Will Releasing Genetically Modified Mosquitos Finally Conquer Malaria?
For the first time, scientists have shown that a new kind of genetic engineering, known as a “gene drive,” can crash populations of malaria-spreading mosquitoes.
The objective of the study was to alter three species of mosquito most responsible for disease transmission – Anopheles gambiae, A. coluzzii and A. arabiensis. The photo above shows an infected erythrocyte with the characteristic malaria ring form.
Despite years of effort, malaria remains a major health problem. This mosquito-borne parasitic disease infects more than 200 million people every year and kills more than 400,000, many of whom are children. 1 Worldwide, it is the fourth biggest infectious disease killer behind tuberculosis, HIV/AIDS, and hepatitis C.
Dr. Ruth Müeller, PhD, and her colleagues utilized CRISPR to make precise edits to the Anopheles species. CRISPR, shorthanded for CRISPR-Cas9, acts as “molecular scissors” that cut DNA at a specific location when guided by a RNA template. Once snipped, the cell activates a DNA repair mechanism and scientists can use this mechanism to introduce, delete, or mutate a gene of interest. 7
In this study, the modification consisted of a mutation in a gene known as “doublesex” which female mosquitoes need for normal development. While genetically female, the transformed insects have distorted mouths, resembling their male counterparts; which prevent them from biting and spreading malaria. In addition, the females’ reproductive organs are deformed preventing them from laying eggs. 2 Essentially, the mutated gene converts female mosquitos into males, thus drastically reducing the population of the mosquitos capable of carrying and transmitting the malaria parasite.
“[This] gene drive is like a ‘selfish gene’…. All the mosquito offspring – have this modification,” Müeller says. “The idea and hope is that they would spread their mutation and eventually sterilize all the females. That would crash – or drastically reduce – local populations of the main species of mosquitoes that spreads malaria”.6
To safely test the mosquitoes under more natural conditions, researchers built a special high-security lab in Italy (far away from Africa) designed to keep the mutated mosquitoes from escaping. The researchers then released dozens of the gene-drive mosquitoes into special large cages containing hundreds of wild-type mosquitoes. The gene-driven mosquitoes decimated the natural mosquito populations in less than a year. 5, 2
Some researchers are welcoming the advance while others are highly skeptical and say the technology is too dangerous. Dr. Ethan Bier, PhD, noted, “One should never predicate the use of a gene drive…Just like with insecticides, you can expect that the insect will become resistant one way or another. The drive itself [could] create a mutation preventing the drive from going further.”4
Dr. Alekos Simoni, PhD, cautiously noted, “Looking at the roles of Anopheles mosquitoes is crucial in terms of the food web, pollination and the general ecosystem. I think there can be a problem for species that are distributed around the world like the mosquito because it is difficult to constrain in the area”.4
So what does the future hold for gene drives? Whether gene drives will end up being utilized as a tool to control wild populations or remain a tool to be used in the lab, remains to be seen. It is a complex issue, with valid arguments being made for and against the use of the technology.
by Francisco Pinon