NSF Director Colwell Fights Spread of Cholera with Saris
Women in a small village in Bangladesh are fighting the spread of the diarrheal disease cholera by filtering water through the same type of cloth with which they make their brightly hued saris. The simple filtration method seems to dramatically reduce the bacteria in the water, said Rita Colwell, director of the National Science Foundation, at a lecture at HSPH on April 24. The Department of Population and International Health sponsored the lecture.
"The solution to controlling cholera," said Colwell, "will be high-tech analyses to produce extremely low-tech solutions."
Colwell
and her colleagues taught the women the filtration method two years ago.
Every morning, she said, the women walk to the river that runs by their
village and collect water that they will later drink. The same river serves
as a toilet, bath, and sink, creating an environment in which diseases
can easily grow.
Colwell teaches the women to fold the sari cloth into eight layers and place the cloth over an empty vessel into which the dirty water is poured. The cloth captures the bacteria in its fine weave, which results in drinking water that is visibly cleaner.
The number of times the sari cloth is folded seems to matter. Colwell has conducted 10 trials in different locations to compare the results of filtering water through cloth that had been folded four or eight times; the eight-folded cloth seems to serve as a better filter.
The sari cloth is easily cleaned by rinsing and drying in the heat of the sun.
Sociologists working with Colwell warned her that the undereducated women would not understand what she was trying to teach them. "They got it," said Colwell. She knew the lesson had been learned after a filmographer taping the women for a television show asked one to drink unfiltered water for the purposes of the segment. The woman refused.
Cholera infections can result in severe diarrhea and dehydration. Only seven percent of victims end up hospitalized, said Colwell, but about 75 percent of people infected don't show symptoms. Fatalities are rare in countries with adequate treatment facilities, but mortality rates are as high as 50 percent in areas with inadequate medical treatment, according to the Centers for Disease Control and Prevention (CDC).
HSPH researcher Richard Cash played a key role in developing inexpensive treatment methods for cholera. In 1968, he and a colleague conducted the first clinical trial to show that drinking a saltwater-glucose solution after infection greatly reduced risk of death because that helped replace lost fluids.
The disease is caused by the bacterium V. cholerae that attaches itself to tiny, water-borne animals called copepods. The bacteria collect around the mouths and on the egg casings of female copepods, said Colwell, and the bacteria and copepods seem to have developed a mutually beneficial relationship. The animals offer transportation to the bacteria, which in turn help rupture the egg casings of the females so that they can disperse their ova.
The copepods feed on plants called phytoplankton, which bloom when water temperatures rise. Recognizing the importance of water temperature proved to be critical in understanding the cycle of cholera. Until the 1980s, researchers who were unable to detect V. cholerae in water assumed that the bacteria had died, but Colwell and her colleagues--using new, more precise techniques--found the bacteria actually survived in an inactive, non-culturable stage when water got colder. The discovery helped explain the reemergence of cholera in waters that had been tested and found free of the bacteria. The work was not taken seriously at first.
"I remember CDC officials referring to the non-culturable forms of the bacteria as 'Colwell's ghosts'," she said.
Colwell and her colleagues began tracking climate changes with satellites and correlating the data to cholera outbreaks. They found that water temperatures and sea levels could help predict cholera incidents. The outbreaks seem linked to seasonal changes in the spring and fall when water warms and winds increase.
"The environmental aspects of cholera outbreaks have never been taken seriously," said Colwell. She is continuing to analyze the data collected from satellites and inexpensive filtration methods such as the saris.
"We assumed wrongfully in the past few years that infectious diseases
had been conquered," she said.
