Anopheles gambiae
Anopheles gambiae, a species of mosquito that carries the malaria parasiteJames Gathany/CC

A species of mosquito known to be a major carrier of dangerous malaria parasites has been genetically modified to become infertile. Scientists say the modification of the genes of Anopheles gambiae could lead to the drastic reduction – or even the elimination – of local populations, thereby reducing the spread of disease.

Anopheles gambiae is found in sub-Saharan Africa, where 90% of malaria deaths occur. The team, from Imperial College London, said the technique (called 'gene drive') could be used in conjunction with other interventions to stop the spread of the disease.

Publishing their findings in the journal Nature Biotechnology, the team modified the mosquito genes to disrupt egg production in female insects. They identified three genes that impacted female fertility and then modified these with a DNA-cutting tool that allows them to target very specific parts of the genetic code.

Impact on the ecosystem?

Globally, there are around 3,400 species of mosquito. Anopheles gambiae is one of 800 found in Africa. For this reason, suppressing the species in certain areas should not significantly impact local ecosystems, lead author Tony Nolan said.

They were also able to use the gene drive technology to ensure the modified genes were passed on rapidly so it would spread through the population at an accelerated rate. Under normal circumstances, each gene has a 50% chance of being passed down to offspring. However, the scientists were able to make it so the infertility genes were passed on 90% of the time.

This was done through recessive genes. Many mosquitoes would only carry one copy of the gene (these are carriers, used to spread the gene) – but two are needed to cause infertility. When chromosomes carrying the modified genes come into contact with the normal genes, it causes the latter to break. The broken chromosome then uses the modified version as a template to repair itself, copying the infertility code in the process. "These findings could expedite the development of gene drives to suppress mosquito populations to levels that do not support malaria transmission," the scientists wrote.

Researchers said the gene drive technology has the potential to modify mosquito populations in just a few years. However, they said it will be a decade before it could be introduced as a "working intervention". Nevertheless, scientists are hopeful of future applications. Study co-author Andrea Crisanti said: "The field has been trying to tackle malaria for more than 100 years. If successful, this technology has the potential to substantially reduce the transmission of malaria."

They also said they will now be looking to improve the expression of the gene drive and to find more genes to target. This would reduce the possibility of mosquitoes developing resistance to the modification. "We hope others will use our technique to understand how mosquitoes work, giving us more ammunition in the fight against malaria," said author Andrew Hammond.

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