The US Centers for Disease Control and Prevention (CDC) has confirmed that the Zika virus causes severe birth defects, including microcephaly.
Thousands of babies were born in Brazil last year with microcephaly, a syndrome where children are born with unusually small heads.
The defects coincided with a spike in Zika infections, leading experts to suspect the mosquito-borne virus.
Growing research has now affirmed those experts’ suspicions, the CDC said.
“This study marks a turning point in the Zika outbreak. It is now clear that the virus causes microcephaly,” said Dr Tom Frieden, the head of the CDC.
CDC officials said the findings do not change the agency’s earlier guidance to pregnant women.
The CDC has discouraged pregnant women from travelling to places where the Zika virus is spreading, mostly in Latin America and the Caribbean.
Dr Frieden said intensive research was under way to find out much more about the mosquito-borne virus and to develop a vaccine for it, although he warned that that could still be years away.
This is the first time that mosquito bites have caused birth defects, Dr Frieden said. The virus can be transmitted by sexual contact as well.