New Delhi

US researchers have uncovered how the Zika virus stealthily spreads within placental cells, disrupting the immune system and ultimately leading to foetal death.

Zika, transmitted by mosquitoes, is known to cause neurological disorders, foetal abnormalities and foetal death during pregnancy. However, until now, the mechanism by which the virus crosses the placenta — an essential barrier protecting the foetus — has remained unclear.

Researchers at Baylor College of Medicine and Pennsylvania State University discovered that Zika virus creates underground tunnels, called tunnelling nanotubes, which allow viral particles to transfer to neighbouring uninfected cells.

The study revealed that a Zika protein known as NS1 triggers the formation of these tunnels. "Exposure of placental cells to the NS1 protein of Zika virus triggers tunnel formation. As the tunnels develop and connect neighbouring cells, a path opens for the virus to invade new cells," explained Dr. Rafael T. Michita, postdoctoral research associate at Baylor.

Interestingly, Zika is the only virus in its family — along with dengue and West Nile viruses — whose NS1 protein triggers tunnel formation in multiple cell types. Other viruses, such as HIV, herpes, influenza A, and SARS-CoV-2, can also create tunnels in infected cells, but this is the first time tunnelling has been observed in placental cells infected by Zika.

The study, published in Nature Communications, shows that these tiny conduits not only transport viral particles but also RNA, proteins, and mitochondria—vital energy sources for cells—from infected to neighbouring cells. This transport of mitochondria could potentially provide an energy boost to infected cells, helping the virus evade antiviral defences within the placenta.

These findings provide crucial insights that could inform future therapeutic strategies to counteract this covert transmission method.