Genetic modification raises hope that malaria-transmitting mosquitoes may one day be eradicated, research suggests.
Scientists from Imperial College London used a gene-editing technique called Crispr, which acts like scissors to "cut" certain pieces of the insects' DNA.
Focusing on the malaria-spreading species Anopheles gambiae, the team targeted a gene that is vital for the female insect's reproduction.
Within one year, the altered gene had "fully suppressed" the study's mosquito population, in a move one scientist has called a "game-changer in bringing about malaria elimination".
Around 229 million malaria cases are thought to have occurred worldwide in 2019 alone, killing 409,000 people.
Nearly half of the world's population are vulnerable to malaria, however, almost all (94%) cases and deaths occur in Africa.
An insecticide-impregnated mosquito net can ward off the disease. In 2019, nearly half (46%) of at-risk people were protected by a net, up from just 2% in 2000. Coverage is said to have been at a standstill since 2016, however.
Insecticide resistance is also an issue, with mosquitoes said to have developed resistance to at least one in four commonly-used classes of the sprays.
There is just one anti-malaria vaccine, which reduces the risk of severe disease among young children in Africa. It only acts against the species Plasmodium falciparum, the most deadly malaria parasite worldwide and the most prevalent across Africa.
In sub-Saharan Africa specifically, A. gambiae is said to be behind most of the malarial transmission.
In both male and female mosquitoes, the Imperial scientists targeted a gene called "doublesex".
Carriers of the edited gene were not infertile themselves, however, when two copies of the modified DNA are passed down from both parents, the female offspring becomes "intersex".
This is defined as displaying "female-male sexual development", leaving the mosquito unable to produce offspring.
Once the mosquitoes were genetically-modified to become carriers, they were free to breed with wild insects in large indoor cages that "partially mimic natural conditions".
Within one year, the modified gene had "spread rapidly, fully suppressing the population", as reported in the journal Nature Communications.
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The scientists hope the genetic modification will be used alongside other methods of warding off malaria, like bed nets and insecticides.
Although the research is in its infancy, the results are a "major step towards" genetically-modified mosquitoes being released into the wild, possibly within 10 years, according to Dr Thomas Price, from the University of Liverpool.
There are still roadblocks, however, with these genetic-modifications previously vanishing within a few generations due to the emergence of mutations that stop their spread.
In 2018, however, the Imperial scientists targeted the doublesex gene in around 600 A. gambiae mosquitoes that were housed in a small cage, which less accurately mimics real-world conditions. Nevertheless, offspring reportedly stopped being produced within seven to 11 generations.
In the latest study, "a single release" of the genetically-modified mosquitoes "brought about a crash of that entire population within a year", in a move that was "entirely self-sustaining", according to study author Dr Andrew Hammond.
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