According to the latest study in the journal Nature, researchers from Imperial College London and the University of Washington, Seattle found that after making specific genetic changes to a few mosquitoes and then allowing them to breed could eventually dramatically reduce the spread of the deadly disease malaria.
This was the first successful ‘proof-of-principle’ experiment of its kind, they said, and suggests the method may in future be used to spread genetic changes in wild mosquito populations to make them less able to transmit malaria.
Andrea Crisanti of Imperial's life sciences department, who led the study said, “This is an exciting technological development, one which I hope will pave the way for solutions to many global health problems.” Malaria is an infectious disease that affects more than 240 million people every year, and kills around 850,000 annually - many of them children in Africa. But experts agree that the success of a genetic approach depends on getting the genetic modification to spread effectively in large mosquito populations.
For this experiment the researchers showed that a modified genetic element - a homing end nuclease gene called I-SceI - can efficiently spread through caged populations of mosquitoes. The genetic element 'homes' to a particular portion of the DNA, they explained, where it becomes integrated into the broken chromosome. This process - known as genetic drive - could be used to transmit a genetic change through a population of mosquitoes that affects the insects' ability to carry malaria.
The team bred mosquitoes with a green fluorescent gene as a marker that can easily be spotted in experiments. They allowed these insects to mate with a small number of mosquitoes that carried a segment of DNA coding for an enzyme which can permanently inactivate the fluorescent gene. After each generation, they counted how many still had a green gene. The results showed that after starting with almost 99 percent of fluorescent mosquitoes, more than half had lost their green genes in just 12 generations.
Of the nearly 3,500 species of mosquito in the world, only a few transmit the malaria parasite, Plasmodium falciparum. The researchers said this technique should allow scientists to focus on controlling just the most dangerous species.
Imperial's Nikolai Windbichler, who also worked on the study said, “In our mosquitoes the homing end nuclease gene is only passed on... directly to the carrier's offspring. This makes for a uniquely safe biological control measure that will not affect even very closely related mosquito species.”
As a next step the team is now working on targeting genes that the mosquito needs for reproduction or malaria transmission. With this technology, the release of a few modified mosquitoes could eventually cause a dramatic reduction in malaria-carrying mosquitoes in countries where the disease is endemic, they said.
Other academics have described the study as a “major step forward”. Professor Janet Hemingway, from the Liverpool School of Tropical Medicine, said the work was an “exciting breakthrough”. She cautioned that the technique was still some way off being used against wild mosquitoes and there were social issues around the acceptability of using GM technology. “This is however a major step forward providing technology that may be used in a cost effective format to drive beneficial genes through mosquito populations from relatively small releases,” she added. Dr Yeya Touré, from the World Health Organization, said, “This research finding is very important for driving a foreign gene in a mosquito population. However, given that it has been demonstrated in a laboratory cage model, there is the need to conduct further studies before it could be used as a genetic control strategy.”
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