Zika is a Lot Like Other Tropical Fevers

Zika is spread mostly by the bite of an infected Aedes species mosquito (Ae. aegypti and Ae. albopictus). These mosquitoes bite during the day and night.

There is no vaccine or medicine for Zika. In most ways, Zika is a lot like other tropical fevers. People become infected when they are bitten by mosquitos. Infected mothers pass the virus to their unborn children.

‘People with Zika virus disease can have symptoms including mild fever, skin rash, conjunctivitis, muscle and joint pain, malaise or headache. These symptoms normally last for 2-7 days.’

But unlike other mosquito-borne outbreaks, Zika doubles as a sexually transmitted infection, passing from person to person in bodily fluids. And that's where things get complicated.

In a new paper, a team led by Santa Fe Institute Research Fellow Laurent H�bert-Dufresne asks under what conditions a Zika outbreak might be sustained where mosquitos play no role.

"Zika has a lot of unusual characteristics that have caused scientists a lot of confusion," says H�bert-Dufresne. "Infected people rarely have symptoms, and typically only reproducing women get tested, so we know very little about the true extent of Zika's sexual transmission."

One Zika oddity is that infected males retain the virus in their semen nearly 10 times longer than women do in their vaginal fluids -- 180 days rather than 20, on average -- making males much more likely to transmit Zika sexually than females.

That raises a question: Could a population of males who have sex with males sustain an outbreak once the virus gets going -- when an infected male returns from visiting a place where Zika-carrying mosquitos are active, for example?

To study the problem, the research team generated hypothetical sexual contact networks, randomly assigning sexual orientations to its members. Then they let the networks percolate.

"We wanted to know what's the biggest outbreak we can get," says H�bert-Dufresne.

They found that their random networks quickly developed core-periphery structures, with populations of males who have sex with males forming an outbreak-sustaining core and the heterosexual population experiencing smaller outbreaks on the periphery.

Males who have sex with males, of course, are part of a wider sexual contact network in which bisexual males pass the virus to their female partners, who pass the virus to their partners, and so on. In the researchers' networks, Zika outbreaks make their way into the heterosexual community but soon peter out under the less-probable female-to-male transmission conditions.

The possibility of silent, sustained outbreaks among populations least likely to get tested for Zika should raise alarms, says H�bert-Dufresne.

"Because people usually don't have symptoms, we mostly care about Zika when it goes into the community of reproducing females," he says. "But if there are hidden reservoirs of Zika infection out there that can get into the reproducing population, we might want to rethink our surveillance and prevention strategies."

Source: Eurekalert