Since an outbreak in Brazil in 2015 grabbed headlines around the world, the Zika virus has affected many infants who were born with microcephaly. However, a new animal study led by researchers from the University of Washington School of Medicine in Seattle has found that the Zika virus may damage fetal brains even when the baby's head is normal, according to a recent report by Science Daily.

The study, published in the Feb. 5 issue of Nature Medicine, involved the analysis of subtle changes in the brains of five fetal macaques whose mothers has been infected with the Zika virus while pregnant.

"Current criteria using head size to diagnose Zika-related brain injury fail to capture more subtle brain damage that can lead to significant learning problems and mental health disorders later in life," said author Kristina Adams Waldorf, MD, a professor of obstetrics and gynecology at the UW School of Medicine who specializes in maternal and fetal infections, to Science Daily. "We are diagnosing only the tip of the iceberg."

Some brain MRI may have difficulty detecting damage that can occur in children infected during early childhood and adolescence. MRI results showed that four of the five animals had abnormalities with certain areas of the brain not developing as quickly as others.

"The study clearly shows that cells within these brain regions are highly susceptible to Zika virus infection. The findings suggest that neural stem cells within these sites, and at specific stages of development, are unable to suppress virus replication," Waldorf said.