The World Health Organization on Tuesday toughened its advice on preventing the spread of Zika, saying anyone returning from areas hit by the virus should practice safe sex for six months afterward.
The updated guidelines mean the U.N. health body’s recommendations regarding sexual transmission are now the same whether or not people are showing symptoms of the virus.
“WHO recommends practicing safer sex or abstinence for a period of six months for men and women who are returning from areas of active transmission … to prevent Zika virus infection through sexual transmission,” the agency said.
The WHO suggested in June that men should avoid sex or use protection for eight weeks after coming back from visits to affected places if they did not show symptoms.
“Mounting evidence has shown that sexual transmission of Zika virus is possible and more common than previously assumed,” the WHO said in guidelines released Tuesday.
Zika is primarily a mosquito-borne virus that causes no symptoms in four out of five of those affected.
But if pregnant women are infected, they face a higher risk of having a baby with head and brain defects, a condition known as microcephaly.
The WHO also recommended on Tuesday that people in Zika-hit areas be offered a full range of contraception options in order “to make an informed choice about whether and when to become pregnant.”
The Zika virus can live in eyes, researchers meanwhile said Tuesday, after conducting experiments on mice that may explain why some patients develop ocular disease and in some cases become blind.
The study, published in the journal Cell Reports, studied the effects of Zika virus infection in the eyes of fetal, newborn and adult mice.
“Our study suggests that the eye could be a reservoir for Zika virus,” said Michael Diamond, a professor at the Washington University School of Medicine in St. Louis who is one of the study’s senior authors.
“We need to consider whether people with Zika have infectious virus in their eyes and how long it actually persists,” he added, noting that patients could spread the infection through their tears.
The researchers are planning to expand their study to include humans infected with Zika virus.
Zika causes only mild symptoms such as fever and a rash for most people but pregnant women who catch it can give birth to babies with microcephaly, a deformation marked by abnormally small brains and heads.
One third of babies infected with Zika in utero have eye disease such as inflammation of the optic nerve, retinal damage or blindness, the researchers said.
In adults, Zika can cause conjunctivitis, also known as pink eye, and in some rare cases uveitis, a condition in which part of the eye wall becomes inflamed. It can lead to permanent vision loss.
In conducting the study, researchers infected mice under the skin, similar to the way a human would be infected by a mosquito.
They found live Zika virus in the rodents’ eyes seven days later.
Infection in the eyes means it’s possible people can become infected with Zika simply through touching contaminated tears.
It’s still not clear how the Zika virus makes its way to the eyes. One possibility is that it crosses “the blood-retina barrier that separates the eye from the bloodstream, traveling along the optic nerve that connects the brain and the eye,” researchers said in a statement.
Researchers found genetic material from Zika in the tears of infected mice 28 days after infection — though not the virus itself.
“Even though we didn’t find live virus in mouse tears, that doesn’t mean that it couldn’t be infectious in humans,” said lead author Jonathan Miner, who teaches medicine at Washington University.
“There could be a window of time when tears are highly infectious and people are coming in contact with it and able to spread it.”