Zika virus can cross the placental barrier, according to new study

By Sally Robertson, B.Sc.Feb 18 2016

A study of pregnant women in Brazil has confirmed the presence of Zika virus in the amniotic fluid of two women who had displayed Zika-like symptoms during their pregnancies. The women’s fetuses had also been diagnosed with microcephaly, a birth defect where babies are born with abnormally small heads and an increased likelihood of incomplete brain development.

Brazil has seen a 20-fold increase in the number of babies born with microcephaly over the last year, when the country also saw a rise in the number of Zika virus infections, which has led researchers to speculate that the two are linked.

Scientists say that although the current study does not prove that Zika virus causes microcephaly, it does suggest that the virus can cross the placental barrier and has strengthened the theory that the virus is linked to this birth defect.

As reported in The Lancet Infectious Diseases, Ana de Filippis (Oswaldo Cruz Institute in Rio de Janeiro, Brazil) and team studied two women (aged 27 and 35) who had displayed symptoms of Zika infection including rashes, fever and muscle pain during the first trimester of pregnancy. Ultrascans at 22 weeks of pregnancy also showed that their fetuses had microcephaly.

At 28 weeks of pregnancy, the researchers performed metagenomic analysis of amniotic fluid samples taken from the women. Both patients tested positive for Zika virus and were negative for other viruses or bacteria that can cross the placental barrier such as HIV, chikungunya, herpes syphilis and dengue fever. The analysis also showed that the virus was genetically related to the strain identified during a Zika virus outbreak in French Polynesia in 2013.

Professor Jimmy Whitworth from the London School of Hygiene and Tropical Medicine says that while the research cannot prove the link between microcephaly and Zika, it “does strengthen the body of evidence that Zika virus is the cause of fetal microcephaly in Brazil."

Further research is urgently needed because:

Until we understand the biological mechanism linking Zika virus to microcephaly we cannot be certain that one causes the other.”

Dr Ana de Filippis (Oswaldo Cruz Institute in Rio de Janeiro, Brazil).

Brazil has about 508 confirmed cases of microcephaly and 3,935 suspected cases are currently being investigated. Experts advise that pregnant women are most at risk from Zika virus and should try to protect themselves from being bitten by mosquitoes.