What we know
- Pregnant women can be infected with Zika virus.
- The primary way that pregnant women get Zika virus is through the bite of an infected mosquito.
- Zika virus can be spread by a man to his sex partners.
- A pregnant woman can pass Zika virus to her fetus.
- Zika virus can be passed from a pregnant woman to her fetus during pregnancy or at delivery.
What we do not know
- If a pregnant woman is exposed
- We don’t know how likely she is to get Zika.
- If a pregnant woman is infected
- We don’t know how the virus will affect her or her pregnancy.
- We don’t know how likely it is that Zika will pass to her fetus.
- We don’t know if the fetus is infected, if the fetus will develop birth defects.
- We don’t know when in pregnancy the infection might cause harm to the fetus.
- We don’t know whether her baby will have birth defects.
- We don’t know if sexual transmission of Zika virus poses a different risk of birth defects than mosquito-borne transmission.
Zika and microcephaly
Since May 2015, Brazil has experienced a significant outbreak of Zika virus. In recent months, Brazilian officials reported an increase in the number of babies born with microcephaly.
Since these initial reports of a link between Zika and microcephaly, researchers across the world began working to study the link between Zika during pregnancy and microcephaly. In a recent article, CDC scientists announced that there is now enough evidence to conclude that Zika virus infection during pregnancy is a cause of microcephaly and other severe fetal brain defects and has been linked to problems in infants, including eye defects, hearing loss, and impaired growth. Scientists are studying the full range of other potential health problems that Zika virus infection during pregnancy may cause.
Other possible causes of microcephaly
Microcephaly can happen for many reasons. Some babies have microcephaly because of
- Changes in their genes
- Certain infections during pregnancy
- A woman being close to or touching toxins during pregnancy
Recent media reports have suggested that a pesticide called pyriproxyfen might be linked with microcephaly. Pyriproxyfen has been approved for the control of disease-carrying mosquitoes by the World Health Organization. Pyriproxyfen is a registered pesticide in Brazil and other countries, it has been used for decades, and it has not been linked with microcephaly. In addition, exposure to pyriproxyfen would not explain recent study results showing the presence of Zika virus in the brains of babies born with microcephaly.
Zika and Other Birth Outcomes
In addition to microcephaly, other problems have been detected among fetuses and infants infected with Zika virus before birth, such as eye defects, hearing loss, and impaired growth. Although Zika virus is a cause of microcephaly and other severe fetal brain defects and has been linked with these other problems in infants, there is more to learn. Researchers are collecting data to better understand the extent Zika virus’ impact on mothers and their children.
Based on the available evidence, we think that Zika virus infection in a woman who is not pregnant would not pose a risk for birth defects in future pregnancies after the virus has cleared from her blood. From what we know about similar infections, once a person has been infected with Zika virus, he or she is likely to be protected from a future Zika infection.