Available Evidence of Association between Zika Virus and Microcephaly

To clarify the possible association between the Zika virus (ZIKV) and microcephaly and understand where we are in terms of research and the debate on the causation between mild maternal clinical features and severe fetal microcephaly.

We did a comprehensive literature review with the keywords "zika" and/or "microcephaly" from inception to May 27, 2016, with PubMed.

Studies were included and analyzed if they met all of the following criteria: "probable or confirmed infant microcephaly" and "probable or confirmed ZIKV infection among mothers or infants".

We emphasize the diagnosis of ZIKV infection, including maternal clinical manifestations, maternal and fetal laboratory confirmation, and possible autopsy if need. Other confounders that may lead to microcephaly should be excluded from the study. We presented the results from clinical manifestations of ZIKV infection, testing methods evolving but the mechanism of microcephaly uncertain, flexible definition challenging the diagnosis of microcephaly, and limited causal reference on pregnant women. We made analog comparison of severe acute respiratory syndrome and chikungunya virus in terms of DNA mutation and global movement to provide further research recommendation. The chance of catch-up growth may decrease the number of pervious "diagnosed" microcephaly.

There are some evidence available through mice models and direct isolation of ZIKV in affected pregnancies on kindly causal relationship but not convincible enough. We analyzed and presented the weakness or limitation of published reports with the desire to shed light to further study directions.