The increase in congenital microcephaly observed in Brazil is of concern. Its emergence a few months after the introduction of Zika virus (ZIKV) infection into the country raises questions about the possible role of the infection in congenital microcephaly.
There is currently only ecological evidence of an association between the two events. A possible causative nature of the association cannot be ruled out with the evidence available. Further investigations and studies will contribute to a better characterisation of the association, and provide a better understanding of the possible role of other prenatal infections, genetic risk factors, environmental exposure to chemicals or consumption of of teratogenic drugs. Studies of the ZIKV genome will provide information on possible changes that might influence ZIKV disease characteristics and vector competence.