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.

A new study 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. The research team's paper was published in Nature Communications.

The 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.

Author 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," author said.

The 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," author 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."

What is the threat for people diagnosed with a coinfection?

"There's no strong evidence that coinfection of humans results in infections that are clinically more severe," author said.

But findings are contradictory. A team in Nicaragua looked at a large number of coinfection cases in one study, but saw no changes in hospitalization or clinical care. But other studies found a possible link between neurological complications and coinfection.

It is also likely that coinfections in humans are significantly underdiagnosed.

The team is also interested in learning more about where the viruses replicate in mosquitoes, and by potentially examining yellow fever, a fourth virus that is carried by Aedes aegypti, as a possibility for coinfection with chikungunya, dengue or Zika viruses.

http://source.colostate.edu/mosquitoes-spread-zika-virus-simultaneously-transmit-viruses/