Zika infection was once thought to be a relatively harmless infection. It is particularly feared for its effect on the unborn babies of pregnant women.

As more studies are being conducted on the effects of the mosquito-borne virus, researchers learn that adults can also experience unwanted health effects because of Zika infection such as Guillain-Barré syndrome (GBS), a sickness of the nervous system.

Now, Italian researchers report of another danger of Zika. In a letter published in the journal Emerging Infectious Diseases, the researchers reported that they have found evidence that Zika infection can affect the brains of adults and damage memory.

Emanuele Nicastri, from the National Institute for Infectious Diseases Lazzaro Spallanzani, and colleagues described the case of a 32-year-old nurse who was infected with Zika in the Dominican Republic.

More than a week after she returned from the Dominican Republic, the woman went to a clinic because of a set of symptoms that include rash, weakness and headache. She eventually had trouble walking and had to be hospitalized because of her neurological symptoms.

Tests eventually revealed that the woman had Zika. The virus was found in the woman's blood, saliva, urine and vagina, though she did not have sexual contact while in the Dominican Republic.

In an experiment published last month in Cell Stem Cell, researchers found that Zika virus can also affect adult brain cells in mice, which suggests that infection of the Zika virus is not as harmless for grown-ups as previously thought.

The nurse's case provided evidence that Zika virus can indeed affect the brains of human adults. The patient had early neurologic symptoms and suffered moderate memory impairment based on neuropsychological examinations, and these are consistent with symptoms of Zika virus-related encephalitis.

While the nurse made a full recovery after three weeks, the researchers said that her case highlights the need for doctors to be on the lookout for neurological symptoms in patients who are infected by the Zika virus.

"Our case highlights the potential for Zika virus neurotropism and the need for early identification of Zika virus-related neurologic symptoms. Moreover, the presence of Zika virus in the genital tract supports the recommendation of safe sex practice for women returning home from areas with ongoing Zika virus transmission," the researchers reported.

Although adults' brains are less vulnerable to damage compared with those of developing babies, brain damage may cause personality changes, epilepsy, depression and dementia.