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University of Utah researchers have demonstrated that the risk of hantavirus outbreaks can be predicted months in advance by monitoring vegetation cover from satellites.
The deadly disease is carried by deer mouse, which inhabit the Four Corners Region and whose numbers fluctuate dramatically with precipitation amounts. In a study to be published online Wednesday, an interdisciplinary team led by biologist Denise Dearing reported that satellite imagery correlates strongly with changes in mouse populations.
The technique could be used to track outbreak risk associated with other diseases carried by animals that rely on vegetation, she said.
"It's a way to remotely track a disease without having to go out and trap animals all the time," said Dearing, a professor of biology who worked with U. geographers to produce the study.
In the Southwest, wet weather spurs growth in juniper and sagebrush, which boosts the food sources for mice by supplying them with seeds and insects. This poses a public health menace because deer mice can transmit hantavirus to humans who inhale dried mouse urine. Mortality rates are as high as 42 percent and there is no cure or vaccine.
Dearing has been studying 12 deer mouse populations in Juab County since 2002 under a National Science Foundation grant that expired in December. Her team has tracked 5,265 mice over the years and produced several studies, with more on the way. Researchers set 1,728 traps for three consecutive nights for each spring and fall field season. For every mouse captured, they recorded its gender, weight and condition and took a blood sample to determine whether it was infected.
The latest research, published in the journal Global Ecology and Biogeography, examined data collected from 2004 to 2006, when mice populations saw a three-fold increase but the prevalence of hantavirus remained constant, about 15 to 25 percent.
"The point of this whole exercise is to develop disease-risk maps, which would show the distribution of infected hosts — in this case, deer mice — overlaid with human population density," said co-author Thomas Cova, an associate professor of geography, in a press statement. "Although the focus of this work is hantavirus in deer mice, it contributes to our broader understanding of how to monitor the spread of infectious diseases from space, which in the long run could save lives."
The scientists correlated the mouse population data with satellite images colored coded to reflect relative abundance of vegetation. Changes in mouse numbers tracked closely to changes in vegetation, but the closest correlations occurred one and 1.3 years later after the landscape achieved peak greenness.
"They get fat, population density goes up, and about a year-and-a-half later population peaks," Cova said. His co-authors include geographers Lina Cao, a graduate student, and professor Philip Dennison.