Study Researchers: Zika Can Cross Placental Barrier

More research required to confirm link between Zika and microcephaly.

Zika virus can cross the placental barrier, although more research is required to confirm the link between the virus and microcephaly, according to a study published in The Lancet Infectious Diseases.

The virus was identified in the amniotic fluid of 2 pregnant women whose fetuses had been diagnosed with microcephaly, according to the report. Researchers analyzed the genome of the virus found in both women, and confirmed that the strain is related to those identified during a Zika virus outbreak 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,” noted lead author Ana de Filippis, PhD, of the Oswaldo Cruz Institute in Rio de Janeiro, Brazil, in a press release. “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.”

The 2 women, 27 and 35 years of age, presented with symptoms of Zika virus including fever, muscle pain, and a rash during 18 and 10 weeks of gestation, respectively.  Both women had ultrasounds taken at approximately 22 weeks, which confirmed that the fetuses had microcephaly.

At 28 weeks, samples of amniotic fluid were taken and analyzed for infection. Both women tested negative for dengue virus, chikungunya virus, Toxoplasma gondii, rubella virus, cytomegalovirus, herpes simplex virus, HIV, Treponema pallidum, and parvovirus B19.

Although blood and urine samples from both women tested negative for Zika virus, the amniotic fluid samples tested positive for Zika virus and Zika antibodies. Researchers analyzed the amniotic fluid with metagenomic analysis, which detects any microorganisms present in the samples, but only the Zika virus genome was found.

“This study cannot determine whether the Zika virus identified in these two cases was the cause of microcephaly in the babies,” Dr de Filippis explained. “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.”

Last week, a group of Argentinean physicians refuted the association between Zika and microcephaly. They claimed in their report that a larvicide called pyriproxyfen is the likely source of increased cases of microcephaly cases in Brazil. However, Brazil’s Ministry of Health responded to this claim, stating “Unlike the relationship between the Zika virus and microcephaly, which has had its confirmation attested in tests that indicated the presence of the virus in samples of blood, tissue and amniotic fluid, the association between the use of pyriproxifen and microcephaly has no scientific basis.”


1. Calvet G, Aguiar RS, Melo ASO, et al. Detection and sequencing of Zika virus from amniotic fluid of fetuses with microcephaly in Brazil: a case study. Lancet Infect Dis. 2016; doi: 10.1016/S1473-3099(16)00095-5.

2. The Lancet Infectious Diseases. New evidence suggests Zika virus can cross placental barrier, but link with microcephaly remains unclear. Accessed February 17, 2016. 

3. Brazilian Ministry of Health. Dengue, Chikungunya, e Zika. Accessed February 17, 2016.