A new way of fighting mosquito-borne disease
Researchers have demonstrated that single gene manipulation in female Aedes aegypti mosquitos is able to convert them into nonbiting males
Mosquito-borne diseases are an ongoing risk in many parts of the world including Africa and the Middle East. They are spread by the bite of an infected mosquito; whose body serves as an incubator for the reproduction of a parasite or pathogen responsible for human disease e.g. malaria, Zika virus, dengue. In the case of malaria, the parasite itself replicates in human red blood cells and destroys them, releasing daughter parasites which are spread by mosquitos taking blood from one person to another. This kind of cyclical infection ensures the successful transmission of disease and is the reason why such illnesses propagate so easily.
Treating mosquito-borne diseases is extremely difficult and depends on a number of factors. One increasing problem is parasite resistance to drugs, which means that previously effective medications are no longer able to treat the disease. Just like the issue of antibiotic resistance, parasite resistance can occur due to incorrect use of drugs which create a selective pressure for specific mutations in the DNA of the parasite that protect it against the medicine itself. Whilst such diseases can be spread from person to person by other means than just mosquito bites, scientists agree that in order to prevent the emergence and continuance of these diseases research must specifically target these insects.
Female Aedes aegypti mosquitoes are ideal vectors for pathogens which cause Zika and dengue fever. Male mosquitoes on the other hand, do not bite and are therefore unable to infect humans with such pathogens.
Researchers from Virginia Tech have identified a prime genetic difference which determines the sex of a mosquito, known as the male-determining locus (M locus). The M locus is a region of a chromosome which contains 30 genes, including Nix, a specific gene responsible for the male sex of an offspring. The way this works is similar to the human Y chromosome which is only inherited by males, therefore this is known as a ‘male-determining factor’. The researchers found that by inserting the M locus into a chromosomal region which is inherited naturally by female mosquitoes, it was able to convert females to male mosquitoes. Importantly, Nix alone was sufficient to convert the sex of the mosquito. They found this out by inserting each of the 30 genes into the female chromosome and realising that only Nix had this capability.
The researchers worked with mosquitoes at the embryonic stage of development and found that by adulthood, the newly-converted males had male sex organs but female antennae. These new males were fertile, and their offspring also had the Nix gene inserted in the same place on the chromosome. This indicates that the sex conversion was 100% effective, heritable and stable i.e. does not fade over generations.
The research of these scientists shows great potential for future mosquito-control strategies which could be used to manage, prevent or even eradicate mosquito-borne diseases. Whilst complete extermination of mosquitoes would be unethical, changing the male-to-female ratio could be the best way to reduce the likelihood of mosquito-to-human disease transmission.
- Azadeh Aryan, Michelle A. E. Anderson, James K. Biedler, Yumin Qi, Justin M. Overcash, Anastasia N. Naumenko, Maria V. Sharakhova, Chunhong Mao, Zach N. Adelman, Zhijian Tu. Nix alone is sufficient to convert female Aedes aegypti into fertile males and myo-sex is needed for male flight. Proceedings of the National Academy of Sciences, 2020; 202001132 DOI: 10.1073/pnas.2001132117