Saturday, September 7, 2019

Genetic Modification of Mosquitoes leading to Self-destruction

Mosquitoes can be classified as major pests, especially with their potential to spread vector-borne diseases. These pests are especially potent in third-world countries, specifically Africa where malaria kills more than 400,000 people each year (Stein). After attempting to hack the mosquito genome to prevent mosquito populations from increasing for almost 8 years, two geneticists have finally achieved some promising results in 2011. Austin Bart and Andrea Crisanti, researchers at Imperial College London, inserted a gene that reached more than 85% of mosquito descendants within a population in a short amount of time. This new technology was the first ever engineered gene drive.

A gene drive is defined as a genetic modification designed to spread through a population at a higher than normal rate compared to inheritance. The gene drive relies on a fairly recent technology called CRISPR and some bits of RNA to alter or silence a specific gene or to insert a new one entirely. Within the next generation, the whole drive copies itself onto its partner chromosome so that the genome no longer has the natural version of a chosen gene. Instead, the generation will have two copies of the gene drive. With the gene drive in place, the gene is passed up to 100% of the offspring; compared to 50% of the offspring through standard inheritance. 

Gene drives have a lot of potential, including the ability to reduce or eliminate insect-borne diseases, controlling invasive species, and reversing insecticide resistance in pests. Although gene drive technology is promising, many questions still remain on how effective it will be when introduced to the wild. Some even question if it will even work, especially since some experiments with fruit flies have indicated resistance to the edited gene drive. However, Bart and Crisanti remain hopeful with their experiments on Anopheles gambiae (a vector for malaria) resulting in the inability for female mosquitoes to bite and lay eggs. It is key for geneticists to target the right gene, as some are highly conserved and would not do well with any mutations. Bart and Crisanti created a drive that would disrupt the doublesex gene in the A. gambiae species. This doublesex gene is crucial for fertility, so the gene is resistant to any kind of mutation. No eggs were produced by the females within 8 to 12 generations, essentially wiping out an entire population of potential malaria-spreading mosquitoes.

Even if the gene drives do prove successful, some ethical issues also rise. Is it just to wipe out entire populations of pests and going against mother nature through accelerated extinction? Is it right to test and release these mosquitoes in developing countries where the consequences are not yet known? What will happen when the gene drives do wipe out entire communities of pests? Fredros Okumu, director of science at Ifakara Health Institute in Dar es Salaam, Tanzania, believes it is important for people to spread information on the technology and to prepare them for what the gene drive will do to mosquito populations in their countries. Okumu also wants African scientists to work with and test gene drives locally, so a trust can be developed between scientists and locals (Scudellari).

Of course, gene drives will need many more tests before they can be fully introduced to the wild. Only a small fraction of mosquito species in the wild actually transmit disease, so the potential to wipe out the few hundred species of disease-carrying mosquitoes is ground-breaking. Not only will it prevent the spread of disease, it will save the lives of hundreds of thousands of people.


1 comment:

  1. I enjoyed reading this article because it talks about CRISPR and a mosquito vector. CRISPR is a powerful gene-editing tool that can help save millions of lives and potentially eliminated mosquito vectors such as Aedes, Anopheles, Culex and Culiseta. These vectors can transmit some serious and painful diseases like dengue, malaria, yellow fever, zika virus, arboviral encephalitis and chikungunya. I think the community needs to be well informed about such experiments and their outcomes beforehand so everyone can discuss the important ethical issues since arthropod genes are not the only genes CRISPR can modify. I am hopeful about CRISPR.