Spotting disease from space

THE IMMEDIATE effects of the earthquake that hit El Salvador were devastating. But over the next few weeks, disease may take an even heavier toll. Combining satellite data with ecological and social maps could help dampen these `disease aftershocks'.

Many diseases ride on the coat-tails of natural disasters. Damaged water and food supplies can bring typhoid and cholera. Standing water can spread mosquito-borne diseases such as malaria. People forced to sleep outside are more vulnerable to mosquito bites. And infections such as measles and meningitis sweep through overcrowded refugee camps.

Stephen Guptill, of the U.S. Geological Survey (USGS), described how satellites may be the best way to gauge the extent of a disaster and find the people displaced by it, particularly in remote and undeveloped areas. This information can then be fed into a geographic information system - basically a detailed, computerized map - and combined with, for example, census data or information on the distribution of mosquitoes, to deduce the risk of certain diseases.

The USGS and the U.S. Centers for Disease Control and Prevention (CDC) are currently developing these ideas in the southeastern United States. This area is prone to hurricanes and tropical storms, and home to severe mosquito-borne diseases such as encephalitis. Were a flood to strike here in the future, the plan is to add what is known about the distribution and habitat preferences of the mosquito that spreads encephalitis to satellite images of flooded areas to pinpoint where the CDC's teams should hunt for disease-carrying insects.

This information could then be combined with census data - even to the extent of matching the age of populations to disease risk - to design the best response in terms of, say, pesticide spraying or evacuation. Chester Moore, a CDC researcher working on this project, says that such a system would certainly improve on the CDC's previous approach, which involved "flying in, renting a car, buying a map from a gas station and driving around looking for sites".

Cheap global positioning systems and palmtop computers are making this data easier to collect, and the Internet is making it easier to distribute it to the people on the ground who could put it to use. In the future the World Health Organization or the International Red Cross could use this information on a global scale to coordinate response to disasters and identify risks in advance of any disaster, Guptill envisages.

Having this information is one thing, putting it to use in a chaotic disaster zone is quite another. And census and ecological information in developing countries is often very poor.

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