Male Olympians and men travelling to countries where the Zika virus is actively transmitted have been advised to practise safe sex for three to six months once back in New Zealand.

Dr Stewart Jessamine, the acting director of public health, appeared today before Parliament's health committee with other officials from the Ministry of Justice to give a briefing on the Zika virus.

He said official advice to Olympians and those travelling to countries where the Zika virus is actively transmitted remained the same: practice safe sex, and take steps to avoid mosquito bites such as wearing repellent and clothing that covers skin.

"The only thing we have now added is, and, if you are a man, you should probably practice safe sex for three to six months after you return. That is the key bit of information."

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Dr Jessamine said time frame was something of a "semi-informed best guess", based on other illnesses.

"No one has managed to do a longitudinal timeline that says what percentage of men carry Zika virus in their sperm for a week, two months, three months six months."

Therefore the time frame for safe sex was informed by an "abundance of caution".

"The Australians suggest three months [of safe sex on return home], the British six months. Can I point you out a paper that explains those differences? No. They are estimates based on best information and the experience of the clinicians."

Dr Jessamine said sexual transmission of the virus was "interesting" but remained rare -- there are only about 10 cases confirmed in medical literature. The main focus remained reducing infection from mosquito bites.

The World Health Organisation has said the virus has been reported in 61 countries and territories, mostly in Latin America and the Western Pacific region.

Most people who get the virus have no symptoms. Others may suffer from a mild and brief illness, but infections in pregnant women have been strongly linked to fetal deaths and to potentially devastating birth defects such as babies born with abnormally small heads.

That has been common in Brazil. The mosquitoes that are able to transmit Zika virus are not normally found in New Zealand. A national mosquito surveillance programme has been operating for some years at New Zealand's international points of entry.

The Ministry of Health recommends that women who are pregnant or plan to become pregnant in the near term consider delaying travel to areas with Zika virus present.

Ministry of Health advice relating to sexual transmission of Zika virus:

• All men who have travelled to a Zika-affected area and have a partner who is at risk of becoming pregnant should abstain from sexual activity (oral, vaginal and anal) or use condoms, whether they have symptoms or not, for at least six months after leaving a Zika-affected area.

• All men who have travelled to a Zika-affected area and have a pregnant partner should abstain from sexual activity (oral, vaginal and anal) or use condoms for the duration of the pregnancy, whether they have symptoms or not.

• Women who are pregnant or plan to become pregnant in the near term should consider delaying travel to areas with Zika virus present.

• There is only limited evidence available at this time about how long these men should abstain from sex or use condoms, and international advice varies.