US health experts have confirmed that the Zika virus causes severe birth defects, including microcephaly. The US Centers for Disease Control and Prevention (CDC) has confirmed the link between the mosquito-borne virus and microcephaly, a syndrome which causes brain abnormalities in babies meaning they are often born with unusually small heads.

Although the Zika virus was first diagnosed in 1947 in Uganda, the 2015 outbreak in south America – most notably in Brazil – has seen much more serious symptoms in new born babies whose mother had contracted the virus. Brazilian doctors have confirmed at least 1,113 cases of microcephaly since October 2015 with almost 200 babies dying as result.

The Zika virus can be transmitted via mosquito and by sexual contact as well. Despite confirmation of the link, researchers will investigate why some cases of the virus result in birth defects while some women infected while pregnant give birth to healthy children.

Last year scientist from around the world jumped into action after a spike in Zika infections correlated with a rise in cases of microcephaly. The link was hard to establish as this is the first time that mosquito bites have caused birth defects, according to CDC head, Dr Tom Frieden.

"This study marks a turning point in the Zika outbreak. It is now clear that the virus causes microcephaly," said Dr Frieden.

In the US there have been 346 confirmed cases of Zika, in 30 states, all associated with travel to Latin America. On 11 April, US health officials urged Congress to pass $1.9bn (£1.3bn) in emergency funding

"Everything we know about this virus seems to be scarier than we initially thought," said Dr Anne Schuchat of the CDC. "Most of what we've learned is not reassuring".

The CDC says that the confirmation will help officials make a more convincing case to citizens urging precaution. They have previously warned pregnant women against travel to places where the Zika virus is spreading, mostly in Latin America and the Caribbean.

Research is continuing into a vaccine for the virus, but Dr Frieden has warned this could still be years from now.