(CNN) If you're a man who travels to an area with active Zika transmission, you should wait at least six months after exposure to have unprotected sex or try to conceive a baby, the Centers for Disease Control and Prevention announced Friday, even if you never had symptoms of the virus. Women should wait a full eight weeks after exposure.

"The time frames now match, whether you are trying to prevent sexual transmission or protect pregnancy," said Dr. Denise Jamieson, chief of the CDC's Women's Health and Fertility Branch. "We are making it simple."

The World Health Organization issued similar guidelines in early September, but its advice went further, recommending that women as well as men wait a full six months to conceive a baby or practice unprotected sex.

The updated advice follows numerous case reports showing Zika may hide in semen for up to six months after symptoms begin, which typically include fever, rash, achy joints and muscles and red eyes similar to conjunctivitis.

And then there was the man who gave Zika to his female partner when he didn't even know that he had it, proving that even people with no symptoms can still be infectious.

"I think that case is very important," said Dr. John Brooks, a medical epidemiologist with the CDC, "because it reminds us that even though it might be less common than transmission from a person with active signs of Zika, it can still occur."

This is the fifth time the CDC has updated its Zika guidance for pregnancy and the fourth update on the prevention of sexual transmission since Zika became a public health concern, a sign of how quickly information about Zika and its long-term effects can change.

Zika is now widespread

Zika is just starting to spread throughout Southeast Asia and is spreading through local transmission in at least 60 countries and territories around the world, including the Miami-Dade area of Florida.

The best advice to protect yourself and your sexual partner: Don't travel to those areas. But if you both live there or must travel for work, protection from mosquito bites is a must.

Unfortunately, if your protection fails, you'll probably never feel the bite that could give you Zika. That's because the female mosquito that transmits Zika, the aedes aegypti, is so small her nip is almost painless.

And because only one out of every five infected people has symptoms, that means you can't be absolutely sure that you -- or your sexual partner -- didn't get the virus. Which means you can't be 100% sure that you won't get the virus from sex.

Pregnant women and their partners

Pregnancy is the most dangerous time to catch the Zika virus. It's been linked to devastating neurological birth defects that destroy developing brain cells in the fetus, leading to a condition called microcephaly, which means "small head." Babies with this disorder, if they live, often have seizures and difficulty lifting their heads, controlling their muscles or even feeding. The impact is lifelong, and care is expensive: The March of Dimes recently estimated the lifetime cost for one child with microcephaly at over $10 million.

But even if the baby escapes microcephaly, Zika has been known to cause brain calcifications, vision and hearing problems, and learning disabilities. Researchers are scrambling to find out just how widespread the damage can be.

Because of this danger, several South and Central American countries are encouraging their citizens to delay pregnancy until the outbreak is over, if possible.

The WHO and the CDC have not gone that far. Instead, they recommend pregnant women avoid travel to any areas where Zika is circulating. If that is absolutely unavoidable or you live in a Zika-infested area, use all known precautions to avoid a bite . And be sure to check in with your health care provider for Zika testing and careful monitoring.

If a pregnant woman's partner is the traveler, safe-sex precautions should be carefully and properly used for every sex act throughout the entire pregnancy, or sex should be avoided . That precaution applies to both male and female partners of the pregnant woman and includes male and female condoms, sex toys and dental dams for any vaginal, anal or oral sex.

Couples trying to conceive

If you and your partner are actively trying to conceive, you also need to take significant precautions. Because women can be pregnant for several weeks before they know it, it's best to avoid travel to Zika-infested areas.

"If you're a couple and traveling to these areas," said Brooks, "while you're there, we recommend you consider using condoms, as you don't know which of you might be bitten and transmit the disease."

"For most people, that's the time they depart the area of risk," Brooks said. "For others, it may be the last time they had a sexual exposure to someone."

Regardless, the practice of safe oral, anal and vaginal sex should continue for a full eight weeks if you're a woman, and six months if you're a man, according to the CDC.

That's based on existing data. With Zika, things change frequently.

"Given that limited data are available," said the CDC guidance, "some couples in which a partner had possible Zika virus exposure might choose to wait longer or shorter than the recommended time period to conceive, depending on individual circumstances (maternal age, fertility, details of possible exposure) and risk tolerance."

Not making a baby anytime soon?

If you and your sexual partner have no plans for babies anytime soon, does that mean you're off the hook? Not if you're a good citizen.

That's because every person who brings the virus back into their country and gets bitten by an Aedes aegypti mosquito could be starting a local outbreak, which is what is happening now in Southeast Asia and in Florida in the United States. That's why returning travelers from areas where the virus is circulating are advised to use mosquito repellant for the first three months they are home.

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So taking precautions to "avoid the bite" when you return is good for the community and the many pregnant women who are living happily around you, unaware that you could be soon turning their safe zone into a new Zika hot zone.

Next, according to the CDC, after any exposure to Zika, you should continue to practice safe oral, anal and vagina sex for at least six months if you're a man and eight weeks if you're a woman. That's to make absolutely sure that you don't infect your unborn fetus in case your birth control method fails. After all, no method is 100% effective, and there is always a risk of exposure before the woman misses her menses.

"The primary focus is on protecting pregnant women and women trying to conceive," said Jamieson. "All men should wait six months after exposure to attempt conception with their partner or practice unprotected sex."