One bite is all it takes for Zika mosquito to transmit dengue

Washington D.C.: Turns out, a single mosquito bite might be enough to transmit multiple viruses.

A new study led by Colorado State University researchers found that Aedes aegypti, the primary mosquito that carries Zika virus, might also transmit chikungunya and dengue viruses with one bite. The findings shed new light on what's known as a coinfection, which scientists said is not yet fully understood and may be fairly common in areas experiencing outbreaks.

"A mosquito, in theory, could give you multiple viruses at once," said researcher Claudia Ruckert.

The CSU team infected mosquitoes in the lab with multiple kinds of viruses to learn more about the transmission of more than one infection from a single mosquito bite. While they described the lab results as surprising, researchers said there's no reason to believe that these coinfections are more severe than being infected with one virus at a time. Existing research on coinfections is sparse, and the findings are contradictory.

Chikungunya, dengue and Zika viruses are transmitted to humans by Aedes aegypti mosquitoes, which live in tropical, subtropical, and in some temperate climates. As the viruses continue to emerge into new regions, the likelihood of coinfection by multiple viruses may be increasing. At the same time, the frequency of coinfection and its clinical and epidemiologic implications are poorly understood.

Ruckert said the research team found that mosquitoes in the lab can transmit all three viruses simultaneously, although this is likely to be extremely rare in nature. "Dual infections in humans, however, are fairly common, or more common than we would have thought," she said.

CSU researchers had expected to find that one virus would prove to be dominant and outcompete the others in the midgut of the mosquito where the infections establish and replicate before being transmitted to humans.

"It's interesting that all three replicate in a really small area in the mosquito's body," Ruckert said. "When these mosquitoes get infected with two or three different viruses, there's almost no effect that the viruses have on each other in the same mosquito."Co-author Greg Ebel said the results were surprising.

"Based on what I know as a virologist, epidemiologist and entomologist, I thought that the viruses would either compete or enhance each other in some way," he said. "On the one hand, all of these viruses have mechanisms to suppress mosquito immunity, which could lead to synergy. On the other hand, they all likely require similar resources within infected cells, which could lead to competition. We didn't see much evidence of either one of these things in mosquitoes that were infected in the lab by multiple viruses."The study appears in the Nature Communications.