Zika virusZika reached Miami at least four times, Caribbean travel responsible

With mosquito season looming in the Northern Hemisphere, doctors and researchers are poised to take on a new round of Zika virus infections.

Now a new study by a large group of international researchers led by scientists at The Scripps Research Institute (TSRI) explains how Zika virus entered the United States via Florida in 2016—and how it might re-enter the country this year.

Scripps says that the researchers, by sequencing the virus’s genome at different points in the outbreak, created a family tree showing where cases originated and how quickly they spread. They discovered that transmission of Zika virus began in Florida at least four—and potentially up to forty—times last year. The researchers also traced most of the Zika lineages back to strains of the virus in the Caribbean.

“Without these genomes, we wouldn’t be able to reconstruct the history of how the virus moved around,” said TSRI infectious disease researcher and senior author of the study, Kristian G. Andersen, who also serves as director of infectious disease genomics at the Scripps Translational Science Institute (STSI). “Rapid viral genome sequencing during ongoing outbreaks is a new development that has only been made possible over the last couple of years.”

The research was published in Nature. This was one of three related studies, published simultaneously in Nature journals, exploring the transmission and evolution of Zika virus. A fourth study was also published in Nature Protocols providing details of the technologies used by the researchers.

Why Miami?
By sequencing Zika virus genomes from humans and mosquitoes—and analyzing travel and mosquito abundance data—the researchers found that several factors created what TSRI Research Associate Nathan D. Grubaugh called a “perfect storm” for the spread of Zika virus in Miami.

“This study shows why Miami is special,” said Grubaugh, the lead author of the study.

First, Grubaugh explained, Miami is home to year-round populations of Aedes aegypti mosquitoes, the main species that transmits Zika virus. The area is also a significant travel hub, bringing in more international air and sea traffic than any other city in the continental United States in 2016. Finally, Miami is an especially popular destination for travelers who have visited Zika-afflicted areas.

The researchers found that travel from the Caribbean Islands may have significantly contributed to cases of Zika reaching the city. Of the 5.7 million international travelers entering Miami by flights and cruise ships between January and June of 2016, more than half arrived from the Caribbean.