We know that mosquitoes are a serious threat to our health as humans – in fact, they are the world’s deadliest animal, with mosquito-borne diseases being more than responsible a million deaths a year.
And it’s not just their bites that we have to worry about. New research shows how a mosquito’s saliva carries the dengue virus is loaded with a substance that can suppress the response of our immune system and increase the risk of infection.
Using three separate analysis methods, the scientists identified a specific type of viral RNA or chemical messenger called sfRNA in the saliva of the infected mosquitoes. It essentially blocks the human body’s defense mechanisms against infection.
“It’s unbelievable that the virus can hijack these molecules so that their simultaneous delivery at the mosquito bite site gives it an advantage in establishing an infection,” says Biochemist Tania Strilets from the University of Virginia.
“These findings open up new perspectives on how we can counteract dengue virus infections from the very first mosquito bite.”
The sfRNA is loaded into membrane compartments called extracellular vesicles ready for delivery. The dengue virus appears to undermine “mosquito biology,” the researchers say, to give it a better chance to spread.
In tests on immortalized cell linesthe team confirmed that this sfRNA payload actually increased viral infection rates – laying the groundwork for the human body not being quite as well prepared for an attack.
These sfRNAs were sighted before transferred to insects virusesincluding Zika and Yellow Fever. More generally, their role seems to be to get in the way of the chemical signals the body uses when the virus is replicating.
“We propose that by introducing this RNA at the bite site of dengue-infected saliva, it prepares the terrain for efficient infection and gives the virus an advantage in the initial battle between it and our immune defenses,” write the researchers in their published work.
Dengue is a serious problem to have around 400 million people become infected every year – and reinfection is possible. Symptoms include fever, nausea, and a rash; in a small number of cases it can cause internal bleeding or even death.
At the moment there is no way to treat the virus, only methods to treat the symptoms. While we’re still a long way from a drug to treat dengue, it’s important to understand more about it and how it’s spreading in order to combat it.
The team hopes their discovery may lead to better preventive measures against dengue virus from the moment of infection, but the best way to protect yourself remains the same as before: avoid bites.
“I have no doubt that a better understanding of the basic biology of transmission will ultimately lead to effective measures to block transmission.” says Virologist Mariano Garcia-Blanco from the University of Virginia.
“Our results will almost certainly be applicable to infections with other flaviviruses. The specific molecules here probably don’t apply to them malariabut the concept is generalizable to viral infections.”
The research was published in PLOS pathogen.
