New Evidence Suggests Zika Virus Can Cross Placental Barrier

Link to microcephaly still debated

Researchers in Rio de Janeiro, Brazil, have detected Zika virus in the amniotic fluid of two pregnant women whose fetuses have been diagnosed with microcephaly, according to a study published online in Lancet Infectious Diseases. Although the report suggests that Zika can cross the placental barrier, the finding does not prove that the virus causes microcephaly; more research is needed to understand that link, the authors say.

The researchers also analyzed the genome of the virus found in the two pregnant women and confirmed that it is genetically related to a strain identified during an outbreak of Zika virus in French Polynesia in 2013.

“Previous studies have identified Zika virus in the saliva, breast milk, and urine of mothers and their newborn babies, after having given birth. This study reports details of the Zika virus being identified directly in the amniotic fluid of a woman during her pregnancy, suggesting that the virus could cross the placental barrier and potentially infect the fetus,” said lead author Dr. Ana de Filippis.

She added: “This study cannot determine whether the Zika virus identified in these two cases was the cause of microcephaly in the babies. Until we understand the biological mechanism linking Zika virus to microcephaly, we cannot be certain that one causes the other, and further research is urgently needed.”

In the new study, the researchers investigated the case of two women (27 and 35 years of age) from Paraiba, a state in northeast Brazil. The two women presented with symptoms of Zika virus infection, including fever, muscle pain, and rash, during their first trimester of pregnancy. Ultrasounds taken at approximately 22 weeks of pregnancy confirmed that the fetuses had microcephaly.

Samples of amniotic fluid were taken at 28 weeks of pregnancy and were analyzed for potential infections. Both patients tested negative for dengue virus, chikugunya virus, and other infections, including human immunodeficiency virus (HIV), syphilis, and herpes. Although the two women’s blood and urine samples tested negative for Zika virus, their amniotic fluid tested positive for the virus genome and for Zika antibodies. The RNA of the two Zika virus samples was then compared with samples from previous outbreaks and was found to be genetically related to the strain identified in French Polynesia.

In a separate commentary, Professor Didier Musso of the Louis Malarde Institute in Tahiti, French Polynesia, said: “Even if all these data strongly suggest that Zika virus can cause microcephaly, the number of microcephaly cases related to Zika virus is still unknown. The next step will be to do case-control studies to estimate the potential risk of microcephaly after Zika virus infection during pregnancy, other fetal or neonatal complications, and long-term outcomes for infected symptomatic and asymptomatic neonates.”

Sources: MedicalXpress; February 18, 2016; and Lancet Infectious Diseases; February 17, 2016.