The virus, which causes flu-like symptoms in adults but can result in birth defects for pregnant women, has been detected in 60 countries around the world after an outbreak began in Brazil.

On Wednesday, the WHO said people who travel to countries where the virus is found should avoid sex half a year afterwards even if they have no symptoms, to minimise the chance of a pregnancy which carries defects such as microcephaly.

The agency had previously advised abstaining from sex for six weeks. However, Zika was subsequently found in the sperm of a man six months after he came into contact with the virus.

Sanjaya Senanayake, an Associate Professor of Medicine at at Australian National University who specialises in infectious diseases, said Australians travelling to Zika-affected regions including Singapore "should be cautious".

"Of course in countries with Zika there are other nasty mosquito-borne diseases like Dengue [Fever], so use maximum mosquito-avoidance measures," Dr Senanayake said. "Given we have found a man who's secreting Zika in reproductive fluids for six months, I think this is very good advice by the World Health Organisation."

Dr Senanayake said mosquito-borne infection with Zika was still the most common way of getting the virus, but sexual transmission - including women infecting men - was more common than initially thought.

Similar advice to abstain from sex had not been given for another virus, as far as he could recall, in recent memory.

"Having said that, we know with Ebola and in the context of the massive west Africa outbreak a year or two ago, we found that a lot of men were still excreting the ebola months afterwards, and there was a guideline to practice safe sex for quite a period," Dr Senanayake said.

"I guess the difference with Ebola and Zika is that Zika is now affecting about 60 different countries.

"The reality is, Zika wouldn't have been such an issue if it wasn't causing these birth defects, so the fact that it's hanging around in these reproductive fluids for so long is a concern."

The Zika virus has been around for many decades, but relatively small outbreaks until now mean doctors are constantly learning more about the virus and what it can do.

This means it is possible the virus could continue secreting in reproductive fluids for longer than six months, Dr Senanayake said.

"In ten years or so we'll look at what's happening now in the world with Zika, in this massive outbreak, as when we learned everything about Zika," he said.

While the Zika-carrying mosquito exists in far-north Queensland, Dr Senanayake said the chance of it spreading locally is "very low" because health authorities are monitoring it.

"I think Australians should be reassured by that, but just be careful when they're travelling to countries where there's a risk of transmission," he said.

He advised anyone who has returned from an area that has Zika, and is considering conceiving a baby, to consult a GP.