Laura Gast is applying remote-sensing techniques to the test in the jungles of Peru, seeking out mosquito habitats from space in order to control the spread of dengue fever.Laura Gast uses satellites to look for mosquitoes. She can’t quite pick out individual insects from space, even though high-resolution satellite imagery has made huge strides in recent years. But she has demonstrated that she can spot the breeding grounds where they emerge, and that may be enough to one day avert an epidemic.

Gast, a doctoral student in the UAB School of Public Health whose research is funded by an Alabama Space Grant Consortium Graduate Fellowship, is focusing on the Aedes mosquito, which is responsible for spreading dengue fever and other tropical diseases. Dengue is potentially life threatening, and although it is relatively rare in the United States, up to 100 million people worldwide are infected each year. It is especially common in Peru, and Gast wanted to see if she could apply remote-sensing techniques to benefit the public’s health in that country.

Blood Enemy

Working in the UAB Laboratory for Global Observation, Gast experimented with several techniques before finding a method that would allow her to identify prime conditions for a spike in Aedes populations—including temperature and other factors—that could point to an upcoming outbreak of dengue fever. This spring, she traveled to Peru to verify her methods on-site, a vital part of the process known as “ground truthing.”

“The Aedes mosquito is what’s known as an artificial container mosquito,” Gast says. “It can’t breed in a muddy puddle on the side of the road. It prefers things like dog bowls, 55-gallon drums, and flower pots. And it can only fly 50-100 meters, so if you remove the sources of water, you can reduce the chances of the mosquito biting someone.”

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The above images are NASA Landsat near-true-color composite images of the southern Amazon basin city of Puerto Maldonado Peru from 1986 (left) and 2005 (right). Instead of the visible light from the red, green, and blue wavelengths, this image contains light from the mid-infrared and green wavelengths. Deeper green colors indicate forested areas; lighter/brighter greens indicate shrub and grass lands; browns indicate exposed dirt and barren land; white colors indicate urban or built-up land. Notice the expansion of slash-and-burned grazing land on the sides of major roads to the west and the distinct increase in the size of the urban area. Landsat data courtesy NASA; processing by Laura Gast.

Aedes has a two- to four-week incubation period, Gast explains, so when conditions are right for its eggs to flourish, advance warning could give public-health workers time to fan out in affected areas and make a difference.

Mosquito abatement programs that include spraying chemicals “are widespread, but studies show this is not a highly effective technique” to control the insects, Gast says. “The education component is the most important, but it can be the hardest to do because of staffing issues. With warning, local governments can send out their scarce public-health workers to specific neighborhoods to teach people to dump out standing water in flower pots and other containers.”

Scientists have already proved the value of predictive modeling from remote-sensing data. Several years ago, a group of NASA scientists, working with officials from the World Health Organization and other groups, “used remote sensing to stop an epidemic of Rift Valley fever six weeks before all available models said it should have started,” Gast says.