In:

Nature

Author:

Declan Butler

Before October 2015, the few scientists who knew much about the Zika virus could have summed it up in two words: mostly harmless.

That’s still largely true. The virus, which is mainly spread by the Aedes aegypti mosquito, causes no or very mild symptoms in most people who catch it. But last October, northeastern Brazil reported an abrupt rise in the number of babies born with an abnormally small head, a condition known as microcephaly. The timing roughly coincided with outbreaks of Zika months earlier, and since then scientists have been scrambling to find out just how harmful the virus might be to fetuses.

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