The World Health Organization on Thursday warned women against traveling to areas with ongoing Zika virus transmissions, including Rio de Janeiro, site of the 2016 Olympics.
"There is scientific consensus that Zika virus is a cause of microcephaly (children being born with unusually small heads) and other brain malformations and disorders in babies born to women who were infected with Zika virus during pregnancy," the U.N. health agency said.
WHO urged the sex partners of pregnant women to practice safe sex or abstain from sex for the remainder of the pregnancy, if they have recently returned from visits to Rio or other areas where the virus is circulating.
The agency also advised all Olympics visitors and athletes heading for Rio or other virus-affected areas to wear clothing that covers much of the body and to use insect repellent. In addition, they should stay in rooms that are air-conditioned and keep windows closed, the agency said.
Because Zika can be transmitted through unprotected sex, WHO said travelers should use condoms while in Rio, and for four weeks after leaving the country, they should abstain from sex altogether.
Visitors were advised people to avoid impoverished and overcrowded areas of the huge city, such as those that lack proper sanitation or water mains.
About 500,000 tourists are expected to travel to Brazil for the Olympics, which run from August 5 through September 18.
Earlier this week, a Canadian professor said the games should either be postponed or moved elsewhere because of the Zika outbreak, to avoid spreading the virus even more widely around the globe.
Brazil has been at the epicenter of the Zika outbreak, which affects 58 countries and territories.
Officials from the International Olympic Committee say there is no justification for moving the games, and that they are confident about precautions being taken by the World Health Organization to address the Zika outbreak.
