Zika reached Miami at least four times, Caribbean travel responsible
Killing Mosquitos Shows Results
The researchers believe Zika virus may have started transmission in Miami up to forty times, but most travel-related cases did not lead to any secondary infections locally. The virus was more likely to reach a dead end than keep spreading.
The researchers found that one reason for the dead-ends was a direct connection between mosquito control efforts and disease prevention. “We show that if you decrease the mosquito population in an area, the number of Zika infections goes down proportionally,” said Andersen. “This means we can significantly limit the risk of Zika virus by focusing on mosquito control. This is not too surprising, but it’s important to show that there is an almost perfect correlation between the number of mosquitos and the number of human infections.”
Based on data from the outbreak, Andersen sees potential in stopping the virus through mosquito control efforts in both Florida and other infected countries, instead of, for example, through travel restrictions. “Given how many times the introductions happened, trying to restrict traffic or movement of people obviously isn’t a solution. Focusing on disease prevention and mosquito control in endemic areas is likely to be a much more successful strategy,” he said.
When the virus did spread, the researchers found that splitting Miami into designated Zika zones—often done by neighborhood or city block—didn’t accurately represent how the virus was moving. Within each Zika zone, the researchers discovered a mixing of multiple Zika lineages, suggesting the virus wasn’t well-confined, likely moving around with infected people.
Andersen and Grubaugh hope these lessons from the 2016 epidemic will help scientists and health officials respond even faster to prevent Zika’s spread in 2017.
Behind the Data
Understanding Zika’s timeline required a large international team of scientists and partnerships with several health agencies. In fact, the study was a collaboration of more than sixty researchers from nearly twenty institutions, including study co-leaders at the U.S. Army Medical Research Institute of Infectious Diseases, Florida Gulf Coast University, the University of Oxford, the Fred Hutchinson Cancer Research Center, the Florida Department of Health and the Broad Institute of MIT and Harvard.
The scientists also designed a new method of genomic sequencing just to study the virus. Because Zika virus is hard to collect in the blood of those infected, it was a challenge for the researchers to isolate enough of its genetic material for sequencing. To solve this problem, the team, together with Joshua Quick and Nick Loman at the University of Birmingham in the United Kingdom, developed two different protocols to break apart the genetic material they could find and reassemble it in a useful way for analysis.
With these new protocols, the researchers sequenced the virus from 28 of the reported 256 Zika cases in Florida, as well as seven mosquito pools, to model what happened in the larger patient group. As they worked, the scientists released their data immediately publicly to help other scientists. They hope to release more data—and analysis—in real time as cases mount in 2017.
The new study was published with three companion papers, also in Nature journals, that explore Zika’s spread in other parts of the Americas (see sidebar).
— Read more in Nathan D. Grubaugh et al., “Genomic epidemiology reveals multiple introductions of Zika virus into the United States,” Nature (24 May 2017) (DOI: 10.1038/nature22400)
