Scientists make mosquitoes genetically infertile to stop spread of malaria

Researchers have found a way to drastically reduce malaria by genetically modifying mosquitoes to make them infertile. This would effectively eliminate an entire generation of the mosquito that spreads the disease.

This mosquito species, Anopheles gambiae, is one of the main vectors of malaria parasites in sub-Saharan Africa, where 90% of annual malaria deaths occur. Malaria caused 438,000 deaths and infected 214 million people worldwide in 2015, according to estimates from the World Health Organization.

In controlled experiments, the researchers genetically modified Anopheles gambiae so that females carried a modified recessive gene that disrupted egg production. The scientists used a technique called ‘gene drive’ to ensure the gene was passed down at an accelerated rate to more than 90% of offspring.

The spread could drastically reduce or eliminate local populations of the malaria-carrying mosquito species within a few years, according to the researchers’ article, which was published online December 7, 2015 in the journal Nature Biotechnology.

“The field has been trying to tackle malaria for more than 100 years,” said co-author Andrea Crisanti, PhD, Professor of Molecular Parasitology at Imperial College London, in London, UK. “If successful, this technology has the potential to substantially reduce the transmission of malaria.”

To test the gene drive technique in Anopheles gambiae mosquitoes, the team first identified three female fertility genes. The researchers then modified these genes with CRISPR/Cas9 endonuclease, a type of DNA “cutting tool” that can be designed to target and disrupt very specific parts of the genetic sequence.

When chromosomes carrying these modified genes encountered chromosomes without the gene variant, the CRISPR/Cas9 endonuclease cut a sequence in the normal gene, causing a break. The broken chromosome used the chromosome carrying the genetic variant as a template to repair itself, and copied in the code with the altered gene variant.

When the researchers checked the progress of the gene drive technique, 91.4% to 98.6% of the mosquitoes’ offspring carried genetic code for infertility. The researchers also observed that the modified mosquitoes produced a fraction of larvae that normal mosquitoes would.

The team now aims to improve the expression of their gene drive elements and also to find more genes to target, in order to reduce the possibility that the mosquitoes develop 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 first author Andrew Hammond, PhD, a researcher in Dr. Crisanti’s lab.