Rita Colwell: satellite early-warning, plankton link and simple cloth filtration cut cholera in Bangladesh

Rita Colwell, former director of the National Science Foundation and a microbiologist who has led long-term cholera studies, told attendees at a presidential lecture series that cholera is closely tied to environmental conditions and can be predicted months in advance by satellite measurements of sea-surface temperature, chlorophyll and sea-surface height.

Colwell said the bacterium that causes cholera, Vibrio cholerae, lives year-round in coastal and estuarine waters and attaches to small crustacean plankton called copepods. She described a predictive model that combines satellite data with ground measurements and historical hospital records in Bangladesh to forecast cholera peaks in the spring and fall. "We were able to predict months in advance," Colwell said, noting a test where the team estimated about 24 cases per thousand and later received ground counts of 25 to 26.

The model, Colwell said, links a chain of seasonal events: increased sunlight and warming of surface waters, a phytoplankton bloom followed by a zooplankton (copepod) bloom, and a sharp rise in vibrios on plankton surfaces. She told the audience each copepod can carry "10,000 to a hundred thousand individual Vibrio cholerae cells," and that a dose of roughly one million organisms per teaspoon of water can cause severe illness. Colwell emphasized that most infections are mild or asymptomatic — she cited figures from her talk that about 75 percent are asymptomatic, 18 percent mild, 5 percent moderate and about 2 percent become severely ill and require hospitalization.

Colwell described parallel findings in Peru, parts of Africa and Mexico, and said El Niño and other large-scale climate anomalies have produced measurable changes in sea-surface conditions that preceded major epidemics. She and collaborators used satellites (NASA data) plus 10–15 years of ground sampling in Matlab and other sites near Dhaka to build and validate their predictive model.

On interventions, Colwell described a low-cost, locally appropriate filtration test and field trial. Laboratory work showed folded cloth removed about 99 percent of bacteria attached to plankton-sized particulates. In a three-year study in Bangladesh funded through the National Institutes of Health (the study was administered by the nursing institute, Colwell said), households instructed to filter drinking water through folded sari or terry cloth saw roughly a 50 percent reduction in cholera cases compared with controls. "We were able to reduce cholera by 50 percent, by this very simple technique," she said, adding that compliance remained 60 to 70 percent in follow-up surveys four years after the trial ended.

Colwell also discussed genomic work: teams have sequenced multiple V. cholerae strains from patients and the environment to trace geographic patterns and evolutionary changes. She said the group has sequenced about 15 clinical isolates and another ~10 environmental strains so far and plans substantially larger sequencing efforts to map strain differences across regions.

During audience questions she addressed sanitation and practical barriers: much of the cholera burden occurs in remote villages that lack piped water and sewage, where households draw water from ponds and rivers; chlorination and boiling are often impractical (boiling is limited by fuel availability), and deep wells introduced by development financing have in some cases produced arsenic exposure. Colwell described low-tech options underway with engineers (sand/charcoal/gravel filters with an iron component for about $10) and emphasized that simple, durable solutions that can be maintained locally are most useful for poor, flood-prone regions.

Colwell framed the work as a paradigm for other environment-linked infectious diseases (West Nile, dengue, malaria) and said climate-driven changes in ocean and inland water conditions can alter disease patterns. She closed by urging international scientific collaboration across molecular biology, field epidemiology and satellite remote sensing and said, "We as humans are but one species in a very intricate pattern of biological life on this planet," adding that protecting the planet is essential because "it is the only one we have."