It’s been over a decade since scientists created a mosquito genetically modified so its ability to transmit malaria—which kills 750,000 people each year worldwide, mostly in Africa—was virtually eliminated. But so far the anti-malarial GM mosquitoes have not been introduced into the wild, because the modification carries no definite survival advantage and would likely simply fade out of the wild population over time.
That may have just changed.
The eukaryotic protist Plasmodium that causes malaria has proven fiendishly adept at evolving resistance to drug after drug designed to prevent the sickness in humans. Even Lariam (mefloquine hydrochloride), the potent prophylactic known to cause rare but serious neuropsychiatric side effects (not to mention cardiac arrhythmia), is showing signs of reduced efficacy. Of course if one minimizes getting bitten by mosquitoes in the first place the risks of contracting the disease go down. But while avoidance strategies such as bed nets, protective clothing, and insect repellent help, they are not 100 percent effective, nor are they often available to poor people in malarial regions. Residential application of pesticide has been shown to be effective, and there is a campaign to re-approve DDT for this purpose, as its risks in small amounts are far lower than the risk from malaria (the huge environmental problems caused by DDT in the 1950s and 1960s resulted from mass aerial sprayings over farmland, not residential use). But, again, pesticides cannot eliminate the possibility of being bitten.
What if we could skip drugs, bed nets, and pesticides altogether and create a mosquito that was incapable of transmitting malaria?
That was accomplished in 2000 at Imperial College London. But being unable to transmit malaria has a neutral effect on the mosquito—it adds no survival advantage except in a few rare situations, so if such a population were released into the wild, the modified gene would probably disappear over time.
Now scientists at ICL have figured out a way to make the modification spread through a wild population, using something called a homing endonuclease gene, which can make a copy of itself, ensuring that all offspring wind up with a copy as well. When the researchers introduced the HEG into one percent of a sample mosquito population, they found that in just 12 generations (each generation requires about 20 days), the gene had spread through half the population.
So—we’re not leaving the Off! home just yet, but we’ll follow these developments with interest.
Link to the article on SciDev.net:
http://www.scidev.net/en/news/survival-prospects-boosted-for-antimalarial-mosquitoes-.html
And, if you really want the full story, the report in Nature:
http://www.nature.com/nature/journal/v473/n7346/full/nature09937.html