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 ASA is providing new insights from space that may
help health officials predict outbreaks of deadly waterborne
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, sea height and other climate
variables. The work is described in a recent paper coauthored
by 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, founder
and former president of UMBI, and now Director of the National
Science Foundation. She is presently on leave of absence from
the University of Maryland, and is coauthor of the cholera-tracking
project paper.
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," according to Brad Lobitz, principal author of
the paper and a contract scientist at NASA's Ames Research Center,
located in California's Silicon Valley. 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
not only can measure water temperature and ocean height, but
also 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 half way up into the country," said coauthor
Louisa Beck of California State University at Monterey Bay and
a resident scientist at Ames.
"The
1992-to-1995 study is important because all the remote sensing
satellite data are in the public domain," Beck said. "The
main point is that 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. The 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. More information
about the cholera-tracking project is on the Internet at: http://geo.arc.nasa.gov/sge/health/projects/cholera/cholera.html
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 US-French TOPEX/Poseidon oceanography satellite.
Data from SeaWiFS and TOPEX/Poseidon are provided through NASA's
Office of Earth Sciences, which is dedicated to studying how
natural and human-induced changes affect the Earth's global environment.
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