Zika infection after birth causes brain damage in monkeys

Non-human primate model of Zika infection after birth offers clues to how brain is affected.

Findings have implications for monitoring Zika in young children, pediatric researcher says

Rhesus macaques infected with the Zika virus acted differently in behavioural stress tests compared with healthy animals. (Brennan Linsley/Associated Press)

Complications from the Zika virus in babies born to women who were infected during pregnancy are well known. Now researchers working with monkeys say infections after birth could also result in brain abnormalities. 

When the World Health Organization (WHO) declared Zika a global health emergency in 2016, much of the concern centred on how the virus can result in severe birth defects — such as underdeveloped brains — when pregnant women were infected. The virus spreads mainly by mosquitoes but can also be sexually transmitted.

In Wednesday's issue of the journal Science Translational Medicine, Dr. Ann Chahroudi of Emory University in Atlanta and her team say they found brain abnormalities during the first year of life in rhesus macaques that were infected with Zika after birth.

Scientists suspect the virus might harm brain development during the first year of life because the brain doubles in volume during this period. Based on what they've seen in infants who were exposed to the Zika virus in the womb, Chahroudi said they hypothesized that postnatal infection may also have adverse consequences for the central nervous system.

Dr. Angela Rocha shows brain scans of a baby born with microcephaly at the Oswaldo Cruz Hospital in Recife, Brazil, in 2016. New findings from monkeys suggest health authorities should closely monitor Zika infections in children and infants, and follow such cases over longer periods of time. (Felipe Dana/Associated Press)

"I would have a heightened level of concern for changes in brain development and behaviour based on our results," Chahroudi, a pediatric infectious disease physician, said in an email.

That's why the researchers now recommend more than just routine monitoring for pediatric patients known to be infected with Zika.

Chahroudi also expressed caution about extrapolating the results of a study on a relatively small number of infant macaques to human infants. 

To learn more, Chahroudi and her team infected six infant macaques with Zika five weeks after birth.  

After infection, the virus invaded the peripheral and central nervous systems, leading to abnormalities such as inflammation, an increase in astrocytes — a certain kind of star-shaped brain cell — and destruction of nearby neurons, as well as other damage.

The scientists also took MRI brain scans of the monkeys at three and six months of age to look for changes in anatomy and function in infected animals compared with two healthy, control animals.  

The scans pointed to changes in the brain's limbic system, which is involved in regulating emotion.

The neurological, behavioural and emotional differences lingered months after the virus cleared from the blood of the macaque infants, the researchers found. 

The scans also helped to confirm which brain regions areas are damaged by the virus or are harmed indirectly by inflammation, the study's authors said.

Infected monkeys also acted differently in behavioural stress tests compared with healthy monkeys, such as making abnormal calls when faced with a mild threat from a human intruder.  

The data suggest Zika infection after birth may disrupt how areas of the brain mature, which results in poor emotional processing, they said.

The results of animal studies often don't apply to humans. The U.S. National Institutes of Health recently funded a study of Guatemalan children infected with Zika after birth, the researchers said, which could shed more light for clinicians.

With files from CBC's Amina Zafar