How Does Zika Virus Infect Placenta And Fetus?

A new study by scientists shows how the Zika virus infects placental immune cells without killing them. It also reveals how the virus can travel through the placenta of pregnant women and reach the brain cells in their fetuses.

"Our results substantiate the limited evidence from pathology case reports," said Mehul Suthar of the Emory University School of Medicine and senior author of the study. "It was known that the virus was getting into the placenta. But little was known about where the virus was replicating and in what cell type."

The team made use of cells from full-term placentae collected from healthy volunteers who delivered babies through the Cesarean section.

The team found that Zika virus can infect placental macrophages in cell culture, and also another type of placental cell called cytotrophoblasts, even though it took two days for it to happen. Moreover, the viral replication was found to vary according to the donor, indicating that some placentae may be more vulnerable to the virus than others.

"Not every pregnant woman who is infected by Zika transmits the virus to her fetus," Suthar said. "Host genetics and non-viral factors, including nutrition and microbiota, as well as timing may be influencing infectivity. A better understanding of these factors could allow the design of preventive measures, and eventually antiviral therapies."

Other flaviviruses that were related to Zika, such as dengue, West Nile, and yellow fever, do not transcend the placental barrier much. This marked out Zika as unique, a nodal point for the current study on this virus family.

"Zika may be unique in its ability to infect placental cells and cross the placental barrier, in comparison with other flaviviruses," Suthar said.

How and why the Zika virus impacts the fetuses of pregnant women will be studied by the Emory University team. It is continuing to investigate placental cells as well as their immunology, with the help of cells taken from humans as well as animals.

"We need to answer questions such as: what are the receptors that allow the virus to enter Hofbauer cells," Suthar said. "Do these cells change in their immune status during the different phases of pregnancy?"

The findings were published May 27 in the journal Cell Host & Microbe.