The Zika virus “is now spreading explosively” around the Americas, the head of the World Health Organization said Thursday, calling the level of alarm over the disease “extremely high.” “The level of concern is high, as is the level of uncertainty,” WHO Director-General Dr. Margaret Chan told her organization’s executive board members. “We need to get some answers, quickly.” The mosquito-borne disease is now in “23 countries and territories in the region,” according to Chan.

While it’s been around in some form for decades, alarms have been raised only recently about Zika’s suspected connection with “birth malformations and neurological symptoms.” “Arrival of the virus in some places has been associated with a steep increase in the birth of babies with abnormally small heads and in cases of Guillain-Barre syndrome,” Chan explained. After being first detected in 1947 in a monkey in Uganda, Zika was most often found along the equator from Africa into Asia. Nine years ago, new cases popped up in islands in the Pacific Ocean. FULL REPORT