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BOULDER, CO – How likely you are to see a Zika virus outbreak this summer varies greatly based on where you practice.
A new study led by mosquito and disease experts at the National Center for Atmospheric Research (NCAR) reports that populations of the Aedes aegypti mosquito, responsible for the spread of the virus in much of Latin America and the Caribbean, are likely to increase across much of the southern and eastern United States as the weather warms up.
The research, published recently in PLOS Currents Outbreaks, notes that 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. Those predictions are based on specialized computer simulations conceived and run by researchers at NCAR and the NASA Marshall Space Flight Center.
The mosquitoes should subside during spring and fall except for low-to-moderate populations in more southern regions, but winter is too cold for the species outside of the more southern areas of Florida and Texas, according to the simulations.
Most vulnerable overall are cities in southern Florida and areas of southern Texas, much of it poor and rural, according to researchers who determined that by analyzing travel patterns from countries and territories with Zika outbreaks.
"This research can help us anticipate the timing and location of possible Zika virus outbreaks in certain U.S. cities," said lead author Andrew Monaghan, PhD, of NCAR. "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."
Miami, Houston, and Orlando were among the cities with the highest potential numbers of Aedes aegypti as well as a large volume of air travelers. And, because nearly five times as many people cross the U.S.-Mexico border per month than arrive by air in all 50 cities, study authors wrote, that creates a high potential for transmission in border areas from Texas to California, although the Zika virus has not been widely reported in northern Mexico.
"Even if the virus is transmitted here in the continental U.S., a quick response can reduce its impact," added co-author Mary Hayden, PhD, a medical anthropologist also at NCAR.
Long-range forecasts for this summer suggest a 40-45% chance of warmer-than-average temperatures over most of the continental United States, advised study authors who also cautioned that the report doesn’t include a specific outbreak prediction for this year.
Monaghan said warmer weather would increase 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.
Even if Zika cases become more common in the United States, the disease is unlikely to spread as widely as it has in Latin America and the Caribbean, partly because Americans spend so much time in air-conditioned and largely sealed homes and offices.
Zika, first identified in Uganda in 1947, has moved through tropical regions of the world over the past decade before being introduced into Brazil last year. It burgeoned across Latin America and the Caribbean, with more than 20 countries now facing pandemics.
Study authors point out that about 80% of infected people do not have significant symptoms, and, even when symptoms appear, they tend to be relatively mild flu- or cold-like and resolve in about a week. The concern is that the disease can lead to microcephaly, a rare birth defect characterized by an abnormally small head and brain damage, when contracted by pregnant women.
The study noted that northern cities could become more vulnerable if a related species of mosquito that is more tolerant of cold temperatures, Aedes albopictus, begins to carry the virus.