Zika Was Spreading Long Before Experts Realized It

The Zika virus, which has caused thousands of cases of the severe birth defect microcephaly in infants, was circulating in South America for months before infections were detected, according to a new study published Wednesday in the journal Nature.

The researchers analyzed Zika virus genomes collected in 11 countries and territories from people with infections as well as mosquitoes. The analysis of over 100 Zika genomes revealed how the virus spread through central and south America and even into the United States. The researchers, including geneticist Pardis Sabeti of the Broad Institute and Harvard University and a TIME 100 honoree, report that it’s likely the Zika virus was spreading in Brazil in February 2014, which is a full year before infections of the virus were being reported.

In other countries like Columbia and Puerto Rico, the virus also appeared to be spreading many months before the countries identified the presence of infections.

“Because the data we generated capture the geographic diversity of the virus across the Americas, they provide an opportunity to trace how and when the virus spread,” said study co-author Hayden Metsky, a graduate student in the Sabeti lab, in a statement. “Our data and findings will also support development of more effective molecular diagnostic tests, as well as improved public health surveillance tools.”

In another study published in Nature, researchers looked at how the Zika virus entered the state of Florida and reported that the virus appeared to be circulating circulating in Spring of 2016, and that there was likely four different introductions of the virus into Florida that contributed to its spread.

The researchers say their study underlines the need for more sensitive diagnostic tools for infectious diseases as well as the importance of sharing information about disease spread across countries.