London School of Hygiene & Tropical Medicine

Zika virus has been identified in the amniotic fluid of two women whose unborn children have been diagnosed with congenital microcephaly, according to a new study published in The Lancet Infectious Diseases.

In this case study, led by researchers in Brazil, amniotic fluid samples were obtained from two pregnant women whose foetuses have been diagnosed with microcephaly, and who had Zika-like symptoms while pregnant. The researchers used genomic methods to show that Zika virus was present in the amniotic fluid, indicating that the virus can cross the placental barrier. These findings may strengthen the putative link between the virus and microcephaly, the congenital birth defect in which babies are born with abnormally small heads and associated developmental delays.

The amniotic fluid was also tested for dengue virus, chikungunya virus, Toxoplasma gondii, rubella virus, cytomegalovirus, herpes simplex virus, HIV, Treponema pallidum and parvovirus B19; none of which were present.

Commenting on the findings, Jimmy Whitworth, Professor of International Public Health at the London School of Hygiene & Tropical Medicine, said:

"This study does strengthen the body of evidence that Zika virus is the cause of foetal microcephaly in Brazil. The investigators have shown that the virus crossed the placental barrier during the first and second trimesters of pregnancy in two women with fever and rash. Importantly they did not find evidence of any other of the main infections known to cause microcephaly.

"Studies of this sort can show an association between Zika and microcephaly but cannot show that Zika virus definitely caused the microcephaly. This will require the accumulation of evidence from a variety of studies from different perspectives. Questions that we urgently need to answer include what is the added risk of microcephaly if a woman has Zika virus infection in pregnancy, is the timing of infection during pregnancy important, and does Zika virus infection alone cause this birth defect or is a co-factor involved.

"Interestingly this study suggests very close resemblance of the virus recovered from these women in Brazil with viruses recovered in French Polynesia in 2013, but only about 90% resemblance with Zika viruses from Uganda. This raises questions about how effective pre-existing immunity in Africa populations would be if the outbreak in Latin America were to spread to Africa."

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