Malaria

Each year, hundreds of thousands of people die from malaria and millions more suffer. We have intervened in the spread of malaria by using insecticides to control mosquito populations. However, mosquitos have begun to evolve resistance to the insecticides. What will happen when the insecticides no longer effectively keep mosquito population levels down? Scientists have proposed a “gene drive” to combat the spread of malaria.

Transmission

Plasmodium parasites cause malariaThese parasites reside in female Anopheles mosquitos. After a mosquito lays her eggs, she takes a blood meal to feed her young. When a female Anopheles mosquito bites a person, she injects saliva into the person’s blood. If the mosquito is infected, the Plasmodium parasites combine with the saliva and are also injected into the person.

The doublesex gene

Genes are encoded by DNA, and mosquitoes have two copies of every gene. Enzymes determine where the genes are in the DNA and create a molecule called messenger RNA (mRNA) based on the DNA’s sequence. This process is known as transcription. The enzyme can read the DNA in several different ways, and therefore can create different mRNA molecules from the same DNA sequence.

This is exactly what happens for the doublesex gene in mosquitoes. In females, the mRNA transcript of the doublesex gene contains a piece that is not present in the male mRNA transcript. This means that the same sequence of DNA is transcribed differently in female and male mosquitoes.

Using a genetic engineering tool called CRISPR-Cas9, scientists are able to modify the sequence of the DNA right next to the particular part of the doublesex gene that is transcribed differently in females and males. This means that when males have this modified gene, their mRNA is totally normal, and therefore the males are normal. But when females have this modified gene, their mRNA is abnormal. When females have two copies of the modified doublesex gene, they are unable to lay eggs and cannot bite.

Gene drive

If a male Anopheles mosquito with the mutated doublesex gene mates with a female Anopheles mosquito, their offspring will contain the mutated doublesexgene. If many genetically engineered male mosquitoes were released into the environment, they would mate with the female mosquitoes in the environment and the gene would “drive” its way through the mosquito population. Because females with two copies of the gene are unable to lay eggs, the mosquito population would collapse. This was tested on caged mosquitoes: within 7-11 generations, the mosquito population successfully crashed due to the gene drive.

Next steps

More research is needed into the effects of using this genetic engineering technology outside of a laboratory setting. However, genetically engineering mosquitoes to prevent malaria is an exciting prospect and demonstrates the power of genetic engineering to help humanity.

References:

https://www.nature.com/article...

https://www.who.int/en/news-ro...

https://www.cdc.gov/malaria/ab...

https://www.npr.org/sections/g...

https://www.npr.org/sections/h...