Scans have revealed a range of serious brain abnormalities in babies born with microcephaly, probably due to Zika exposure, says a study published in The BMJ. The findings emerge just days after Dr. Anne Schuchat, of the US Centers for Disease Control and Prevention, described the virus at a White House press conference as “scarier than we initially thought.”

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Zika has affected thousands of infants in Brazil.
Image credit: The BMJ 2015

The virus has emerged in several locations, particularly the densely populated cities of tropical and subtropical regions.

Since 2015, Zika has been linked with a dramatic rise in the prevalence of microcephaly in Brazil. Microcephaly is a rare birth defect in which babies are born with an abnormally small head.

Scientists have been trying to establish whether and how exposure to the virus before birth can lead to microcephaly.

Evidence of an association includes the simultaneous rise in the number of cases of microcephaly, as Zika has spread.

Researchers have identified the Zika virus genome in amniotic fluid samples from two pregnant women whose unborn babies had microcephaly and in the blood and tissue samples of a newborn baby with microcephaly who died 5 minutes after birth.

Animal experiments have indicated that Zika can damage or kill neural cells.

Finally, ultrasound scans have revealed a higher frequency of abnormalities among infants born to women with the Zika virus infection, compared with babies born to mothers without exposure.

In March 2016, the World Health Organization (WHO) concluded that there is strong scientific consensus supporting the link between the Zika virus and microcephaly.

Fast facts about Zika virus
  • As of April 6, 2016, the CDC reported 346 travel-related cases of Zika virus in the US
  • None were locally acquired vector-borne cases
  • 32 patients were pregnant women.

Learn more about Zika virus

Researchers in Recife, the Brazilian city at the center of the crisis, have used computed tomography (CT) and magnetic resonance imaging (MRI) to investigate the types of abnormalities and lesions in the earliest cases of microcephaly linked to the Zika virus.

Led by Prof. Maria de Fatima Vasco Aragao, they distinguished abnormalities seen in babies with microcephaly from those stemming from other congenital infections.

The doctors studied 23 babies diagnosed with a congenital infection associated with the Zika virus.

The infants, who were born in Pernambuco state, Brazil, from July-December 2015, all had either microcephaly or craniofacial disproportion in the womb or at birth. All but one of the mothers experienced a rash during pregnancy, implying exposure to Zika.

Six babies had Zika-related antibodies, and the other 17 met the criteria for microcephaly.

The researchers ruled out other risk factors for microcephaly, such as HIV, toxoplasmosis, syphilis, cytomegalovirus and rubella.

Fifteen of the babies had a CT scan, seven underwent CT and MRI, and one had only an MRI.

The scans revealed “extremely severe” brain damage in most of the babies that was likely to lead to impaired neurological function.

The CT scans revealed signs of brain calcification in all 22 children. Calcium is thought to accumulate on scar-like lesions where the Zika virus destroys brain cells. Calcium was prevalent in the junctions between cortical and subcortical white matter.

There were signs of cortical malformation in 95% of the babies, 91% had low brain volume and 86% had ventriculomegaly, or abnormal enlargement of the brain cavities.

Around half showed signs of hypoplasia, or underdevelopment, of the cerebellum or brainstem. The cerebellum plays a key role in motor control, and the brainstem connects the cerebrum with the spinal cord and communicates messages from the brain to the rest of the body.

The MRI scans also revealed calcifications and ventriculomegaly.

Seven out of 8, or 88%, had an enlarged cistern magna, probably because of reduced brain volume.

Delayed myelination was present in 88% of cases. Myelination is the process of a myelin sheath forming around nerve fibers. It enables transmission of impulses.

Six of the infants, or 75%, had a moderate to severe decrease in brain volume, 38% had a simplified gyral pattern, or hypogenesis, and 38% presented with abnormalities of the corpus callosum.

There were also abnormalities of the corpus callosum, the thick band of nerve fibers connecting the two sides of the brain that is involved in communication.

Malformations were symmetrical in 75% of cases.

The authors point out that the study, being observational, does not prove definitively that Zika causes the brain abnormalities.

However, they add:

“This study shows the largest and most detailed case series of neuroimaging findings in children with microcephaly and presumed Zika virus-related infection to date.”

A recent study reported on by Medical News Today suggest that the Zika virus kills brain cells and stunts growth, but it calls for further proof.