The spread of the Zika virus in Brazil has been casting a long shadow over preparations for the 2016 Olympics in Rio de Janeiro, but organizers remain confident the Games will go ahead as planned.

The International Olympic Committee (IOC) has said it has drawn up guidelines aimed at protecting the thousands of athletes and 500,000 fans expected to visit the city from August 5 to 21.

The virus is transmitted by mosquitoes and while the initial symptoms are relatively mild in most people, Zika is believed to be linked to microcephaly, which causes babies to be born with shrunken heads and damaged brains. There is currently no treatment or vaccine for Zika.

Cases of microcephaly have risen dramatically in Brazil in recent weeks and the World Health Organization, which has warned that 3 to 4 million people cold become infected with Zika, has called an emergency meeting for Monday to decide whether to declare a public health emergency.

Brazilian winter could reduce the risk

However, IOC President Thomas Bach said on Thursday that the timing of the Games would help reduce the risk of infection.

"The Olympic games will take place during the Brazilian winter so at that time we will have different climate conditions than there are now, when we are in the middle of the Brazilian summer," he said, adding that the IOC was working in "close cooperation" with Brazilian authorities.

His view is shared by Rio de Janeiro Mayor Eduardo Paes who said he didn't believe Zika "is a problem for the Olympics."

Others are not so sure and some commentators have expressed concerns about the virus spreading to the United States. Earlier this week, US health officials advised pregnant women against travelling to Brazil and other nearby countries.

Australian Olympic team medical director David Hughes has also expressed reservations.

"All females of child-bearing age need to be aware of the specific risks of microcephaly in newborns, should the mother become infected during pregnancy," Hughes told news portal news.com.au.

"Following the recently updated DFAT (Australia's Department of Foreign Affairs and Trade) guidelines, any team members who are pregnant at the time of the Games need to consider the risks very carefully before deciding whether to proceed with travel to Brazil."

mp/pfd (AFP, AP)