It’s known that Zika can cause brain damage in the fetuses of infected pregnant women. Now a new study suggests the virus also may be able to harm the brains of some adults.

Scientists at the Rockefeller University and the La Jolla Institute for Allergy and Immunology infected adult mice with Zika and watched the virus zero in on and damage cells that are important in their brains to memory and learning, much in the same way researchers have documented how it attacks and kills cells critical to fetal brain development. The research was published Thursday in the journal Cell Stem Cell.

The authors of the study cautioned that it is difficult to know the extent to which the findings, in mice whose immune systems were weakened, apply to humans, and said they plan further research. But the findings clearly suggest that Zika may not be as benign an infection for adults—or even children—as currently thought, particularly for those with weakened immune systems, they said. Damage to these cells could potentially lead long-term to depression or other cognitive problems, they said.

“Zika has the potential to cause damage in the adult brain,” said Joseph Gleeson, adjunct professor and head of the laboratory of pediatric brain disease at New York’s Rockefeller University, and an author on the study.

The study delivers just the latest unsettling news about a virus that until very recently wasn’t thought to be terribly harmful. Over the past year, doctors and researchers have discovered the mosquito-borne virus can severely damage fetal brains. It can be spread sexually by men and women. There have also been other signs that the virus can harm adults: It has been linked to a rare neurological disorder, Guillain-Barre Syndrome. Scientists are exploring possible links with encephalitis, too.