Why do Aedes mosquitoes catch and transmit dengue virus?

A number of viral diseases, such as dengue, Zika, Chikungunya, and yellow fever are transmitted to humans by the same intermediary: the Aedes aegypti mosquito. However, like other insects, this mosquito possesses antiviral defenses based the mechanism of RNA interference: small RNA molecules that can specifically degrade the genetic material of the virus, thereby blocking its multiplication and dissemination in the organism. Yet why is this system seemingly incapable of stopping dengue virus in the Aedes mosquito?

Teams from the laboratory Modèles insectes de l'immunité innée (CNRS/Inserm) and the Federal University of Minas Gerais (Brazil) have just discovered the existence in Aedes of a gene called Loqs2, which is indispensable to the proper functioning of RNA interference in the mosquito, but is not operative in its intestine! Without it, the viruses in the blood on which the mosquito feeds can multiply and subsequently infect its salivary glands. Aedes then transmits this virus during its next meal. Surprisingly, Loqs2 is not present in the genome of other related mosquitoes, which are not vectors of the virus. Researchers deduced that this gene could provide a key to understanding this distinctive feature of Aedes mosquitoes.