Per-capita income and other economic conditions the single greatest predictor of occurrence.

Low-income neighborhoods appear to be the most susceptible to West Nile virus, a mosquito-transmitted disease that is linked to more than 1,000 deaths since in the United States since 1999, according to new UCLA-led research.

Using data on infected humans and mosquitoes from the West Nile virus hotspot of Orange County from 2005-08, scientists found that per-capita income and other economic conditions were the single greatest predictor of occurrence, explaining 85-95 percent of the variation. While economic conditions have previously been linked to disease, the study is the first to use a rigorous statistical model.

“We are seeing more West Nile virus not only in humans in these lower-income areas but in the mosquito populations as well, so the finding can’t just be attributable to differences in human behavior,” said Ryan Harrigan, a postdoctoral scholar with the Center for Tropical Research at the UCLA Institute of the Environment and Sustainability, and the study’s lead author. “Clearly, there are other factors.”

Among the potential factors influencing the prevalence of the virus in lower-income areas, researchers said, are abandoned swimming pools in areas with foreclosed homes and antiquated water runoff systems that provide favorable breeding habitat for mosquitoes. Another factor may be lower levels of political participation among residents, they said.

The research, funded by the U.S. Environmental Protection Agency, was published in the peer-reviewed scientific journal PLoS One. It was overseen by Professor Thomas Smith of the UCLA Department of Ecology and Evolutionary Biology and director of the Center for Tropical Research.

West Nile virus was first detected in North America in 1999. Mosquitoes catch it by biting infected birds, then spread it to humans. It has been linked to more than a thousand human deaths as well as significant declines in bird populations, according to the Centers for Disease Control and Prevention.

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