With the Zika virus running rampant through South America, outbreaks could pop up in several US cities. A study from the National Center for Atmospheric Research (NCAR) estimated this hazard in the largest cities in the US, finding that the south and especially the southeast is quite vulnerable to the threat posed by Zika.

Many US cities face potential risk in summer of low, moderate, or high populations of the mosquito species that transmits Zika virus (colored circles). The mosquito has been observed in parts of the United States (shaded portion of map) and can establish populations in additional cities because of favorable summertime meteorological conditions. In addiiton, Zika risk may be elevated in cities with more air travelers arriving from Latin America and the Caribbean (larger circles). This image is freely available for media & nonprofit use.
Credit: Image based on data mapped by Olga Wilhelmi, NCAR GIS program.

Key factors can combine to produce a devastating Zika outbreak, and those unfortunate conditions may very well allign in some American cities. The Aedes aegypti mosquito, which is spreading the virus in much of Latin America and the Caribbean, will start moving more and more to the north as the weather warms up. The east coast is in a similar situation, with higher temperatures than most of the ocuntry. Summertime weather conditions are highly favorable for mosquito populations as far north as New York City and across the southern tier of the country as far west as Phoenix and Los Angeles, NCAR models showed. Wintertime conditions are too cold across all the country, bar southern Florida and Texas. However, it’s especially these (often impoverished) areas that especially vulnerable in the case of an outbreak.

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“This research can help us anticipate the timing and location of possible Zika virus outbreaks in certain U.S. cities,” said NCAR scientist Andrew Monaghan, the lead author of the study.

“While there is much we still don’t know about the dynamics of Zika virus transmission, understanding where the Aedes aegypti mosquito can survive in the U.S. and how its abundance fluctuates seasonally may help guide mosquito control efforts and public health preparedness.”

“Even if the virus is transmitted here in the continental U.S., a quick response can reduce its impact,” added NCAR scientist Mary Hayden, a medical anthropologist and co-author of the study.

The study doesn’t propose a fixed chance for this year, but even in the case of an outbreak, it wouldn’t be as dramatic as it was in South America. A higher percentage
of Americans live in air-conditioned conditions or in sealed offices, and green areas and parks are often sprayed with insecticide. But this doesn’t mean that there is
no risk.

Aside for meteorological conditions, poverty and lack of access to proper sanitation also favorize the spread of the virus. Add to this the higher mobility of people
from the US, and you could end up with a recipe for disaster. All in all, this is a complex issue, and a disease we don’t properly understand yet. If we want to avoid
a global outbreak, basic precautions have to be set.

“The results of this study are a step toward providing information to the broader scientific and public health communities on the highest risk areas for Zika emergence in the United States,” said Kacey Ernst, an epidemiologist at the University of Arizona and co-author of the study. “We hope that others will build on this work as more information becomes available. All areas with an environment suitable to the establishment of Aedes aegypti should be working to enhance surveillance strategies to monitor the Aedes aegypti populations and human populations for disease emergence.”

“This research highlights the complex set of human and environmental factors that determine whether a mosquito-borne disease is carried from one area to another, and how severely it affects different human populations,” said Sarah Ruth, program director in NSF’s Division of Atmospheric and Geospace Sciences. “By integrating information on weather, travel patterns, mosquito biology, and human behavior, the project team has improved our ability to forecast, deal with, and possibly even prevent future outbreaks of Zika and other serious diseases.”

Journal Reference:

Andrew Monaghan, Cory Morin, Daniel Steinhoff, Olga Wilhelmi, Mary Hayden, Dale Quattrochi, Michael Reiskind, Alun Lloyd, Kirk Smith, Christopher Schmidt, Paige Scalf and Kacey Ernst. On the seasonal occurrence and abundance of the Zika virus vector mosquito Aedes aegypti in the contiguous United States. PLOS Currents Outbreaks,
2016