A group of researchers has found a connection between ocean temperatures and cholera outbreaks, and plans to test the model worldwide for predicting the incidence of the deadly water-borne disease.
Using data from three ocean-monitoring satellites, the scientists found that increased sea-surface temperatures correlated with cholera outbreaks in Calcutta. Higher temperatures make the coastal waters "bloom" with plankton that carries the deadly cholera bacteria.
Now the plan is to merge ocean temperature forecasts with proven public health measures for reducing the incidence of cholera -- such as instructing residents who drink hazardous water to filter it first through layers of cloth.
"With a combination of these two, we will be probably able to intervene to protect people from a large epidemic," said Anwar Huq of the University of Maryland Biotechnology Institute. "There will still be some cases but we can avert an epidemic.
Huq worked with Rita Colwell, director of the National Science Foundation, and others on the research, recently published as a paper in PNAS (Proceedings of the National Academy of Sciences).
"These experiments fulfill our hypothesis that cholera is associated with environmental conditions," Rita Colwell, director of the National Science Foundation, said in a prepared statement. She is presently on leave from the University of Maryland Biotechnology Institute.
Cholera is a bacterial infection that affects mainly the small intestine and can be fatal. In 1993, a total of 296,206 new cases were reported in South America. Most cholera outbreaks start in coastal areas.
Huq, Colwell and their colleagues studied satellite data and 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 of plankton and the cholera outbreaks.
The group correlated years of hospital cholera records from Bangladesh with sea temperature and ocean height data that came from a variety of satellites and sea-surface observations.
The satellites, including the U.S.- French TOPEX/Poseidon oceanography satellite, measured water temperature and ocean height, as well as colors that indicated plankton growth.
Scientists believe that sea height also affects cholera outbreaks because tides reach further inland to affect more people who drink or bathe in brackish water carrying cholera.
"Bangladesh is very low and flat," said co-author Louisa Beck of California State University at Monterey Bay and a resident scientist at Ames, "and tidal effects are felt almost halfway up into the country."
Scientists have used similar approaches with satellite data to study malaria, Lyme disease and Rift Valley fever.
If the model that worked in Bangladesh could be extended globally, it could serve as an early warning system, said Brad Lobitz, a scientist at the NASA Ames Research Center, and the lead researcher on the project.
Once alerted to rising temperatures in coastal waters, public-health officials could issue warnings to prevent or respond to the spread of cholera, such as instructing and reminding people about cloth filters, Huq said.
"When four folds of a sari are used as a filter, 99 percent of the attached bacteria onto plankton and particles are removed," Huq said. Huq has demonstrated the method with women in the area where data were collected for the study.
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