Mosquito spit can increase dengue severity
Blood vessels weakened by saliva may accelerate spread of virus
A mosquito’s spit can be worse than its bite alone. In some cases, the insect’s saliva makes the viral disease dengue fever more severe, a new study finds.
In mice, scientists found that mosquito spit weakened blood vessels, making them more permeable, or “leaky.” Easier exchange between the blood and tissues may help the virus spread faster — and increase the severity of disease — immunologist Michael Schmid and colleagues report online June 16 in PLOS Pathogens.
Dengue virus enters the bloodstreams of nearly 400 million people a year, through the sharp proboscises of tropical Aedes mosquitoes, which also deliver a spit-load of other molecules as they slurp a meal. There are four strains of dengue, which can cause bone and muscle aches, high fever and, in severe cases, death. Overcoming one type of dengue doesn’t protect the host from the other three strains. In fact, subsequent infections are often worse (SN: 6/15/16, p. 22).
Immune cells fight off the first dengue infection, and the body develops antibodies to that strain. But during a subsequent episode with a different variety of dengue, the antibodies from the first infection don’t kill the second — they amplify it. They pull new virus into healthy cells.
Scientists have studied this strange immune trap for three decades, “but what we didn’t know was that saliva could exacerbate it,” says Schmid, now at the University of Leuven in Belgium.