm fly from the US, Mexico and Central America.
The International Atomic Energy Agency has been using its radiation technology to support health projects, and wants to release sterile mosquitoes to tackle malaria in northern Sudan and on Reunion island in the Indian Ocean -- but they and other groups have been hampered by an inability to distinguish the males, which do not bite people. Female mosquitoes transmit malaria, even if sterile, so releasing them alongside males would make the situation worse.
Crisanti said: "The really challenging problem is to identify the males. There is no difference between the larvae and as adults they fly, so the logistics of trying to separate them when they're adults is immense."
* The world's most common and deadly parasitic disease
* It is spread from person to person when female mosquitoes feed on human blood
* Infects up to 500 million people each year
* Kills an estimated 2.7 million people annually
* Male mosquitoes can be sterilised using chemicals and radiation
* If enough sterile males can be released to breed with females, the insect population of a target region can crash within weeks
Source: The Observer
To solve the problem, his team altered the DNA of the mosquito species Anopheles stephensi, the principal carrier of malaria in Asia, so that the males expressed a fluorescent green protein in their sperm.
A sorting machine based on laser light separated male from female larvae, according to whether they glowed or not. Writing in Nature Biotechnology yesterday, the scientists say the machine could sort up to 180,000 larvae in 10 hours.
The next step is to scale up the technique to provide the millions of GM insects needed to make a large-scale release effective. The scientists also need to check whether the sterile males will be strong enough to compete with wild rivals when released -- the strategy depends on female mosquitoes, who only mate once in their two-week lifespan, choosing sterile males.
Crisanti said other mosquito species could be modified in the same way, including Anopheles gambiae, which is responsible for a large part of the 2.7 million deaths caused by malaria each year. He is talking to international agencies about setting up a trial.
Scientists have previously considered releasing both male and female mosquitoes that have been genetically modified in a different way, making them unable to transmit malaria.
The idea is that altered insects would spread the disruptive genes through natural mosquito populations, but concerns about whether the inserted genes could transfer to other organisms have so far scuppered plans to set up large-scale breeding colonies to test it.
Low risk
Crisanti said that, because the new GM mosquitoes are sterilized, releasing them into the environment does not pose significant risks: "It won't transmit any genes to the environment."
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