Zika was long considered a fairly benign mosquito-borne virus. It didn't harm most of the people it infected, and those who did show symptoms only seemed to experience something like a flu.
After a massive outbreak started in Brazil last year, however, scientists are exploring a new version of Zika. There's evidence that the virus may pose a unique risk to fetuses if passed on through the mother. Specifically, Zika has been linked to a terrible birth defect called microcephaly, which causes babies' heads and brains to stop growing to full size.
Researchers are also learning that Zika may be spread through sexual intercourse — not only mosquitoes — and maybe even through other bodily fluids like saliva and urine.
These possibilities, and a shortage of clear answers, have put pregnant women in a very difficult place. They've been the subject of all kinds of advisories and warnings, even sparking heated debates about access to birth control and abortion.
There's still a lot researchers have to learn about Zika, especially its link with birth defects. For now, here are nine facts to know if you're pregnant and worried about this virus.
1) Pregnant women should consider postponing travel to countries with Zika
The Centers for Disease Control and Prevention (CDC) issued a first-of-its kind travel advisory about Zika, asking pregnant women to consider postponing their visits to places where the virus is circulating. This is very simply because of the potential birth complications the virus may bring. The link with Zika and birth defects hasn't yet been definitively proven (more on that in point 9), but right now there's no treatment or vaccine for Zika, so the only way pregnant women can stay safe is to avoid exposure to the virus.
The list of places with Zika has been growing by the week. So far, it includes more than 30 countries and territories in Central and South America and the Caribbean, including Brazil, Barbados, Colombia, Mexico, Puerto Rico, and the US Virgin Islands, as well as Cape Verde in Africa and the Pacific Islands.
For women who are thinking of becoming pregnant soon, the CDC recommends consulting your doctor before traveling to these countries and following steps to prevent mosquito bites during the trip.
2) If you're pregnant and visited a country with Zika recently, get tested
The CDC now advises all pregnant women who have recently traveled in a country where Zika is circulating to see their doctor and get tested for the virus — regardless of whether they have symptoms. All tests should also be followed up with ultrasounds later on.
Meanwhile, if you live in a place with Zika transmission, make sure you're taking precautions to avoid mosquito bites (more in point 6 below) and that you're under the care of a physician. The CDC recommends seeing your doctor to get checked for symptoms of Zika and to get tested for the virus. (Details here.)
3) Right now the tests for Zika aren't perfect
Unfortunately, Zika tests don't always deliver clear answers. Tests that look for the virus itself only work for about a week after infection, so if you were infected several weeks before testing, you may get a result anyway. Indirect tests that check for antibodies can be done at any time — but they might lead to false positives in women who have had similar viruses (including dengue or yellow fever).
That's why the CDC recommends that pregnant women get ultrasounds to look for microcephaly, regardless of the test outcome. Here, too, there are some complexities. Researchers believe that fetuses at the earliest stages of development are most at risk of complications — but ultrasounds usually can't detect microcephaly until near the third trimester. Some women are advised to consider amniocentesis after 15 weeks of gestation, but these tests carry their own risks, including miscarriage.
Again, all this puts women in a very difficult position, which is part of the reason why improving testing for Zika is a top priority right now. It's also why the CDC is telling pregnant women to simply avoid places where the virus is circulating.
4) Zika clears from the body in about 10 days
If you're recently pregnant and worried about a trip you took a long time ago to an area with Zika transmission, there's no cause for concern. The virus clears from the blood within 10 days, and there's no evidence that Zika affects future pregnancies once it's gone.
That means that if a fetus is conceived several weeks, months, or years after a mother is exposed to the virus, there shouldn't be a risk of potential birth complications from Zika.
5) Zika is mainly spread by mosquitoes — but only certain types
There are many different types of mosquitoes, but Zika is mainly carried by a specific kind called the Aedes aegypti. These mosquitoes, which bite during the day, can also transmit dengue, yellow fever, and chikungunya viruses. (There's some evidence that the Asian tiger mosquito — Aedes albopictus — can transmit the virus, too, though the Aedes aegypti is still thought to be Zika's primary carrier.)
These mosquitoes are mostly found in the southern US. If you live in an area with this type of mosquito, as well as evidence of a Zika outbreak, you should probably consider taking extra precautions to avoid bites. If you don't, you shouldn't have much to worry about. Unfortunately, it's women in Latin America — where the mosquito is common and there's local transmission of the virus — that are currently the most at risk.
6) There are easy precautions to avoid mosquito bites
Since Aedes mosquitoes prefer small bodies of water around people's homes, there are important and effective measures that individuals can take to limit mosquitoes' habitats, says Janet McAllister, a researcher in the division of vector-borne diseases at CDC.
