BBC – Three to four million people could be infected with Zika in the Americas this year, the World Health Organization predicts.
Most will not develop symptoms, but the infection has been linked to brain defects in babies.
WHO director general Dr Margaret Chan said Zika had gone “from a mild threat to one of alarming proportions”.
She has set up a Zika “emergency team” after the “explosive” spread of the virus.
It will meet on Monday to decide whether Zika should be treated as a global emergency.