Counties in yellow recorded one year of A. aegypti being present; those shown in orange recorded two years; and those shown in red, three or more years.CDCWith the Zika virus making daily headlines, public health officials in the U.S. are bracing for the pathogen’s arrival in the lower 48 states. Earlier this spring, the US Centers for Disease Control and Prevention (CDC) released a map that painted a dire picture; summertime temperatures could support populations of Aedes aegypti—the mosquito species that carries Zika, dengue, chikungunya, and other viruses—as far north as Ohio and New Jersey and as far west as California. But researchers at CDC’s Division of Vector-Borne Diseases in Fort Collins, Colorado, published a new map in the Journal of Medical Entomology last week (June 9). And this one suggests a much more constrained range for the Zika-transmitting insects: between January 1995 and March 2016,...

“The new map is more accurate than the initial one,” Thomas Scott, an entomologist at the University of California, Davis, who wasn’t involved with the study, told NPR’s Shots. “The distribution of the A. aegypti mosquito is much more restricted than the initial map showed.”

But the new map also shows areas of the country that haven’t historically hosted A. aegypti and other tropical and subtropical disease vectors. These include central California, parts of the Bay Area, Washington, D.C., regions in the Southwest, and the Dallas-Fort Worth area. The CDC researchers compiled the map based on county records supplied by mosquito control agencies, university researchers, and state and local health departments.

Study coauthor Johan-Paul Mutebi of the CDC told NPR that the new map shows different trends than those portrayed in the earlier agency map. “The first map showed where the climate is able to sustain populations of A. aegypti,” he said. “This new map shows reports from counties where these mosquitoes were found in the last 20 years.”

And the reports used to create the map may be incomplete. “Our findings underscore the need for systematic surveillance of A. aegypti and A. albopictus in the United States and delineate areas with risk for the transmission of these introduced arboviruses,” Mutebi and his coauthors wrote in their paper.

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