Zika can “wreak havoc” on the brains of adults and cause major, lasting damage, according to a new study. The research could overthrow the assumption that the virus is only of major worry to pregnant women.

Until now, the mosquito-borne infection has been primarily linked to microcephaly, a serious defect where babies are born with small heads and brain damage. That has mean that pregnant women were warned to avoid coming into contact with the infection – but others have shown no obvious symptoms.

But a major new study on mice indicates that the impact of the Zika infection in other adults could be far more serious and sinister than had previously been thought.

Experiments on adult mice engineered to mimic human Zika infection show that the virus seems to attack immature cells in the adult brain. Those same cells are vital to learning and memory – and so losing them could have disastrous effects, comparable to those experienced by people with Alzheimer’s.

Battling the zika virus - in pictures Show all 19 1 /19 Battling the zika virus - in pictures Battling the zika virus - in pictures A worker of the Salvadorean Ministry of Health fumigates a house in Soyapango, 6 kilometers from San Salvador, El Salvador. Salvadorean authorities have began a three days campaign of fumigation to reduce the presence of the mosquito that transmit the Zika virus. EPA/Oscar Rivera Battling the zika virus - in pictures A Health Ministry employee fumigates a home against the Aedes aegypti mosquito to prevent the spread of the Zika virus in Soyapango, six km east of San Salvador. Health authorities have issued a national alert against the Aedes Aegypti mosquito, because of the link between the Zika virus and microcephaly and Guillain-BarrÈ Syndrome in foetuses. AFP PHOTO/Marvin RECINOSMarvin RECINOS/AFP/Getty Images Battling the zika virus - in pictures A pediatric infectologist examines a two-months-old baby, who has microcephaly, on 26 January 2016 in Recife, Brazil. Getty Images Battling the zika virus - in pictures A woman walks through the fumes as Health Ministry employee fumigate against the Aedes aegypti mosquito to prevent the spread of the Zika virus in Soyapango. Marvin RECINOS/AFP/Getty Images Battling the zika virus - in pictures A health ministry employee sprays to eliminate breeding sites of the Aedes Aegypti mosquito, which transmits diseases such as the dengue, chicunguna and Zica viruses, in a Tegucigalpa cemetery on January 21, 2016. The medical school at the National Autonomous University of Honduras (UNAH) recommended that women in the country avoid getting pregnant for the time being due to the presence of the Zika virus. If a pregnant woman is infected by the virus, the baby could be born with microcephaly. AFP PHOTO/Orlando SIERRA Battling the zika virus - in pictures A man walks away from his home with his son as health workers fumigates the Altos del Cerro neighbourhood as part of preventive measures against the Zika virus and other mosquito-borne diseases in Soyapango, El Salvador REUTERS/Jose Cabezas Battling the zika virus - in pictures A three-months-old, who has microcephaly, in Recife, Brazil. Getty Images Battling the zika virus - in pictures A pregnant woman waits to be attended at the Maternal and Children's Hospital in Tegucigalpa. The medical school at the National Autonomous University of Honduras (UNAH) recommended that women in the country avoid getting pregnant for the time being due to the presence of the Zika virus. If a pregnant woman is infected by the virus, the baby could be born with microcephaly. ORLANDO SIERRA/AFP/Getty Images Battling the zika virus - in pictures Army soldiers apply insect repellent as they prepare for a clean up operation against the Aedes aegypti mosquito, which is a vector for transmitting the Zika virus in Sao Paulo, Brazil. AP Photo/Andre Penner Battling the zika virus - in pictures Workers disinfect the Sambadrome in Rio de Janeiro to fight the spread of the Zika virus Battling the zika virus - in pictures Dr. Vanessa Van Der Linden, the neuro-pediatrician who first recognized the microcephaly crisis in Brazil, measures the head of a 2-month-old baby with microcephaly in Recife Battling the zika virus - in pictures Mother Mylene Helena Ferreira cares for her son David Henrique Ferreira, 5 months, who has microcephaly, on January 25, 2016 in Recife, Brazil. In the last four months, authorities have recorded close to 4,000 cases in Brazil in which the mosquito-borne Zika virus may have led to microcephaly in infants Getty Images Battling the zika virus - in pictures U.S. women who are pregnant from traveling to many South American countries Battling the zika virus - in pictures In the last four months, authorities have recorded close to 4,000 cases in Brazil in which the mosquito-borne Zika virus may have led to microcephaly in infants. Getty Images Battling the zika virus - in pictures Dr. Vanessa Van Der Linden, the neuro-pediatrician who first recognized the microcephaly crisis in Brazil, examines a two-month-old baby with microcephaly on January 27, 2016 in Recife, Brazil Battling the zika virus - in pictures Washington Post Battling the zika virus - in pictures Battling the zika virus - in pictures Battling the zika virus - in pictures

Over time, the gradual attack on those cells could lead to shrinkage of the brain and major impairment of cognitive processes, the scientist behind the study said.

Professor Sujan Shresta, a member of the team from the La Jolla Institute of Allergy and Immunology in California, USA, said: "Zika can clearly enter the brain of adults and can wreak havoc. But it's a complex disease - it's catastrophic for early brain development, yet the majority of adults who are infected with Zika rarely show detectable symptoms.

"Its effect on the adult brain may be more subtle, and now we know what to look for."

The study is the first to look at the way that Zika attacks the adult brain. It was carried out by using fluorescent biomarker “tags” that could indicate where in the brain was invaded by the virus.

The scientists saw those attacks taking place in parts of the brain that are central to learning and memory, they write in the study published in the journal Cell Stem Cell.

Professor Joseph Gleeson, from Rockefeller University, said: "Our results are pretty dramatic - in the parts of the brain that lit up, it was like a Christmas tree.

"It was very clear that the virus wasn't affecting the whole brain evenly, like people are seeing in the foetus. In the adult, it's only these two populations that are very specific to the stem cells that are affected by virus. These cells are special, and somehow very susceptible to the infection.

"Based on our findings, getting infected with Zika as an adult may not be as innocuous as people think."

Healthy people might be able to resist those attacks. But people who already have weakened immune systems could be at risk.

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"In more subtle cases, the virus could theoretically impact long-term memory or risk of depression, but tools do not exist to test the long-term effects of Zika on adult stem cell populations,” said Professor Gleeson.

The scientists still aren’t sure the extent to which the behaviour in mice could apply to humans, or how permanent any damage sustained as a result of the virus might be. But they say that further work must be done to find out if Zika could cause long term mental impairment in adults.