New York, Feb 22 (IANS): Zika virus can cross the placenta -- intended to protect the developing foetus -- in the first trimester to cause a high percentage of miscarriages as well as thin brain tissue and inflammation in brain cells of the foetus, researchers have found.

Zika -- linked to serious neurological problems in infants whose mothers were exposed in early pregnancy -- was considered a public health emergency by the World Health Organization in 2016.

The study conducted in a mice model revealed that the virus creates disorganisation in the cellular layers of the placenta, that keep toxins, bacteria and viruses from crossing into the placenta.

This disorganisation could be how the virus penetrates the placenta to infect the foetus, the researchers said.

"This could be why the foetuses in the Zika-infected mice were so vulnerable to either miscarriage or brain damage," said Irina Burd, a maternal/foetal medicine physician at Johns Hopkins Bloomberg School of Public Health in the US.

For the study, published in the journal Nature Communications, the team developed a new mouse model with completely intact immune systems more similar to humans and injected Zika virus directly into the reproductive tract of the pregnant mice during what would be the equivalent of the first trimester in a human.

The results showed that the viability of foetuses was reduced and the mouse pups were likely to have thinner cortexes and have inflammatory cells in the brain, as compared to those born to mothers who had a later infection.

Conversely, when the mice were infected in the equivalent of the late second trimester instead, fewer miscarriages occurred, suggesting that there is less vulnerability to Zika later in pregnancy.

"We need to find a way to stop transmission of Zika through the placenta into the foetus, because that is where the damage is being done," added Sabra L. Klein, from the Johns Hopkins Bloomberg School of Public Health.