The Hidden History of Zika Virus Transmission

Zika virus (ZIKV) transmission in the Americas was first reported in 2015 in Brazil. Since then, the virus has spread throughout the region, including locally transmitted cases in Florida and Texas. Now, three studies using ZIKV sequencing and molecular mapping reveal when the outbreak started and how it disseminated through the Americas.

Faria and colleagues analyzed 54 ZIKV genomes, including data generated by a mobile genomics laboratory that traveled around northeast Brazil in 2016. By comparing these sequences to those from other parts of the Americas and to previously compiled sequences from Asian genotype viruses, the investigators date the common ancestor of ZIKV in the Americas to early 2014, more than a year before the first reported cases. The genetic evidence shows that the virus then spread from northeast Brazil to the Caribbean, Central America, and other parts of South America, with up to 12 months of cryptic transmission before the disease was detected.

These conclusions are supported by the findings of Metsky and colleagues, who generated 110 ZIKV genomes from clinical specimens and mosquitos in 10 North, Central, and South American countries and territories. Using phylogenetic analyses, they conclude that ZIKV had multiple introductions into the continental U.S. These results are extended by Grubaugh and colleagues, who find evidence for at least 4 — and perhaps as many as 42 — separate introductions of ZIKV in Florida, with the main source likely to be people who had been in the Caribbean.