A new report from Brazil raises questions about whether the Zika virus can continue to damage an infected infant’s brain after birth. An infant in Sao Paulo whose mother was infected late in

her second trimester was born without any visible birth defects. But testing showed the baby had the Zika virus in his blood; the virus remained in his system for at least a couple of

months. At six months, it became apparent that the child had suffered Zika-related brain damage. He had severe muscle contractions — a common sign of brain damage — on one side of his body.

A number of doctors from Sao Paulo reported the case in a letter published by the New England Journal of Medicine on Wednesday. Did the brain damage occur while he was in his mother’s womb?

virus could attack the brains of young children infected shortly after birth. Dr. Rita Driggers, the director of maternal fetal medicine at Sibley Memorial Hospital in Washington, said it’s

simply not known when the risk lessens or disappears. “At some point you’re not at risk like the fetus is. But we don’t know exactly at what age that is,” said Driggers, who was not an

author of the letter in NEJM. A spokesman for the Centers for Disease Prevention and Control said the issue is an important one to study. The spokesman, Tom Skinner, said in an email that

the CDC currently has no data that sheds light on these questions. But he suggested Zika pregnancy registries that the agency has set up — which will follow children born to women infected

in pregnancy — may help provide answers. In the Sao Paulo case, the mother developed symptoms of Zika when she was 26 weeks pregnant. It’s thought she contracted the virus sexually; her

husband was sick three weeks earlier. The baby appeared to be fine when it was born, though his head circumference was on the edge of being considered abnormally small. Blood, urine, and

saliva samples taken when the baby was 54 days old tested positive for traces of Zika virus, though he seemed healthy when examined. Blood drawn when he was 67 days old also tested positive.

At six months, however, the infant was showing signs of developmental problems. Dr. Deborah Levine, director of obstetrics and gynecological ultrasound at Boston’s Beth Israel Deaconess

Medical Center, said reports like this one help to flesh out the full picture of the risks posed by Zika infection. Levine and colleagues published a paper Tuesday in the journal Radiology

that reported on the cases of 45 infants with profound brain damage due to Zika infection. Levine’s specialty is high-risk obstetric ultrasound, so she has seen plenty of fetuses with brain

anomalies. But the damage she saw in these babies is “more severe than what I’m used to seeing.” In most of the cases, mothers had been infected in the first trimester of pregnancy, which is

believed to pose the highest risk. But Levine said scientists still need to better understand the nature of the consequences when Zika infections occur later in pregnancy. Doctors studying

the Zika outbreak in Brazil have warned for awhile that microcephaly — a condition in which the head is abnormally small — is just one of the problems associated with infection during

pregnancy, and that a range of harder to spot problems are also likely to be seen as time goes on. The case described in NEJM supports that warning. “What we can say is that an initial

examination that looks normal is reassuring,” Levine said. “But if it’s been a severe infection or a late infection, it makes a lot of sense to make sure that the babies get the appropriate

follow-up.”