Zika-caused birth defect may become clear only after birth

NEW YORK >> Researchers say a severe birth defect caused by Zika infection may not be apparent at birth but develop months afterward, further confirmation that the virus can cause unseen damage to developing babies.

The findings come from a study of 13 Brazilian babies whose heads all appeared normal at birth but then grew much more slowly than normal.

Most people infected with Zika never develop symptoms, but infection during pregnancy can cause devastating birth defects, including microcephaly, in which a baby’s skull is much smaller than expected because the brain hasn’t developed properly.

Microcephaly is diagnosed based on a measurement of the baby’s head circumference. It can be done during pregnancy using ultrasound, or after the baby is born. Doctors then compare the measurement to standard sizes of other kids, based on gender and age.

The study focused on 13 babies born in Brazil late last year and earlier this year. All had head heads that were a little small at birth, but within the normal range. Over the next five to 12 months, doctors noted their heads weren’t growing at normal rates. Eleven were eventually diagnosed with microcephaly.

Many of the children also developed other problems that have been linked to Zika, including epilepsy, problems swallowing, muscle weakness and inflexible joints.

Dr. Peter Salama, chief of emergencies at the World Health Organization, told reporters in Geneva on Tuesday that understanding of the complications from Zika continues to evolve. “We are also learning lot every day,” he said.

The Centers for Disease Control and Prevention released the findings Tuesday. The authors were a team of researchers from Brazil and the United States.

“This is certainly the first detailed description of these kinds of cases,” said Dr. Ganeshwaran Mochida, a pediatric neurologist at Boston Children’s Hospital.