Zika virus has unique ability to cross placenta and infect developing brain of fetus

A new study from Emory University has discovered that the Zika virus apparently has a unique ability to cross from mother to fetus through the placenta. Typically the placenta plays a protective role in the development of a fetus. Zika, however, passes through the placenta to cause birth defects, such as microcephaly, in the developing fetus.

Study author and pediatrics professor Dr. Mehul Suthar said, “Our results substantiate the limited evidence from pathology case reports.” He added that little is known about exactly how the Zika virus replicates in the placenta.

The study examined cells donated by healthy women who had Cesarean births at full term. The researchers found that Hofbauer cells, protective cells produced by growing fetuses, did not kill Zika cells, which instead continued reproducing, causing unusual signs of antiviral and inflammatory responses in the Hofbauer cells. This caused the researchers to question which of the receptors was allowing the virus to enter the Hofbauer cells, and whether or not their immune status was altered during the different stages of pregnancy.

Results of the study help to explain why the highest risk of Zika infection occurs during the first and early second trimesters of pregnancy. This is the time when the placenta has not developed enough to ward off infection. The researchers found that resistance to Zika varies among pregnant women, which partly explains why only some women infected with Zika have babies affected by the virus.

Suthar said, “Host genetics and non-viral factors, including nutrition and microbiota, as well as timing may be influencing infectivity.” He said that understanding these factors better could help design preventative measure.

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