February 23, 2011
Sonia Shah, author of Crude: The Story of Oil, has written a new essay for Yale: Environment 360 on the relationship between weather patterns and outbreaks of cholera:
“Since cholera first erupted from India’s Ganges delta in 1817, the bacterial pathogen has swept across the globe in no fewer than seven worldwide pandemics, afflicting hundreds of millions of people and killing more than 70 percent of its victims within hours if left untreated. The seventh pandemic — the longest one yet — began in Celebes, Indonesia in 1961, and has spread to more than 50 countries and 7 million people. That pandemic continues to this day, staking its latest beachhead in earthquake-ravaged Haiti, where a cholera epidemic occurred last year after a reported absence of some 100 years.
Historically and in the modern popular imagination, cholera has been considered a disease of filth carried in sewage. And yet, over the past decade, research on cholera’s natural habitat and links to the climate have revealed a revolutionary new understanding of the disease as one shaped just as much by environment, hydrology, and weather patterns as by poor sanitation. And as temperatures continue to rise this century, cholera outbreaks may become increasingly common, with the bacteria growing more rapidly in warmer waters.
The University of Maryland cholera expert Rita Colwell, a former director of the National Science Foundation, pioneered the study of Vibrio cholerae, the bacteria that causes cholera, in the environment. She and others have discovered the bacteria in water bodies untouched by human waste, its abundance and distribution fluctuating not with levels of contamination, but with sea surface temperature, ocean currents, and weather changes. After several centuries during which cholera’s spread has been attributed solely to human activity, it has been paradigm-shifting research. “Thirty years ago, we were ridiculed to even say that the bacterium existed in the environment,” Colwell says. “But now it is in textbooks. The evidence is so overwhelming, it is understood.”
While cholera epidemics are caused by multiple factors, of which environmental influences are just one, Colwell and other experts are closely monitoring the potential impact of global warming on the diarrheal disease. “Although there is no clear understanding of the exact nature of the relationship between cholera and climate,” says Tufts University cholera expert Shafiqul Islam, “if climate change leads to more extremes, it will have an impact on cholera.” In fact, it may already have. Over the past 30 years, El Nino events in the Bay of Bengal — characterized, in part, by warmer sea surface temperatures — have increased, paralleling a rise in cholera cases in Bangladesh. The World Health Organization calls it “one of the first pieces of evidence that warming trends are affecting human infectious diseases.”
The growing understanding of the role that climate plays in cholera outbreaks has sparked disagreement between environmental scientists, such as Colwell, and the medical community. While many cholera researchers concur that these environment influences play an important role in the incidence of cholera, especially in places such as Bangladesh and India, most hail from medical fields, which continue to emphasize the role of human activity in the spread of the disease. Scientists such as Matthew Waldor, an infectious disease expert from Harvard University, worry that characterizing cholera outbreaks as a result of environmental influences undermines efforts to prevent the disease using vaccines and other methods.
“There is an inevitability to the environmentalist arguments about cholera,” he says. “If cholera travels by the environment… then it is not preventable.” Whereas linking cholera outbreaks to human activity, he says, reinforces the indisputable — and uncontested — truth that preventing cholera requires changing human activity.”
Read the rest of the article here.