As mosquito season in the United States approaches, we've been hearing stories of pregnant women anxiously emailing each other about how to Zika-proof their lives. Some are cancelling trips to Brazil or Florida because of fears of the virus.
It's no wonder: While Zika seems to be pretty benign in most people, not even causing symptoms in about half of those infected, it's extremely harmful to fetuses.
The Centers for Disease Control and Prevention recently declared that there's indisputable evidence that Zika can cause a devastating birth defect called microcephaly, which is characterized by a shrunken head and incomplete brain development.
In addition to microcephaly, researchers have found that the virus seems to kill off the tissue in entire regions of the brain, damage babies' eyes, and heighten a woman's risk of miscarriage and fetal death.
To find out more about the true risks to women here in the US, we talked to Dr. Denise Jamieson, an obstetrician-gynecologist and the chief of CDC's women's health and fertility branch. She is currently leading the pregnancy and birth defects task force for the agency's Zika response.
Her message is clear: The immediate risks of Zika are only for women living in places where the virus is currently transmitting, like Brazil, Colombia, and the Caribbean. Mosquitoes are not spreading the disease in the continental US — so far, all cases here have only been tied to travel or sexual transmission.
That said, Jamieson says there are still plenty of precautions women — and anyone else — can take to protect against mosquitoes.
Julia Belluz: About a month ago, the CDC said Zika outbreaks here in the US would probably be quite limited, if we had any at all. Has that assessment changed?
Denise Jamieson: The CDC is really not able to predict how much Zika might spread in the continental US, and many areas here have the kind of mosquitoes (Aedes aegypti) that can be infected with and spread the Zika virus disease.
But we saw other recent outbreaks [in the US] of other diseases — chikungunya and dengue viruses — spread by the same type of mosquito, and those outbreaks were small and limited to one small area. We are not sure what to expect but we are hoping that a Zika outbreak would look similar to the other outbreaks.
JB: If we do see a Zika outbreak here, how exactly would they start?
DJ: In order for Zika to cause an outbreak, people infected with the virus have to enter the US, and Aedes aegypti mosquitoes in the US would have to bite that infected person during the time virus can be found in person's blood, which is a short period of time (about a week).
Those mosquitoes have to live long enough for virus to multiply, and for the mosquito to bite another person. That cycle would have to be repeated several times in order to have an outbreak in continental US. So a lot of things that need to happen.
JB: OK, so that helps explain why widespread outbreaks aren't that likely. Still, there's a lot of concern about the virus because of the link between Zika and microcephaly, which was recently verified by your agency. What else do we know about how the virus affects fetuses?
DJ: What we know is that Zika causes microcephaly and other severe brain abnormalities. What we don't know is what the spectrum of possible effects are. We don't know if this is just the tip of the iceberg, and there are many other effects we're not seeing. The other piece we don't know is how often these effects occur. We know there have been pregnant women who have been infected with Zika and have had healthy babies.
To find out more, we're following infants born to pregnant women who were infected with Zika — both the babies born with microcephaly and babies born healthy — in the US Zika Pregnancy Registry to see if there are other effects we're not seeing.
JB: The virus seems to generally be harmless to adults. Why is it so harmful to fetuses?
DJ: The emerging evidence suggests the period of greatest risk for fetuses is during the first trimester of pregnancy. It's in that period when all the organ systems are forming. And when the brain is forming, we believe the virus can have detrimental effects.
This is very different than what happens in adults. In general, Zika is either asymptomatic or a mild disease in most people. We need to know more but what we know now is that we don't have any evidence that Zika is more severe in infants or children who are infected. So for most people, Zika virus infection is a mild disease, and that's why our prevention efforts have focused on protecting pregnant women.
JB: How should women in the continental US think about the Zika risk as mosquito season approaches?
DJ: Although the mosquitoes that carry Zika are here, Zika is not currently here. We are advising pregnant women in the continental US to avoid travel to areas where there is ongoing Zika transmission. (This includes more than 40 countries in South and Central America, the Pacific Islands and the Caribbean.)
For women who live here and are pregnant — they should avoid mosquito bites.
JB: What do you suggest for avoiding mosquito bites?
DJ: Use EPA-registered insect repellents, wear long sleeves, treat clothing with permethrin (an insecticide), and stay in places with air conditioners and screens on the windows and doors.
That advice applies to all people everywhere but it's particularly important for pregnant women living in areas of active Zika transmission. Avoiding having standing water (where mosquitoes can breed and grow) in and around the home is also important. The other way you can get Zika is from sexual transmission.
JB: Some women may be concerned about using mosquito repellent while pregnant. What advice do you have for them?
DJ: EPA-approved insect repellents, if used according to package instructions, are safe for pregnant women and pregnant women should be using them — the risk of not using them is substantial.
JB: Do you have any advice for women who are thinking about getting pregnant in the near future?
DJ: For women who have been infected with Zika or who travel to areas with ongoing Zika transmission, we are recommending they wait eight weeks until they get pregnant. That's because that's when the virus is still in the blood, and we are concerned that there could be harmful effects on the pregnancy.
For men, it's different: If they had Zika, they should wait six months (before having unprotected sex) because the virus can live longer in the semen. (Read more about why here.)