The new research suggests that Zika could also get to the fetus via another route, beginning in the second trimester, crossing the membrane that forms the amniotic sac in which the fetus develops. Cells in that membrane were able to be infected with Zika too, the researchers found.

“The fact that the cells in the amniochorionic membranes, they were pounding out all this virus, we thought, wow, maybe that’s actually a second route,” said Eva Harris, an expert on infectious diseases and vaccines at University of California, Berkeley.

The researchers reported that the Zika virus binds consistently to a protein in different placental cells called TIM1. They also found that a drug, an antibiotic called Duramycin that is currently approved to treat animals but not people, appears to block Zika from attaching to the protein.

That does not mean that Duramycin could be used to treat Zika infection in pregnant women, experts cautioned. Wei Zheng, who runs a lab in the federal Therapeutics for Rare and Neglected Diseases program and is testing drugs as potential Zika treatments, said that Duramycin’s molecules were too large to reach the brain and possibly the fetus. He added that the drug, which is in early clinical trials for cystic fibrosis patients, would need considerably more testing to determine its safety for pregnant women.