This story is part of a partnership between MedPage Today and VICE News.
The World Health Organization is advising women living in areas where the Zika virus is being transmitted to delay getting pregnant, advice already given by several countries where the virus is in widespread transmission.
The WHO issued the advice last week, but its meaning only became clear on Thursday when the health agency issued a correction to its advice on preventing sexual transmission of the virus.
Although Zika is primarily spread by mosquitoes, it can also be spread through sexual transmission. In women who are pregnant, this exposes the fetus to the risk of microcephaly, a birth defect marked by small head size and underdeveloped brains. Concerns over microcephaly led WHO to declare Zika a global health emergency on Feb. 1.
WHO's advice now expressly states that men and women of reproductive age living in affected areas should consider delaying pregnancy. The advice does not say for how long. It will affect men and women in some 60 countries.
There have been 618 Zika cases reported in the continental United States as of June 1, but no cases were acquired from local mosquitoes. In US territories, like Puerto Rico, there have been 1,114 cases. All but four were acquired from local mosquitoes. And public health experts say they're sure the virus can cause microcephaly in babies whose mother caught the virus during pregnancy, causing them to be born with abnormally small heads and underdeveloped brains.
"The rapidly evolving outbreak of Zika warns us that an old disease that slumbered for six decades in Africa and Asia can suddenly wake up on a new continent to cause a global health emergency," WHO Director-General Dr. Margaret Chan said during her address to the 69th World Health Assembly in Geneva, Switzerland. "Confirmation of a causal link between infection and microcephaly has transformed the profile of Zika from a mild disease to a devastating diagnosis for pregnant women and a significant threat to global health."
Take a look at how the outbreak unfolded by clicking through the timeline below.
Reuters contributed to this report.