Liz Szabo

USA TODAY

Parts of the U.S. could face a year-round threat from Zika, according to a map of potential hot spots for the virus.

Researchers plotted the potential risk for Zika outbreaks in 50 large U.S. cities based on several factors, such as whether the locations are home to the Aedes aegypti mosquito that primarily spreads the virus. Researchers also considered temperature, rainfall, poverty, travel patterns and a history of other disease outbreaks caused by the mosquitoes, according to the study, led by National Center for Atmospheric Research and NASA.

Researchers estimated the overall risk of Zika, as well during each month of the year, finding that South Florida and Texas have moderate-to-high risks of the virus even in the winter, thanks to their warm temperatures, according to the study, published in PLOS Currents: Outbreaks.

It's no surprise South Florida and and the Texas-Mexico border ranked as the areas with the highest risk of Zika, said Amesh Adalja, a senior associate at the University of Pittsburgh Medical Center's Center for Health Security.

An outbreak of dengue, a viral disease also spread by Aedes aegypti, developed along the Texas-Mexico border in 2005 and in Key West in 2009 and 2010.

"We have long known where Aedes mosquitos flourish in the U.S.," Adalja said. Still, the new study could raise awareness of Zika in places that haven't paid much attention to their risk, he said. "While locales in Florida and Texas may appreciate the risk of Aedes mosquitoes, many other cities may not."

Authors of the paper estimated the risk of Zika by season, finding South Florida and Texas have moderate-to-high risks of the virus even in the winter, thanks to their warm temperatures, according to the study, published in PLOS Currents: Outbreaks.

Poverty increases the chance of Zika cases, because poor people are less likely to have window and door screens that keep mosquitoes out of the home. Impoverished neighborhoods also may have more trash on the side of the road or in yards. Trash, such as discarded tires or disposable plastic cups, can collect rain water, providing places for mosquitoes to breed.

"The best Aedes aegypti maps we have to date indicate that Zika will be mostly a Gulf Coast problem, especially in the areas of extreme poverty that are far more severe than almost anywhere else in the U.S.," said Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine in Houston.

Recent flooding in Houston and Mississippi's Gulf Coast could increase the mosquito population.

"After the floods and when the water recedes, plenty of stagnant pockets of water areas will be formed," said Mustapha Debboun, director of mosquito control at Texas' Harris County Public Health and Environmental Services. That will "create plenty of breeding habitats for mosquitoes, which will increase in larger populations as the temperature and humidity rises."

Rain water and litter are an especially bad combination when it comes to mosquitoes, Debboun said. Aedes aegypti like to breed in standing water inside man-made containers, such as discarded tires, plastic lids from disposable coffee cups and other trash.