WASHINGTON — The World Health Organization on Tuesday expanded its guidance on preventing Zika, warning that everyone who visits a Zika-infected zone should practice safe sex for six months, even if they show no symptoms of the disease.
The new recommendation applies to men and women, a significant change in the United Nations agency’s view of the dangers of sexual transmission. Previously, only men with symptoms of the disease were told to practice safe sex for six months. For women, the period was eight weeks.
The U.S. Centers for Disease Control and Prevention said it was considering updating its own guidance on safe-sex practices in light of the WHO recommendation.
“As CDC has said repeatedly, we are in a fast-changing research environment with the Zika virus,” said Benjamin Hayes, a CDC spokesman. “We are carefully reviewing all of the latest scientific information and will update our guidance when the review is complete.”
The CDC currently recommends that men and women returning from areas where Zika is prevalent abstain from sex or use condoms and barriers for eight weeks if they show no symptoms. Because of the time Zika is thought to remain in semen, men who show symptoms should wait at least six months before having unprotected sex, the CDC has cautioned. Women are advised to wait eight weeks after first showing symptoms.
But WHO officials say that is no longer long enough.
The new guidelines reflect growing concern among health officials about the role of sex in spreading the virus, which can have a catastrophic effect on fetuses, including a brain disorder characterized by microcephaly, and can cause neurological complications and Guillain-Barre syndrome in adults.
Sexual transmission had initially been thought to be relatively rare. But the spread of the virus worldwide — including into northern areas where the primary source of the disease, the Aedes aegypti mosquito, is not prevalent — suggests a far greater role for sex in Zika transmission.
“Mounting evidence has shown that sexual transmission of Zika virus is possible and more common than previously assumed,” the WHO said in its new guidelines.
While experts agree mosquitoes remain the main concern, recent studies indicate that women have been infected with the virus more often than men have, possibly because of sexual transmission. Researchers also think that women can transmit the virus to their partners and have cautioned previously that women having sex with other women should also practice safe sex if they’ve possibly been exposed to Zika.
Eleven countries have reported cases of sexually transmitted Zika, according to the WHO. CDC officials know of 23 sexually transmitted cases in the continental United States. Officials were preparing to begin Thursday aerial spraying for mosquitoes amid a Zika virus outbreak in Miami Beach, Fla.
A major challenge in identifying the Zika virus is that the symptoms are so mild. They include a fever, headache and possible red eyes. But most people don’t ever realize they have the disease.
The WHO said last week that the growing spread of Zika around the world and basic gaps in knowledge about the virus’s devastating complications in babies continue to make Zika a global health emergency.
The developments came as a new study identified eight countries in Asia and Africa that researchers say are at the greatest risk of Zika virus transmission.
The Washington Post and Miami Herald contributed.
First Published: September 7, 2016, 4:00 a.m.
