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Potential Zika virus risk estimated for 50 US cities

Key factors that can combine to produce a Zika virus outbreak are expected to be present in a number of U.S. cities during peak summer months, new research shows.

The Aedes aegypti mosquito, which is spreading the virus in much of Latin America and the Caribbean, will likely be increasingly abundant across much of the southern and eastern United States as the weather warms, according to a new study led by mosquito and disease experts at the National Center for Atmospheric Research (NCAR).

Summertime weather conditions are favorable for populations of the mosquito along the East Coast as far north as New York City and across the southern tier of the country as far west as Phoenix and Los Angeles, according to specialized computer simulations conceived and run by researchers at NCAR and the NASA Marshall Space Flight Center.

Spring and fall conditions can support low to moderate populations of the Aedes aegypti mosquito in more southern regions of its U.S. range. Wintertime weather is too cold for the species outside southern Florida and southern Texas, the study found.

By analyzing travel patterns from countries and territories with Zika outbreaks, the research team further concluded that cities in southern Florida and impoverished areas in southern Texas may be particularly vulnerable to local virus transmission.

“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.

Although the study does not include a specific prediction for this year, the authors note that long-range forecasts for this summer point to a 40-45% chance of warmer-than-average temperatures over most of the continental United States. Monaghan said this could lead to increased suitability for Aedes aegypti in much of the South and East, although above-normal temperatures would be less favorable for the species in the hottest regions of Texas, Arizona, and California.

Monaghan stressed that, even if Zika establishes a toehold in the mainland United States, it is unlikely to spread as widely as in Latin America and the Caribbean. This is partly because a higher percentage of Americans live and work in air-conditioned and largely sealed homes and offices.

The study was published yesterday in the peer-reviewed journal PLOS Current Outbreaks. It was funded by the National Institutes of Health, NASA, and the National Science Foundation (NSF), which is NCAR’s sponsor. It was co-authored by scientists at the NASA Marshall Space Flight Center, North Carolina State University, Maricopa County Environmental Services Vector Control Division, University of Arizona, and Durham University.