“Researchers have long wondered why Ae. aegypti mosquitoes don’t get sick when they are infected by these virusesour findings effectively solve this mystery and suggest a potential new mosquito-based disease control strategy that merits further study,” says study senior author George Dimopoulos, PhD, a professor in the Johns Hopkins Malaria Research Institute and in the Bloomberg School’s Department of Molecular Microbiology and Immunology.
The study’s lead author was Shengzhang Dong, PhD, a senior research associate in the Bloomberg School’s Department of Molecular Microbiology and Immunology.
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Each year these pathogens sicken millions of people around the world each year, killing tens of thousands. There are no antiviral therapies for any of these viruses. Currently, a vaccine is available for yellow fever virus. One dengue vaccine is approved by the Food and Drug Administration for individuals between six and 16 who have had prior dengue infection. Disease control methods for Ae. aegypti emphasize the use of insecticides, which have had limited success and have led to insecticide resistance.
Ae. aegypti mosquitoes are effective vectors of arborviruses because they can sustain significant infections with these viruses without suffering costs to their overall ability to reproducewhat biologists call “fitness.” If the mosquitoes’ fitness was impaired, they would likely have evolved strong defenses against these pathogens. Instead, they somehow ended up with a live-and-let-live balance that allows them to carry at least moderate viral loads without apparent adverse effects.
In the new study, Dimopoulos and Dong examined the role of Argonaute 2 (Ago2), a protein that in mosquitoes serves as part of an important antiviral mechanism known as the small interfering RNA (siRNA) pathway, which works by recognizing and destroying viral RNAs.
The researchers found that in Ae. aegypti mosquitoes lacking the Ago2 gene, the siRNA pathway is impaired, arborvirus infection becomes more severe, and the mosquitoes’ ability to transmit these viruses drops sharplyas they sicken, feed less, and often die within days.
The scientists showed that this increased mortality is caused not only by the impairment of the siRNA antiviral pathway, but also by defects in two other processes that happen to depend on Ago2: DNA repair, and a basic waste-removal process called autophagy. Ago2-deficient mosquitoes exposed to arborviruses were left with hyperinfections, extensive DNA damage, and the accumulation of molecular waste in their dying cells.
Apart from illuminating an important aspect of Ae. aegypti biology, the findings point to a possible new arboviral disease control strategy. This would be to engineer the mosquitoes so that arbovirus infections trigger the loss of their tolerance mechanisms, perhaps via the inhibition of Ago2. Arborvirus-carrying Ae. aegypti mosquitoes would thus die quickly, whereas the much greater number of non-arborvirus carrying Ae. aegypti should be unaffected.
“The biology of mosquito susceptibility and tolerance to infection is an interesting area of exploration for other pathogens as well,” says Dimopoulos. “For instance, mosquitoes that transmit malaria parasites could perhaps also be engineered to become sick and succumb to infection.”
Dimopoulos and his research group are now exploring possible ways of engineering Ae. aegypti to test this possible new disease-control strategy.
Source: Eurekalert
