As scientists continue to study the Zika virus, researchers have found that children with a history of dengue infection had a significantly lower risk of being symptomatic when infected by Zika, according to a study in Nicaragua of more than 3,000 children.
Experts worried that prior dengue infection could worsen Zika disease, but the findings published in the journal PLOS Medicine suggest that dengue immunity in children may protect against symptomatic Zika, which can cause fever, rash, joint and muscle pain, and red eyes.
The researchers, led by Aubree Gordon of the University of Michigan and Eva Harris of the University of California, Berkeley, said prior dengue exposure did not prevent the children from contracting the Zika virus, but that, if they did, they were less likely to get sick.
Zika and dengue are both are spread primarily through the bite of an infected Aedes aegypti mosquito.
There is no treatment or vaccine for Zika or dengue. But dengue has been entrenched in the Americas for decades, while Zika was not reported in the region until 2015. Since then, scientists have been studying Zika disease, which causes symptoms in about one of five people who are infected and can cause severe birth defects.
Since dengue and Zika are closely related — and because a second dengue infection can sometimes be much more severe than the first — scientists wanted to know whether Zika following a dengue infection could also be more severe.
To answer the question, researchers studied the 2016 epidemic of Zika among a group of children in Managua, many of whom had a history of dengue. Among the 3,893 children younger than 14 who were studied, researchers estimated there were 1,356 Zika infections — 560 of which were symptomatic — from January 2016 through February 2017. Cases were confirmed by laboratory testing.
Children with prior dengue infections had a 38 percent lower risk of developing Zika symptoms when infected than children who had not had a dengue infection, the researchers found.
Researchers said they do not yet understand how dengue can provide some protection from the Zika virus. And they don’t know whether the opposition protection also holds true — that a Zika infection could provide some immunity to dengue. But they said that more research to understand that relationship could one day be used to help develop a vaccine.