FRIDAY, May 27, 2016 (HealthDay News) -- New research seems to shed light on how the Zika virus infects, but doesn't kill, placenta cells.
The mosquito-borne virus can cause severe birth defects in babies whose mothers are exposed to Zika during pregnancy, but scientists don't know exactly how that happens.
"Our results substantiate the limited evidence from pathology case reports," said senior author Mehul Suthar, an assistant professor of pediatrics at Emory University School of Medicine, in Atlanta.
"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," Suthar said in a university news release.
Scientists conducted experiments using immune cells from placentas of healthy women who had full-term babies delivered by cesarean section.
The Zika virus used in the study is the strain circulating in Puerto Rico. The researchers said it's closely related to the strain in Brazil, where the virus-related birth defects became apparent last spring.
The researchers found that Zika can replicate in immune cells from the placenta without killing them. They said this may explain how the virus can pass through the placenta of a pregnant woman and infect developing brain cells in her fetus.
In Brazil, the result has been an estimated 5,000 cases of microcephaly, a condition in which an infant is born with an abnormally small head and underdeveloped brain.
When they examined placenta cells from different women, the researchers also found wide variation in the levels of Zika virus replication. This suggests some women may be more susceptible to infection than others, the researchers said.
"Not every pregnant woman who is infected by Zika transmits the virus to her fetus," Suthar said. "Host genetics and nonviral factors, including nutrition and microbiota, as well as timing may be influencing infectivity."
Suthar added that a better understanding of these factors could lead to preventive measures, and eventually antiviral therapies.
The study was published May 27 in the journal Cell Host & Microbe.
Zika-related viruses in the flavivirus family include dengue, West Nile and yellow fever, and are rarely transmitted from mother to fetus, the researchers noted.
"Zika may be unique in its ability to infect placental cells and cross the placental barrier, in comparison with other flaviviruses," Suthar said.
The U.S. Centers for Disease Control and Prevention has more on the Zika virus.