We know that mosquitoes are a serious threat to our human health - in fact, they are the world's deadliest animal, and mosquito-borne diseases kill more than 1 million people each year.

It's not just their bites that we need to worry about. New research suggests that the saliva of mosquitoes carrying the dengue virus contains a substance that may suppress our immune system's response and increase the risk of infection.

Using three different analytical methods, scientists found a specific type of viral RNA, or chemical messenger, called sfRNA in the saliva of infected mosquitoes. it essentially blocks the body's defense mechanisms to fight off infection.

Tania Striles, a biochemist at the University of Virginia, says: "Incredibly, the virus can hijack these molecules so that their co-delivery at the mosquito bite site gives it an advantage in establishing infection." "These findings provide a new perspective on how we can fight dengue virus infection from the first bite of the mosquito."

The sfRNA is loaded in membrane compartments called extracellular vesicles, ready for delivery. In the researchers' words, the dengue virus appears to "subvert the biology of the mosquito" and give it a better chance of spreading.

In tests on immortalized cell lines, this sfRNA payload did increase the level of viral infection, setting the stage for the body to be well prepared for an attack.

These sfRNA have previously been found in arboviruses including Zika and yellow fever. more generally, their role appears to be to impede the chemical signaling used by the body during viral replication.

In their published paper, the researchers wrote: "We suggest that by introducing this RNA at the site of the bite, dengue-infected saliva prepares the terrain for effective infection and provides an advantage in the first battle between the virus and our immune defenses."

Dengue fever is a serious problem, with approximately 400 million people infected each year and at risk of re-infection. Symptoms include fever, nausea and rash; in rare cases, it can lead to internal bleeding and even death.

There is no cure for the virus, only a way to control the symptoms. While we are still always away from developing a cure for dengue, learning more about it and how it spreads is crucial to fighting it.