The recommendation, which doubles the abstinence period the WHO had previously advised, comes after scientists found the virus lingers longer than previously thought in blood or other body fluids, spokesman Christian Lindmeier told a news briefing.

If the male partner in a couple planning pregnancy has symptoms of the Zika virus, the period of safe abstinence should be six months, he added.

"People should practise safer sex or abstain for at least eight weeks if they are returning from Zika-affected areas," he said. "The previous recommendation suggested a period of at least four weeks, so we're upping (it)."

The new guidelines "reflect what we have learned about Zika disease and its complications," he added.

Asked if this new advice amounted to an effective ban on pregnancies in Brazil, where the virus first appeared a year ago, Lindmeier said: "The guidance is to delay or consider delaying pregnancy, certainly recognising that this is tough for some populations."

The spokesman said scientists are still investigating how long the virus can be traced in saliva but these tests have so far been inconclusive.

"All this is being studied to see where else we find the virus and how long it sustains there," he said.