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Zika virus present in amniotic fluid
Researchers have detected the presence of Zika virus in the amniotic fluid of two pregnant Brazilian women whose fetuses were diagnosed with microcephaly, providing further evidence that the virus is capable of crossing the placental barrier.
While this finding details the potential transmission route of Zika virus from the mother to her fetus, more data are necessary to definitively link the infection to microcephaly, the researchers wrote in The Lancet Infectious Diseases.
“Previous studies have identified Zika virus in the saliva, breast milk and urine of mothers and their newborn babies after having given birth,” Ana M.B. de Filippis, PhD, of the Oswaldo Cruz Institute, Rio de Janeiro, said 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.”
In the case study, de Filippis and colleagues examined samples from two pregnant Brazilian women, aged 27 and 35 years. The women’s fetuses were diagnosed with microcephaly at 28 weeks’ gestation using ultrasound-guided transabdominal amniocentesis. Both women presented to care with symptoms of Zika virus infection, including fever, myalgia and rash, and they received testing for several relevant infections, including Zika virus.
Figure 1. Sequencing of Zika virus detected in the amniotic fluid of two Brazilian women revealed genetic relationships with a lineage isolated during a French Polynesian outbreak in 2013.
Source: Oswaldo Cruz Institute
Quantitative reverse transcription PCR and next-generation sequencing identified Zika virus in the patients’ amniotic fluid, but did not detect any virus in urine or serum. Sequencing and phylogenetic reconstruction of one patient’s sample found the virus to be 97% to 100% genetically similar with lineages studied during a 2013 Zika virus outbreak in French Polynesia, and no evidence for recombination events in the Zika virus genome was found.
These findings suggest a possible origin for the Zika virus currently circulating in Brazil, the researchers wrote. While the detection of virus in amniotic fluid provides some evidence toward a causal relationship between Zika virus and microcephaly, more data are needed.
“This study cannot determine whether the Zika virus identified in these two cases was the cause of microcephaly in the babies,” de Filippis said in the release. “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 a related editorial, Didier Musso, MD, professor in the emerging infectious diseases unit at the Institut Louis Malardé, Tahiti, French Polynesia, and David Baud, MD, PhD, materno-fetal medicine and obstetrics specialist at Lausanne University Hospital, Switzerland, agreed that more data are required to link the two conditions, and highlighted many of the current gaps in knowledge involving Zika virus and infant outcomes.
“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,” they wrote. “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.
“Expected complications might be similar to those of other infections assessed by the TORCH screen and include mental retardation, cerebral palsy, seizure and sensorineural hearing and visual loss. Such information is needed to allow adequate counseling in pregnant women possibly infected with Zika virus.” – by Dave Muoio
Disclosure: The researchers report no relevant financial disclosures.