Volume 8, Number 4     July/August 2000

Satellites Helping to Predict Outbreaks

NASA is providing new insights from space that may help health officials predict outbreaks of deadly water-borne cholera, a bacterial infection of the small intestine that can be fatal to humans.

Scientists have learned how to use satellites to track blooms of tiny floating plant and animal plankton that carry cholera bacteria by using satellite data on ocean temperatures and other climate variables. The work is described in a recent paper, co-authored by the University of Maryland Biotechnology Institute (UMBI) and NASA researchers, that appeared in the Proceedings of the National Academy of Sciences.

“These experiments fulfill our hypothesis that cholera is associated with environmental conditions,” said Dr. Rita Colwell, co-author of the cholera-tracking project paper. She is founder and former president of UMBI, and is now director of the National Science Foundation. She is presently on leave of absence from the University of Maryland.

The authors found that rising sea temperatures and ocean height near the coast of Bangladesh in the Bay of Bengal from 1992 to 1995 often preceded sudden growth, or “blooms,” of plankton and outbreaks of cholera. Similar application of risk analysis developed by NASA using satellite data has also been used in the study of diseases such as malaria, Lyme disease and Rift Valley fever.

“When such a model for Bangladesh is extended to the global scale, it may serve as an early warning system, enabling effective deployment of resources to minimize or prevent cholera epidemics in cholera-endemic regions,” said Brad Lobitz, principal author of the paper and a scientist at NASA’s Ames Research Center in Moffett Field, California. The scientists correlated years of hospital cholera records from Bangladesh with sea temperature and ocean height data that came from a variety of satellites and surface observations.

Satellites can measure water temperature and ocean height, and can measure colors that indicate plankton and chlorophyll over a large sea area, Lobitz explained. Tracking sea temperatures from ships and by other direct measurements is too expensive to be practical, he added.

Cholera may result in extreme diarrhea, vomiting and loss of water. Victims can die within a day or so unless body fluids are replenished quickly. The seventh cholera pandemic began in 1961 and now affects six continents, according to the paper. A pandemic is an epidemic that occurs over a large region.

Sea height is important because tides reach further inland to affect more people who may drink or bathe in brackish water carrying cholera. “Bangladesh is very low and flat, and tidal effects are felt almost halfway up into the country,” said co-author Louisa Beck of California State University at Monterey Bay and a resident scientist at Ames.

“The 1992—1995 study is important because all the remote sensing satellite data are in the public domain,” Beck said “…we obtained the data at no cost because it is available on the web.”

“In most years Bangladesh has two cholera outbreaks,” Lobitz said. “These are in the spring and fall.” The authors discovered that the sea surface temperatures show an annual cycle similar to the cholera-case data.

The effort was a cooperative project between NASA’s Office of Life and Microgravity Sciences and Applications and UMBI. The study was also supported by grants from the National Institutes of Health and the Environmental Protection Agency. Other authors include Byron Wood, Ames; Anwar Huq, UMBI; and George Fuchs and A.S.G. Faruque, the International Centre for Diarrhoeal Disease Research, Bangladesh.

The researchers used data from three Earth-observing satellites in the study: a National Oceanographic and Atmospheric Administration weather satellite, the SeaWiFS instrument aboard the SeaStar (OrbView-2) satellite, and the U.S.-French TOPEX/Poseidon oceanography satellite. Data from SeaWiFS and TOPEX/Poseidon are provided through NASA’s Office of Earth Science, which is dedicated to studying how natural and human-induced changes affect the Earth’s global environment.

More information about the cholera-tracking project can be found on the Internet at: http://geo.arc.nasa.gov/sge/health/projects/cholera/cholera.html