Zika virus may have damaged more infants’ brains than previously thought, research suggests

Sizeable number of infants born with normal-sized heads later had neurological development problems

Children exposed to Zika virus during pregnancy should be monitored more closely, experts have warned, after a study suggested that the infection damaged more infants’ brains than previously thought.

Researchers initially established that babies born with small heads (microcephaly) went on to develop neurological or developmental problems, while infants born with normal head circumference (normocephalic) were thought to be at low risk.

But a new study, looking at infants born during Latin America’s Zika epidemic in 2015/16, suggests that a large number of children born with normal-sized heads had not developed properly at follow-up examinations.

“Unfortunately what we are seeing at follow-up is that a sizeable number of children have neurologic abnormalities when followed over time,” said Dr. Sarah Mulkey, director of fetal, transitional and neonatal neurology fellowship at Children’s National Hospital in Washington.

“The 68 per cent seen in this cohort is very high, and relates to why the mother and infants were referred for evaluation in this program, but even among a general cohort of children with utero Zika exposure...we do see that these ‘normal-appearing’ children can have decreased neurodevelopmental skills.”

The study, published in JAMA Network Open, included data on nearly 300 infants in Brazil with known (74 per cent) or suspected Zika infections acquired during pregnancy.

Of those children examined in the research, 24 per cent were born with microcephaly while the rest appeared to have normally developed heads.

“This new report is concerning, as it shows that, with longer follow up, more babies are found to be affected than we had hoped,” said Jimmy Withworth, professor of international public health at the London School of Hygiene and Tropical Medicine.

“Because of the study design it is not possible to accurately determine what proportion of all the Zika-exposed babies are affected.

“It also shows that head circumference at birth, even within the normal range, is an important prognostic indicator of risk of failure to develop.”

The World Health Organisation (WHO) in 2016 described the Zika outbreak in South America as having potentially “explosive pandemic potential”, declaring a global public health emergency on 1 February.

Authorities there have since brought the infection under control and there have been no recent cases in the UK. Medics in Ireland recently recorded a case in Dublin in a woman who had been living in her native Brazil during the epidemic.

Zika virus is a mosquito-borne disease that normally has symptoms similar to the dengue and chikungunya viruses, which are spread by the same genus of insect. It is transmitted to humans by the bite of infected Aedes mosquitos, which also carry dengue, chikungunya and yellow fever.