Satellites to Predict Disease Outbreaks

Oct. 8, 2008 -- By looking at satellite imagery, University of Maryland scientists hope to predict cholera epidemics four to six weeks before they actually happen.

The research could help save lives worldwide, and could be used to develop other models to predict other seasonal or climate-driven infectious diseases.

"Predicting the conditions that trigger cholera outbreaks in coastal regions could be very valuable for public health," said Rita Colwell, a University of Maryland scientist who has studied cholera for decades. "If we see this coming we could go into these areas with bottled water and medication to save lives."

Cholera, a disease that gives victims diarrhea so severe they can die 18 hours after their first liquid stool, is caused by a bacterium, Vibrio cholerae. Humans become infected after eating contaminated food or water. Cholera outbreaks usually occur in developing countries, such as India, Bangladesh and in Afica, although Colwell says that she's found the bacterium in Eastern U.S. coastal waters as well.

Vibrio cholerae is associated with a type of crustacean called a copepod that appears naturally in many areas of the world. The copepods feed on zooplankton, which in turn feed on phytoplankton. Phytoplankton use photosynthesis to harvest energy from the sun to create their food.

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Colwell and her colleagues use this food ladder to their advantage. Higher sea temperatures encourages photosynthesis. Higher sea levels brings that phytoplankton, and later cholera, closer to humans.

Satellites can currently measure sea temperature, sea height and chlorophyll concentrations. Colwell hopes that future satellite data will also include information on salinity, oxygen saturation and other variables, which could help increase the accuracy of their models.

Colwell and her colleagues correlated the environmental data with infection statistics in several countries to create a model that can predict the severity of cholera outbreaks four to six weeks before the first individual is infected.

At one point during their analysis the scientists had environmental data from a province in Bangladesh, a country with seasonal cholera outbreaks, but didn't know how many people had been infected with cholera.