In what marks the most conclusive study yet on the virus, officials from the Centers for Disease Control and Prevention (CDC) confirmed the link between the mosquito-borne virus and microcephaly, the birth defect in which babies are born with small heads and under-developed brains.

They also highlighted wider issues resulting from the virus.

As well as microcephaly, Zika can cause miscarriages, premature birth, vision problems in babies, and other birth defects, according to research published in the New England Journal of Medicine.

Developing brain cells are also destroyed by the virus, researchers found.

“This study marks a turning point in the Zika outbreak,” said CDC director Tom Frieden in a statement.

“We are also launching further studies to determine whether children who have microcephaly born to mothers infected by the Zika virus is the tip of the iceberg of what we could see in damaging effects on the brain and other developmental problems.”

Zika, which can also be sexually transmitted, has been sweeping through Latin America and the Caribbean in recent months, with fears that the number of cases will increase during the summer.

It only causes a mild and brief flu-like illness of around three days in most people, but the risk for pregnant women has heightened fears. 

World Health Organization (WHO) advice, which is being following by the International Olympic Committee (IOC) and Rio organisers, is for women who are pregnant to not attend the Games.

A total of 1,113 cases of microcephaly have been confirmed in Brazil since October. 

Only around 200 of these have been in Rio de Janeiro, and, given that the Olympics and Paralympics will be held in winter months, the risk there is considered relatively low.

It is higher in other cities which are due to host matches during the Olympic football tournament.

Barely any mosquitoes have been seen here this week during the IOC Coordination Commission inspection visit that concluded today.

But the risk is more one of perception, and it is likely the findings will put off even more people from attending the Games, particularly in the US.

International ticket sales have decreased partly due to Zika fears, insidethegames understands, while at least one country, Liberia, is considering pulling out of the Games altogether partly because of concerns.

"Everyone coming to the Games does need to take Zika and other mosquito borne diseases seriously," IOC medical director Richard Budgett told insidethegames today.

"But we need to do so proportionately.

"The first thing to say is that we’re fortunate the Olympics is in the Winter."

In a more general sense, CDC officials are now vowing to be more blunt when speaking about Zika fears.

“We’ve been very careful over the last few months to say, ‘It’s linked to, it’s associated with,' - we’ve been careful to say it’s not the cause of,” said the CDC’s Director, division of Public Health Information and Dissemination, Sonja A Rasmussen.

“I think our messages will now be more direct.”