Mosquitoes: Our Deadliest Enemy
Mosquitoes are our species’ largest historical killer. Some estimate they may have killed half of all humans who ever lived. Today, they infect hundreds of millions of people every year and kill someone every twelve seconds. Malaria stands out in the crowded field of mosquito-borne illnesses: it collectively takes 45 million years off human lives per year, while most other mosquito-borne diseases barely cross a million. It’s no wonder, then, that countless technologies have been developed to combat malaria. Among the most promising: gene drives.
A mosquito, like a human, inherits two copies of each gene, one from each parent. Both copies may have the same or different ‘alleles,’ or versions of, the gene. If one of its parents has been genetically modified with a gene drive, the mosquito will inherit one modified allele, while the other copy of the gene will be the ‘wild-type’ allele found in the general population. The altered allele cleverly encodes not just for a different version of the gene but also pieces of molecular machinery (guide RNA, Cas9, etc.) that snip out the wild-type allele. The modified cell then fixes the gap by copying the modified allele to replace the lost wild-type one, giving the mosquito two copies of the modified characteristic which it can then pass onto its offspring. Here are three ways that gene drives can fight malaria:
1. Since only female mosquitoes transmit malaria, skewing the sex ratio of offspring from roughly equal to almost 95% male can result in an entirely unisex population in as few as ten generations, resulting in a decrease in transmission of malaria and, in general, rapid population collapse.
2. Female mosquitoes can also be targeted by inserting female-sterility genes that, say, eliminate their ability to lay eggs or prevent those eggs from hatching. As these genes proliferate, female fertility will reduce and the number of mosquitoes available to spread disease will decrease.
3. Another option is making mosquitoes resistant to Plasmodium, the parasites that cause malaria. A promising study from last September found that modifying the gut genes of mosquitoes to promote secretion of antimicrobial amino acids stopped them from carrying and transmitting Plasmodium.
In sum, gene drives are a possible solution to eliminating malaria. The tightly-controlled yet rigorous tests occurring in labs and field locations around the world today will lead to the first informed, large-scale use of this powerful technology tomorrow!
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