Researchers in Brazil have detected traces of the Zika virus in the amniotic fluid of two fetuses with microcephaly, further bolstering the connection between the two. However, questions still remain.
The new study, published in Lancet Infectious Diseases, suggests that Zika can cross the placental barrier, but it doesn't prove that the virus causes microcephaly, a condition in which babies are born with abnormally small heads and brains. It's not the smoking gun that scientists are looking for, but it strongly suggests a link; the placental barrier regulates the exchange of substances — including infectious diseases — between mother and and foetus, while the amniotic fluid is the protective liquid around the foetus. The new study suggests that Zika is capable of breaching these built-in defence mechanisms in the mother's womb.
"This study cannot determine whether the Zika virus identified in these two cases was the cause of microcephaly in the babies," noted study author Ana de Filippis in a statement. "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."
Since the Zika virus became active in Brazil two years ago, cases of microcephaly have increased twenty-fold compared to previous years, prompting health officials to suspect a link. Prior to this latest study, CDC researchers found traces of Zika in the placentas of two women who miscarried their babies and in the brains of two newborns who died from complications arising from microcephaly, while researchers from Slovenia discovered traces of Zika in the brain tissue of a foetus whose mother became infected with the virus. Other studies have detected Zika virus in the saliva, breast milk, and urine of mothers and their newborn babies after giving birth.
The absence of a definitive cause of microcephaly has prompted a number of conspiracy theories. The latest research should quell some of these wild speculations, for which there is literally no empirical grounding.
For the new study, researchers analysed samples of amniotic fluid at 28 weeks of pregnancy in Zika-infected women who exhibited symptoms (only 20 per cent of people infected with Zika show overt signs of infection, such as fever and rash). The women's blood and urine samples tested negative for Zika, but their amniotic fluid tested positive — both for the virus genome and for Zika antibodies. The researchers also confirmed that the virus is genetically related to the strain identified during an outbreak in French Polynesia in 2013.
"[Our] results suggest that the virus can cross the placental barrier," conclude the scientists in their study. "As a result, Zika virus should be considered as a potential infectious agent for human fetuses."
But what's needed now are studies showing how the Zika virus is actually capable of affecting the neuronal cells of fetuses, along with research showing the rate of potential risk for microcephaly in the event of Zika infection during pregnancy.