A startling new discovery on the Zika virus is cause for major concern as authorities scramble to halt the rapid spread of the disease.

Scientists at Emory University found that sexually active women were especially likely to get infected with the Zika virus, suggesting that sexual transmission may be how this disease is spreading, a groundbreaking discovery that could both help scientists find a cure and shows a worrying reality of the virus that could make it difficult to stop, according to a University of Minnesota report.

Researchers wanted to know if there were any age-related patterns for Zika infections, and to see just how big of a role sexual transmission played. They determined that 90 percent more registered Zika cases per 100,000 population happened in women at sexually active ages — between 15 and 65 — than in men of the same age.

“One group has recently discovered viral antigen in Hofbauer cells collected from placental tissue of a fetus that unfortunately died as a result of Zika virus infection,” says senior author and Assistant Professor in Pediatrics at the Emory University School of Medicine, Mehul Suthar, in the statement. “Our study indicates that this cell type may be a target for Zika virus in the placenta and replication in these cells may allow the virus to cross the placental barrier and enter the fetal circulation,” adds co-author Rana Chakraborty, a pediatric infectious disease specialist, also at Emory.

The statement adds: “One explanation for how the virus crosses the placental barrier is by initial infection of syncytiotrophoblasts, the outermost layer of cells that surrounds and nurtures the fetus. However, earlier work (10.1016/j.chom.2016.03.008) has shown that these cells can resist the virus. The work from the Suthar Lab shows that the less-differentiated cytotrophoblasts are permissive for Zika virus infection, suggesting that if the virus is able to cross the syncytiotrophoblast layer, the virus has access to target cells where it can replicate. While Hofbauer cells were identified over a century ago, very little is known about them. Overall, the Zika epidemic has helped to reveal that the placenta is one of the most understudied human organs.”