Scientists have managed to eradicate a large population of malaria-transmitting insects using genetic engineering. This radical method renders females infertile and is the most advanced use of this technology in fighting the disease.
The study not only brings new hope to the fight against this killer, but it also lays the foundations of further testing of gene-drive technology. This could lead to self-destructing mosquitoes being released into nature within 10 years.
This is an exciting development, according to Dr Thomas Price, a senior lecturer at the University of Liverpool in evolution, ecology, and behaviour. He was not involved with the research. There are many ethical and regulatory questions to be answered. If it is not possible to create gene drives that work in the field, none of these matters. This is an important step towards that goal.
Despite recent improvements in malaria control, there were still 229m cases and 409,000 deaths in 2019.
Dr Drew Hammond from Imperial College London led the research. He said that gene drive is a self-sustaining, fast acting technology that can be used alongside existing tools like bed nets, insecicides and vaccines. It could prove to be a major breakthrough in the fight against malaria.
This development seeks to bypass natural selection by inserting a set genetic instructions that will quickly spread through a population, passing on a specific trait in this instance infertility much faster than can be achieved through traditional selective breeding.
In 2003, the idea was first proposed. However, scientists found that after several generations their gene drives vanished due to mutations that stopped them from spreading further. Hammond and his team refused to give up. They began looking for a better place to insert their gene drives.
Certain areas of DNA are extremely conserved. This means that any mutation will likely to cause serious damage to their owners. These areas can be chosen to allow gene drives to last longer.
Scientists discovered a critical sex determination gene called "doublesex" that is identical to all Anopheles.gambiae mosquitoes. This species is responsible for the majority of malaria transmission in sub-Saharan Africa. The gene drive in this gene prevents female mosquitoes from producing offspring.
Hammonds used doublesex to kill 600 A gambiae mosquitoes in a small enclosure. In seven to eleven generations, no more offspring were created.
Field trials were also launched in Burkina Faso that same year by the Target Malaria Research Consortium, which includes the Imperial Team. To test their ability to survive in the wild, genetically modified male mosquitoes were released into the wild. This was an important step towards field trials of gene drive organisms.
This new research, published by Nature Communications, is yet another step towards that goal. Hammond and his collaborators tested whether the same gene-drive they tried in 2018 would spread to cause the same population collapse under real-world conditions. The World Health Organization has recognized the importance of such testing before gene drive technology can be used in the wild.
Researchers released a small number of modified mosquitoes into larger indoor cages that house hundreds of wild-type, older mosquitoes at a research center near Siena in central Italy. The cages were created to attract the mosquitoes to complex mating, resting and egg-laying behaviors that are impossible in small cages.
Researchers tracked the speed at which the gene drive spread and examined its effect on fertility and population decline.
This feat is unprecedented. A single gene drive was released into a simulation field population. It caused a collapse of the entire population in a year. There was no human input. Hammond, who also works at the Johns Hopkins Malaria Research Institute in Baltimore, stated that it is self-sustaining.
Hammond stressed however that larger field trials would require more thorough gene drive testing and environmental risks assessments. This could include the release of genetically modified non-sterile mosquitoes in order to determine if they will mate with wild ones and if so, to what extent.
These field trials could begin within the next few year. Hammond stated that if they succeed, he can imagine that we will have a small release of gene-drive mosquitoes within 10 years at our field testing site in Burkina Faso.