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Mosquitoes, despite their tiny size, are classified as one of the deadliest insects in the world. Millions of people are affected by infectious mosquito-borne diseases each year, and two million reportedly die annually. But the risk of contracting an infectious mosquito-borne disease at home or overseas could soon be lessened, thanks to recent genealogical studies by entomologists at Virginia Tech in the US.
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Researchers have recently discovered a sex-determination gene in mozzies called Nix that controls whether mosquitoes either become male or female. This can be manipulated to make mosquito populations have a larger amount of males. The males are harmless because they only feed on nectar. It’s the female mosquitoes who are blood-eating and vectors of diseases, such as dengue fever, malaria, yellow fever and the west Nile virus.
Virginia Tech entomologists Zach Adelman and colleague Zhijian Tu, published a review called “Trends in Parasitology” in February 2016 to outline the approach. In the review Adelman says that genetic engineering is giving them a good understanding of how mosquitoes determine whether to become a male (what we want) or a female (trouble for us) and how they can permanently modify wild populations using gene drive techniques.
In the past mosquitoes have been successfully genetically modified and released into the wild to help control the outbreaks of dengue fever and malaria. The process, however, is time-consuming with thousands of eggs needing to be injected to create just one genetically modified egg. It is also expensive and difficult to implement on a large scale.
But with the discovery of the Nix gene Adelman and Tu are saying this kind of genetic modification could be the answer to seriously reduce mosquito populations. Using the CRISPR-Cas9 system, which can introduce mutations at virtually any genomic site, the Nix gene can be triggered to convert female mosquitoes to male ones or simply kill them off.
Says co-author Zhijian Tu, “Either outcome would help to reduce mosquito populations and improve sex separation procedures, which are required in any genetic strategy to prevent the accidental release of disease-transmitting females into wild populations.”
However, there are technological and ethical concerns that need to be addressed before the Nix gene drive system can be applied in the field. It is thought that the approach will likely be tested in locations most impacted by mosquito-borne diseases and where other control measures haven’t worked. Government and public support will also be necessary for field-based testing.
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