The Lancet, Child & Adolescent Health - January 12, 2018

Elizabeth B Brickley, Laura C Rodrigues

2 years after a "cluster of microcephaly cases" was detected in Brazil, scientists are still answering basic epidemiological questions. The immediate concern at the time of the epidemic was identifying the underlying cause of the neurological abnormalities. Before 2015, microcephaly was a rare but well known condition.  However, the upsurge in diagnoses in the Americas was different to previous years, and a range of potential causes were proposed. Under consideration was congenital Zika virus infection, but also alternative risk factors, including exposure to pesticides, receipt of vaccines during pregnancy, and a so-called epidemic of overdiagnosis for microcephaly. Evidence from in-vitro, animal model, and epidemiological investigations has now established a clear, causal link between Zika virus infection in pregnancy and microcephaly, and the motivating questions have shifted in focus from aetiology to that of disease burden and biological mechanisms.

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