Scientists say filtering water through old sari fabric might be enough to reduce cholera cases by about half in rural villages in Bangladesh.
In a study appearing this week in the Proceedings of the National Academy of Sciences, scientists filtered pond and river water through nylon mesh and through old, much-washed sari cloth. They concluded that the sari solution worked best and could save lives in villages where the waterborne disease annually sickens thousands of people.
"Sari cloth is cheaper and we found that it is much more effective than the nylon mesh," said Rita R. Colwell, a professor of microbiology at the University of Maryland, College Park, and primary author of the study.
Colwell said researchers discovered in laboratory studies that most of the cholera bacteria in ponds, rivers and other standing water is attached to or in the gut of a copepod, a type of zooplankton commonly found in standing water.
When people drink unfiltered water, she said, they swallow the copepods and introduce cholera bacteria into their system. The germ grows in the human gut, releasing a toxin that causes extreme diarrhea and cramping.
Filtering the copepod out of drinking water reduced the rate of cholera by at least half, Colwell said. There also was some evidence that other types of germs were removed because women in the villages with sari-filtered water reported fewer incidences of diarrhea and other digestive problems, she said.
In modern hospitals, cholera is easily controlled, but the untreated disease kills 50 percent to 80 percent of those infected. It is most lethal for children under 5 and for the elderly.
Colwell said the rural Bangladesh villages are many hours of hard travel away from good medical care and finding a simple way to combat cholera could have a major impact on the lives of people there.
Dr. John Mekalanos, a cholera expert and professor at the Harvard Medical School, said, "Anytime you can reduce a life-threatening disease by (50 percent) with something this simple it could make a big difference in the region and elsewhere in the world."
There were 184,000 cases of cholera reported from 58 countries in 2001, according to the World Health Organization. More than 2,700 people died. However, Bangladesh was not included in these statistics, said Colwell, and it is thought the cholera rate and the number of deaths from the disease are very high. Mekalanos estimated that there are a million cases of cholera in Bangladesh annually and thousands of unreported deaths.
In the study, Colwell and her colleagues selected 65 villages where cholera was a major threat. In 27 of the villages, women were instructed to use bits of sari cloth, folded eight times, as a filter when they captured household water from ponds, lakes or rivers. Twenty-five villages used the nylon filters, and 13 villages received no filtering instructions and continued to gather water in the traditional way. There were about 44,000 people in each part of the study.
After 18 months, the rate of cholera in villages using the sari filters was about .65 cases per 1,000 people per year. The rate was about .79 cases in the villages using nylon filters, and about 1.16 cases per 1,000 people in the control villages.
Colwell said the researchers found that the majority of those who got sick in the sari-filtered villages had visited villages where they drank unfiltered water.
She said the rate of cholera was extremely low among people who drank only the sari-filtered water.
"We found in the laboratory that we could remove more than 99 percent of the bacteria with the sari cloth," said Colwell.
A sari, the garment favored by most Hindu women, is made of lightweight, gauzelike cotton fabric.
Colwell said experiments showed that old sari cloth filtered better than new cloth. As the sari is washed repeatedly, she said, the spaces between threads in the cloth mesh narrow and trap finer particles.
"We tried other material, but the sari was by far the most effective," said Colwell. And it is available in most Bangladesh households. "Every woman there wears a sari," she said.
By Paul Recer