ZIKA Virus associated with Microcephaly: the risk is quantified for the first time

In a study published on March 16, in « The Lancet », the Pasteur Institute confirmed the growing risk of microcephaly for the fetus/newborn of a mother infected with the Zika virus during the first trimester of pregnancy.

A mother infected with the Zika virus during her first trimester of pregnancy would have 50 times greater risk of having a baby with microcephaly, a serious malformation of the head. This has been demonstrated for the first time in a study conducted by the Pasteur Institute and Polynesian researchers based on data from women affected by the Zika virus in French Polynesia between September 2013 and July 2015.

Using a mathematical model, the study demonstrates that the risk of microcephaly is approximately 1% for a fetus/newborn when the mother is infected by the Zika virus during the first trimester of pregnancy, compared to a normal risk of 0.02%.

Out of the 8 microcephaly cases identified, 7 occurred in the 4-month period following the Zika virus outbreak, indicating a strong time concurrence (88%) between the epidemic and the occurrence of microcephaly.

Research on the correlation between microcephaly of the fetus and Zika virus infection has been growing these last months.

During the month of February, a team of Brazilian researchers announced having identified the Zika virus in amniotic fluid of two pregnant women (in The Lancet Infectious Diseases).

At the beginning of March, in a study published in the American journal Stem Cell, another team of researchers demonstrated by a laboratory experience that Zika virus could attack and destroy human cerebral cells.

It is in this context that for the first time, the Pasteur Institute’s study reports calculated data for the correlation between Zika virus infection and the occurrence of microcephaly.

According to the Pasteur Institute, the risk of 1% is much less than that observed during other viral infections associated with complication during pregnancy, such as rubella, which has a risk of 38 to 100%. Health authorities are preoccupied with the high proportion of individuals infected during the Zika epidemics. Since the beginning of the year, this recurrent fear of a high number of microcephaly cases has led to strong pressure by international organizations for Brazil to modify its policy on abortion access.

The conclusions of this first study, using a mathematical model, will have to be confirmed by additional research work in the coming months.

Furthermore, the results published by the Pasteur researchers were only carried out on mothers with confirmed contamination. It is still to be examined if non-symptomatic forms of Zika infection also carry a risk for the fetus.