That’s why several research groups are working on genetic modifications to mosquitoes that would prevent them from spreading the parasite. The latest advance comes from the University of California, Irvine, which has created a mosquito that not only doesn’t transmit malaria but also passes on this trait to 99.5 percent of its offspring.
That’s quite an achievement, since many traits inherited in a more typical fashion go to only a fraction of an organism’s offspring, says researcher Anthony James. His team used a gene-editing technique called CRISPR to insert two genes into the insect’s genome to confer malarial resistance. Given the high rate of inheritability, the resistance would theoretically spread quickly throughout a population once it has been introduced, James says.
The UC Irvine team worked on the genome of Anopheles stephensi mosquitoes, which are a main vector of malaria in India, where there are more than 1 million cases annually and more than 500 deaths. There’s reason to believe the technique would work in other species as well, according to a study describing the finding, published November 23 in the journal Proceedings of the National Academy of Sciences. David O’Brochta, a researcher at the University of Maryland who wasn’t involved in the study, says “this kind of system could help defeat malaria.”
In the past couple of years, CRISPR has changed the way much genetic modification is done. It works by allowing scientists to cut DNA at a specific location in the genome, and to insert desired genes. Compared with previous methods, it is much quicker and cheaper. This technique of introducing malaria resistance used by the UC Irvine team was, for example, first demonstrated in fruit flies earlier this year; just a few months later, the team successfully applied the same method to mosquitos. Older gene-editing techniques would have taken much longer to fine-tune for different animals.
The two genes James’s team has introduced are modified mouse immune genes, which bind to the malaria parasites and prevent them from recognizing their host and moving around in the mosquito’s body. “You can think of it as [being] blinded,” James says. As a result, the parasite cannot get into the animal’s salivary gland and, therefore, doesn’t make it into humans when the mosquitoes bite.
James says the innovation needs to be tweaked slightly before being applied in the field, and introducing genetically modified organisms into the wild would require regulatory approval from foreign countries where malaria is endemic. But he’s hopeful it could be introduced sometime in the next several years.
In the short time it has been in use, CRISPR has raised a number of ethical questions. In April, scientists used the technique to modify human embryos; the team attempted to avoid ruffling feathers by using nonviable embryos, but the experiment created a firestorm of controversy anyway. James says more research needs to be done on likely long-term effects of the modification before using it in the real world. There is some concern, for example, about what might happen if the “gene drive”—the genetic mechanism that causes the trait to be passed on to nearly all offspring—were to make its way into another organism, O’Brochta says; perhaps an undesirable gene might spread through a whole population of animals, wiping out a species. But this seems unlikely, James says, and at this point the potential benefits of helping to stop malaria appear to outweigh the risks.