A new study brings closer the day when mosquitoes lose their ability to transmit malaria – a disease that kills hundreds of thousands of people a year, many of them young children and pregnant women in Africa.
Image credit: CDC/Jim Gathany
Scientists from the University of California (UC) have created a strain of mosquito that is capable of rapidly spreading malaria-resistant genes into a mosquito population through its offspring.
They used a powerful new gene-editing tool called CRISPR to insert anti-malaria antibody genes in a targeted DNA site of mosquito embryos.
The researchers believe the achievement marks a significant step toward being able to create a malaria-resistant mosquito population in an effort to wipe out the disease.
The team, comprising members from UC’s Irvine and San Diego campuses, describes the work in the Proceedings of the National Academy of Sciences.
About half of the world’s population is at risk of malaria, a disease caused by parasites that are transmitted to people through the bites of infected mosquitoes.
According to World Health Organization (WHO) estimates, during 2015, around 214 million people will have been infected with malaria and 438,000 will have died of it – more than two thirds of the deaths occurring among African children under the age of 5.
In their study, the UC team worked on a mosquito called Anopheles stephensi, the main carrier of malaria in Asia.
Using CRISPR, they inserted a DNA element into the germ line of the mosquito and showed it stopped 99.5% of offspring being able to pass on malaria.
Anthony James, a professor at UC-Irvine whose lab has been engineering anti-disease mosquitoes for nearly 20 years, says:
“This opens up the real promise that this technique can be adapted for eliminating malaria.”
Previous work involving the James lab had shown that introducing antibodies from the immune system of mice into mosquitoes could disrupt the malaria parasite’s biology. But this trait could only be passed on to half the offspring – because it only affected one of the two copies of the relevant gene.
Meanwhile, at UC-San Diego, some of the study authors working on fruit flies found that using CRISPR they could insert modifications in both copies of a gene.
The two groups came together to work on the new study. They created a genetic “cassette” comprising the antimalaria genes and a DNA cutting tool that, when injected into the mosquito embryo, targeted a specific location in the germ line DNA to insert the genes.
To check that the malaria antibody genes had reached the right destination in the mosquito DNA, the researchers inserted an extra gene that makes the offspring’s eyes glow red.
They found that 99.5% of the offspring had red fluorescent eyes – an “amazing result,” says Prof. James.
There is still a long way to go before such a method can be tested in the field. There are technical hurdles – such as confirming that the antibodies actually work against the malaria parasite – and also regulatory hurdles – such as the challenges of getting permission in several countries to test modified mosquitoes that do not recognize national borders.
But Prof. James is optimistic. “This is a significant first step,” he notes, and adds:
“We know the gene works. The mosquitoes we created are not the final brand, but we know this technology allows us to efficiently create large populations.”
Research to tackle malaria is progressing on a number of fronts. For example, another study that Medical News Today learned of recently shows how a protein important for cell division drives the growth of the malaria parasite in mosquitoes. The researchers believe the discovery could be important for developing treatments to stop the disease.