Researchers at the Centers for Disease Control and Prevention have found that Zika virus infection can persist in a fetus's brain and/or a mother's placental tissue for nearly seven months after the mother's initial infection. Furthermore, the virus can continue replicating in the brain even after birth.
They tested placental tissues of 44 women who had been infected with Zika, half of whom delivered healthy babies and half had complications due to Zika (miscarriage, microcephaly, still birth, abortion). Brain tissues were also tested from 8 infants who were born with microcephaly and later passed away. All 8 of the infants' mothers had contracted Zika in the first trimester of pregnancy, which supports previous findings that Zika infection can be most harmful to the fetus early in a pregnancy. Overall, the CDC's findings help explain why Zika virus can cause such severe birth defects and complications in pregnancies.