# Inapparent maternal ZIKV infection impacts fetal brain development and postnatal behavior

## TL;DR

Mild Zika virus infections in pregnant mothers can subtly affect fetal brain development and later behavior in offspring, even without obvious birth defects.

## Contribution

A mouse model reveals hidden neurological and behavioral effects of mild maternal Zika virus infection on offspring.

## Key findings

- Maternal ZIKV infection during mid-gestation leads to vertical transmission without overt developmental deficits.
- Fetal brains show altered gene activity related to synaptic function and neuronal development.
- Offspring exhibit increased synaptic density, seizure susceptibility, and sex-biased behavioral changes.

## Abstract

Zika virus (ZIKV) has emerged as a significant public health concern due to its association with severe neurological outcomes in infants, including microcephaly and congenital Zika syndrome (CZS). However, while the majority of ZIKV infections during pregnancy do not result in CZS, the potential long-term neurological effects of mild or inapparent maternal infections remain poorly understood. In this study, we adapted a model of maternal ZIKV infection in human STAT2 knock-in (hSTAT2) mice to investigate the effects of ZIKV infection during mid-gestation, aiming to mirror typical asymptomatic infections as they occur in humans. We found that maternal ZIKV infection at mid-gestation leads to vertical transmission without causing overt developmental deficits or clinical signs in dams or offspring. Despite the absence of immediate clinical signs, transcriptomic analyses revealed significant changes in the developing fetal brain, particularly in genes related to synaptic function and neuronal development. These molecular alterations were associated with increased synaptic density in the hippocampus and heightened susceptibility to chemically induced seizures in offspring, suggesting subtle yet significant long-term neurological consequences. Using motion sequencing (MoSeq), an unsupervised machine learning approach that profiles naturalistic motor behavior, we also identified persistent, sex-biased alterations in the content and structure of spontaneous behavior in offspring exposed to maternal ZIKV infection. Our findings highlight that even mild maternal ZIKV infections can disrupt fetal neurodevelopment, underscoring the need for enhanced monitoring and public health measures for children exposed to ZIKV in utero but who do not experience severe developmental alterations at birth. Additionally, our study provides a valuable animal model and comprehensive, cell type-specific transcriptomic datasets that will facilitate new lines of investigation into the impact of inapparent maternal ZIKV infections on fetal and childhood brain development.

Zika virus infection during pregnancy is best known for causing severe brain and developmental abnormalities in a subset of infants. However, most exposed children are born without obvious problems, and the long-term consequences of these more common cases remain unclear. Here we used a mouse model that mimics mild, asymptomatic infection in the mother to ask whether such exposures can still alter brain development in offspring. We found that maternal infection allowed virus to reach the fetal brain without causing reduced brain size. Nevertheless, fetal brains showed broad changes in patterns of gene activity that guide how nerve cells grow and connect. As the offspring matured, they developed more excitatory synapses, became more susceptible to chemically induced seizures, and showed lasting, sex-specific changes in spontaneous behavior. Our findings suggest that even mild maternal Zika virus infections may carry hidden risks for later neurological or behavioral difficulties. These findings support the need for long-term monitoring of exposed children.