In a study published yesterday in Nature Biotechnology, researchers were able to completely block reproduction in laboratory mosquitos. The technique they used, called gene drive, was used to selectively target Anopheles gambiae, the specific mosquito species that is responsible for malaria transmission in sub-Saharan Africa.
"It will still be at least 5–10 years before we consider testing any mosquitoes with gene drive in the wild, but now we have some encouraging proof that we're on the right path,” lead researcher Andrea Crisanti from Imperial College London says. “Gene drive solutions have the potential one day to expedite malaria eradication by overcoming the barriers of logistics in resource-poor countries."
In 2016, there were around 216 million malaria cases and an estimated 445,000 deaths worldwide, mostly of children under five years old.
The team targeted a gene in Anopheles gambiae called doublesex, which determines whether an individual mosquito develops as a male or female. Males who carried this modified gene showed no changes, and neither did females with only one copy. However, females with two copies showed both male and female characteristics, failed to bite, and did not lay eggs. After eight generations, no females were produced, and the populations collapsed because of lack of offspring.
Previous attempts to develop gene drive for population suppression have encountered resistance, due to target genes developing mutations that stop the gene drive. One of the reasons doublesex was picked for the target in this study is that it is thought to not tolerate any mutations. Indeed, in the study, no functional mutated copy of the doublesex gene arose and spread in the population.
According to the team, additional experiments are needed to investigate the efficacy of the gene drive under conditions that mimic tropical environments. This involves testing the technology on larger populations of mosquitoes that are confined in more realistic settings, where competition for food and other ecological factors may change the fate of the gene drive. Fortunately, recent work from Imperial showed that suppressing Anopheles gambiae populations in local areas is unlikely to affect the local ecosystem.
The Doublesex gene is similar across the insect world, suggesting that this technology could be used in the future to specifically target other disease-carrying insects.