"Just generally keeping your yard clean and in shape, getting rid of debris or things stored outside that can hold water, or adjusting them so that they no longer hold water," McAllister says. "It's also important to maintain the vegetation in your yard — to keep the grass mowed and bushes trimmed, with good air flow." Campaigns to clean up people's yards and work sites, and instituting tire pickup programs (old tires are a popular breeding place), can help eliminate mosquito breeding grounds.
Inside the home, the CDC recommends making sure you have screens on windows and doors that aren't punctured in any way. Wearing protective clothing, using insect repellents, and keeping your house cool with air conditioning also helps.
7) You can use insect repellent safely during pregnancy
Using insect repellent is safe — even for pregnant women. The CDC just advises women who are pregnant or breastfeeding to choose an EPA-registered insect repellent and use it according to the product label.
8) Zika can also be sexually transmitted
Sexual transmission is thought to be a rare but plausible route for spreading Zika. In particular, men seem to be able to spread the virus through intercourse to women. This means it's important for pregnant women to practice safe sex during a Zika outbreak.
The CDC issued interim guidance on safe sex and Zika, suggesting men who have traveled in Zika countries and have female partners who are pregnant either avoid sex or use condoms for vaginal, anal, and oral sex for the duration of the pregnancy. (For couples who aren't pregnant, the CDC recommends considering condoms or abstaining if the male has traveled in a place with Zika.)
There's a lot of uncertainty about this risk. Researchers aren't sure how long Zika can remain in semen, when people are most at risk of passing on the virus, or what types of sex acts are more likely to spread the virus. Again, sexual transmission is also thought to spread only from men to women (not vice versa) — but that information might change as we learn about more cases.
To date, there have only been a few cases in the medical literature that suggest Zika can be sexually transmitted. In one case, a man who traveled to Senegal in 2008 and contracted Zika gave it to his wife through intercourse after he returned home to Colorado. In another, Zika was isolated from semen. The first case of sexual transmission during the current outbreak in the US was documented in Dallas in February: A traveler returned from Venezuela, where the virus was circulating, and infected his partner.
9) Researchers still aren't clear on the precise risk Zika poses to fetuses
One of the things that makes Zika very difficult to track is the fact that in the vast majority of cases, it causes no symptoms at all. Most people who get infected don't even realize it — and therefore never seek medical attention. They can, however, still transmit the disease if they are bitten by a mosquito that then bites someone else.
Meanwhile, a minority of Zika patients — roughly 20 percent — show relatively minor symptoms: a low-grade fever, sore body, and headache, as well as red eyes and a body rash. More rarely, this might include abdominal pain, nausea, and diarrhea. These symptoms usually appear two to 12 days after a bite and go away within a week.
Yet there is also evidence that Zika is linked to microcephaly, which is characterized by a shrunken head and incomplete brain development. (You can read more about microcephaly in our explainer here.) Since Zika arrived in Brazil in 2015, more than 4,000 suspected cases of microcephaly have been reported — a twentyfold increase from previous years.
The timing appears to be no coincidence. The Zika virus has been found in the amniotic fluid of pregnant women carrying babies with the birth defect, and even in the brains of babies with microcephaly who died within 24 hours of being born.
But there are also a lot of question marks here. Researchers are still working to confirm the link, checking to make sure there's not something else that's causing the microcephaly or that it's not just a measuring error. There are major questions about the frequency of the condition. It doesn't seem like every pregnant person infected with the virus then has a child with microcephaly, but how often birth complications arise is still unknown.
The health ministry in Brazil is currently going through suspected cases to make sure they're real, and so far they're discarding more than they're confirming. As of February 2, of the 4,783 suspected cases of microcephaly, 404 have so far been confirmed and 709 thrown out. Only 17 of the confirmed cases have been linked to Zika so far.
Still, Zika wouldn't be the first virus to cause microcephaly. Rubella famously caused an epidemic of birth defects before the advent of the vaccine. And the imperfect evidence about Zika and birth defects was enough to prompt the World Health Organization to declare a rare global public health emergency.
Expect all this information to keep changing
All this uncertainty certainly isn't reassuring. But it's also not entirely unexpected: This is a relatively new virus to humans, in that it hardly affected people or caused big outbreaks until very recently. Scientists are just beginning to understand what Zika can do.
So expect information about Zika — how it's transmitted, which mosquitoes can carry the virus, how it affects people — to change in the coming days and weeks. And keep checking the CDC's webpage on Zika for updates on pregnancy and travel.