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Chasing fire: Fever and human mobility in an epidemic

Dengue fever is common in Iquitos, Peru, a densely packed city surrounded by the Amazon. With the imminent arrival of Zika virus to Iquitos, the researchers expect that the data they have collected on dengue transmission will also add to the understanding of how Zika spreads through a population.

Disease ecologists working in the Amazonian city of Iquitos, Peru, have quantified for the first time how a fever affects human mobility during the outbreak of a mosquito-borne illness. The findings were published by Proceedings of the Royal Society B.

“When you are sick with dengue, or another illness causing fever, your behavior can change,” says Gonzalo Vazquez-Prokopec, an assistant professor in Emory University’s Department of Environmental Sciences, and senior author of the study. “We’ve found that people with a fever visit 30 percent fewer locations on average than those who do not have a fever, and that they spend more time closer to home. It may sound like stating the obvious, but such data have practical applications to understand how human behavior shapes epidemics. No one had previously quantified how a symptom such as fever changes mobility patterns, individually and across a population, in a tropical urban setting like Iquitos.”

An issue in tracking an infectious disease like dengue, chikungunya and Zika is that most of the people infected are asymptomatic, or do not have symptoms severe enough to trigger a doctor visit. “They may not feel sick at all, and yet they could be infecting others, which could help explain how these pathogens move explosively across a population,” Vazquez-Prokopec says. “We need to rethink the way we do disease surveillance and control if asymptomatic people are important drivers of transmission.”

Trying to control the spread of a disease is like chasing a fire, he adds. “You know that a fire may be at the home of a sick person but, using the data we have for current models, you don’t really know where the fire is going next.”

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