The Zika epidemic began long before anyone noticed

Outbreak arrived in Brazil and invaded Florida several times without detection

Zika virus

ON THE MOVE  Researchers used genetic information from Zika virus (illustrated) to follow its spread among affected regions in South and Central America and the Caribbean.

urfinguss/iStockphoto

The Zika virus probably arrived in the Western Hemisphere from somewhere in the Pacific more than a year before it was detected, a new genetic analysis of the epidemic shows.