A case study conducted in Brazil revealed the presence of Zika virus in the amniotic fluid of two pregnant women, suggesting that the virus can cross the placental barrier and potentially infect the developing fetus.
Both women in the study had their amniotic fluid samples taken at 28 weeks, and later gave birth to babies with microcephaly.
The finding, published online Feb 17 in The Lancet Infectious Diseases (Lancet Infect Dis. 2016 Feb 17. doi: 10.1016/S1473-309900095-5), does not prove that Zika virus infection causes microcephaly but does suggest the biological plausibility of such a link.
In the same study, the researchers, led by Dr. Ana de Filippis of Oswaldo Cruz Institute in Rio de Janeiro, applied reverse transcription polymerase chain reaction and viral metagenomic sequencing to the viral samples, allowing them to establish that the virus was very closely related to the Zika virus that caused an outbreak in French Polynesia in 2013, and was not a recombinant strain.
The women in the study, age 27 and 35, were from the Brazilian state of Paraíba. Neither woman reported smoking, using recreational drugs or alcohol, or taking medications known to affect fetal development.
Zika virus was not found in the blood or urine of either woman when the amniotic samples were taken, though both had reported earlier symptoms consistent with Zika infection. Other infections, including HIV, dengue, chikungunya, rubella, and herpes viruses, were ruled out.
The results provide important insight into the origin of the Zika virus circulating in Brazil, the researchers wrote in their analysis. Moreover, “our group is the first, to our knowledge, to isolate the whole genome of Zika virus directly from the amniotic fluid of a pregnant woman before delivery, supporting the hypothesis that Zika virus infection could occur through transplacental transmission,” wrote Dr. de Filippis and her colleagues.
Still, little is known about the effects of Zika on the developing central nervous system, the researchers wrote. A connection between Zika virus infections and poor CNS outcomes “remains presumptive, and is based on a temporal association. New studies should be done to investigate whether the Zika virus can infect either neurological precursor cells or final differentiated cells.”
The researchers cautioned that congenital microcephaly has been associated with genetic disorders, chemical exposures, brain injury and uterine infections. Other possible contributors to the current high rate of microcephaly in Brazil, which last year was 20 times higher than in previous years, need to be investigated, they wrote.
Agencies within Brazil’s national government and the city of Rio de Janeiro funded the study, and investigators disclosed no conflicts of interest.