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Tracking Plagues from Space

Researchers are using satellite images to study the burrow systems of great gerbils in Kazakhstan. The density of the burrow systems is an important indicator of an impending plague. Photograph by Herwig Leirs.

Keeping deadly plagues at bay takes time, money and people to monitor the activity and concentration of host species, as is the case for the great gerbil that populates vast, isolated stretches of the former Soviet Republic of Kazakhstan.

Authorities have tracked the species for decades, and when conditions warrant, they fumigate the intricate network of burrows where the gerbils live, killing the bacteria–carrying fleas that live in the burrow systems and transmit the disease, while sparing the small mammalian hosts. Without such measures, the plague would very likely infect livestock and humans as it has done in the past (before monitoring and control systems were in place).

But as funding is cut, the number of surveillance programs is in decline, Stephen Davis, a postdoctoral scientist at the University of Utrecht in the Netherlands, explained during a recent seminar at the Yale School of Public Health. Davis plans to join Yale as a research associate in the fall.

He described efforts now underway in central Asia to where remote imaging technology is being used to scan swaths of often remote and inhospitable land for the gerbil’s burrows, the density of which can be a key indicator of an impending plague. From space, the burrow entrances appear as discs of bare soil, offset by areas of green vegetation or black lichen communities.

“So far the results are really promising,” Davis said. In addition to being able to detect the expansion or contraction of great gerbil metapopulations at the borders of their range, the satellite technique also could allow researchers to estimate the rate of expansion or contraction, clarify the epizootological regions (and identify possible connections between these regions) and estimate the abundance of great gerbils.

While the satellites have achieved 94 percent accuracy in burrow identification and can survey larger tracts of land much quicker than people on foot, it is still unknown how accurately they can differentiate between burrows in use from those that are dormant. The researchers are using pictures generated from a QuickBird satellite that collects multispectral images at 2.4–meter resolution.

“The work to distinguish dormant from active burrow systems is at a very early stage and we really have no idea if we will succeed or not. My best guess is that we will partially succeed in the sense that for some landscape types it will be possible,” Davis said.

The satellite monitoring technique could ultimately save time and money and allow researchers to pinpoint potential problems and take action before the plague poses a threat to neighboring villages or livestock.