Lecture links cholera to environment
Henry Gens | Thursday, March 20, 2014
As part of the Notre Dame Forum on Women in Leadership, Dr. Rita Colwell, distinguished university professor at the Johns Hopkins University Bloomberg School of Public Health, gave a lecture titled “Oceans, Climate and Human Health: the Cholera Paradigm.”
Colwell prefaced her talk on cholera by borrowing Hippocrates view, which stated that in order to understand medicine, one must understand the seasons of the year.
Cholera is often referred to as pandemic, but it is actually a very local disease in terms of how it arises, Colwell said. The cholera bacteria is found in aquatic systems — from rivers to oceans — the world over, although she said a deep understanding of the bacteria’s habitat was not present until work done by her lab in the 1970s.
“In fact, it was considered 150 years ago that miasma — bad air — was the cause of disease,” Colwell said. “This is before we understood that bacteria and viruses actually cause disease.
“And so you talked about miasma. Washington D.C. was rife with yellow fever, typhoid fever, malaria, cholera, until 1900. In fact, it was known as a miasma swamp.”
Unlike many other pathogens, the cholera bacteria is intrinsically linked to environmental processes, Colwell said.
“Not only does it have the ability to cause disease when ingested in large numbers by humans, but it has a role in the environment,” she said. “Ten percent of strains we’ve tested are luminescent, many of them fix nitrogen, they play a role in the carbon cycle — so they have a very important role to play.
“We know that it’s unlikely that we can eradicate cholera because it’s part of the natural environment. But you can prevent cholera by providing safe drinking water.”
Colwell found over the course of her research in places like India, Bangladesh and Haiti that the above-average temperatures and rainfall combined with poor water systems and large social events, such as religious festivals, significantly contribute to outbreaks of cholera.
This has particular implications for climate change, Colwell said. During the past few decades, she said her team has demonstrated that as sea surface temperatures have risen, so have cholera bacteria populations in those regions.
Highlighting the span and diversity of her research, Colwell also talked about DNA profiling of individuals to construct microbiomes, or genomes of bacteria and other microbes that live inside humans, of different regional populations.
She said her team found a huge discrepancy between healthy Indian and healthy western microbiomes, with the Indian samples having a much larger percentage of pathogens despite the comparable well-being of the individuals from which the samples were taken.
When certain bacteria are present along with cholera bacteria, Colwell said they actually produce more toxins. Hence, there are insidious implications for individuals that contain a mixture of seemingly innocuous bacteria in their microbiome.
Colwell said her lab also investigated different methods and paradigms of providing safe drinking water for communities in a cost-feasible manner. One method targeted copepods, a small crustacean about 300 micrometers in size, which carries the cholera bacteria.
“So if we could eliminate the copepods and the debris from the water, we should be able to reduce cholera,” she said. “So we did the experiments in the laboratory, we tried all kinds of really inexpensive stuff — sari cloth that the women wear, men’s t-shirts that they would wear in Bangladesh — and we found that if we folded used sari cloth about 4 or 5 times, you could get a 20 micrometer mesh filter and that would trap all the particulates and the copepods and all of the other little critters. And you could reduce the numbers of cholera bacteria by 99 percent.”
When Colwell applied for a grant from the National Institutes of Health she was initially rejected because they did not believe men would drink water filtered from a sari — even though, as Colwell found, they were already using sari cloth to filter flies from their beer.
“So young scientists and young discoverers, when you get that rejection, don’t go in a corner and cry; just read it, revise it and resubmit it,” Colwell said.
In the end, Colwell’s team was able to get funding from the National Institute of Nursing for the study and found that villages taught to use the inexpensive sari cloth filter reduced cholera incidence by 50 percent from control.
She said this method worked better than the plastic mesh filter costing a month’s salary, which was provided to members of other villages. A follow-up five years later found that 75 percent of women were still using the cloth method, and former control villages could not be used as a comparison because they had heard about the technique and began using it as well, Colwell said.
“I really like the words of John Muir, founder of the Sierra Club,” Colwell said. “He said ‘when one tugs at a single thing in nature he’ — and I would add ‘she’ — ‘finds it attached to the rest of the universe.’”