Deadly cholera outbreaks could increase with climate change

A view shows people wading through a flooded street in Srinagar September 15, 2014. Indian emergency workers on Monday battled to prevent waterborne diseases like cholera from spreading as fetid water swilled around the Kashmir valley more than a week after the worst flooding in more than a century. REUTERS/Danish Ismail

Increasingly severe heat waves and more frequent and intense flooding due to climate change will spur the spread of cholera in vulnerable regions of the world, new research suggests.

In an effort to better understand the environmental conditions that cause deadly cholera outbreaks and to be able to predict them in the future, researchers based at the University of Maryland compiled more than 40 years of cholera studies to compare weather and groundwater conditions to patterns of outbreaks.

Based on their findings, the scientists have successfully developed a method of using satellite data to anticipate cholera outbreaks two to four months in advance, the team reported yesterday (Dec. 15) here at the 47th annual meeting of the American Geophysical Union (AGU) in San Francisco. [7 Devastating Infectious Diseases]

"This is a paradigm shift in our interpretation of cholera epidemiological data," study co-author Rita Colwell, a researcher at the University of Maryland, College Park, told reporters during a news briefing. "For the first time, hydrological and climatological data are being incorporated in our understanding of the outbreaks."

Cholera is a bacterial disease caused by a single-celled organism called Vibrio cholerae that thrives in aquatic environments. When ingested in high concentrations, the bacterium can infect a person's small intestine, causing vomiting, fever and excessive diarrhea that can result in lethal dehydration.

Modern sanitation has eliminated cholera in most developed countries, but regions of the world with poor water sanitation and crowded living conditions are still largely vulnerable, including many parts of Haiti, Pakistan and coastal Africa. An estimated 3 million to 5 million cholera cases, and 100,000 to 120,000 deaths, occurred worldwide in 2013, according to the World Health Organization (WHO).

The researchers found that both unusually high air temperatures and periods of excessive rainfall create environmental conditions that favor bacterial growth. In dry conditions, river levels decrease, and bacteria accumulate in dangerously high concentrations. During excessive rainfall, flooding can spread bacteria to regions that haven't previously been infected, resulting in fast-spreading epidemics.

Given that both extreme heat and more intense storms are expected to increase due to climate change, the researchers anticipate that cholera outbreaks could become more frequent in the future, Colwell said. Even in the past decade, regions of Africa have seen a re-emergence of the disease due to extreme weather, the team reported.

The researchers are now analyzing data from NASA's Gravity Recovery and Climate Experiment (GRACE) satellites to identify elements of the climatological and hydrological cycles including temperature, precipitation and groundwater levels that correlate with cholera outbreaks, and will use the information to predict future outbreaks months in advance.

These predictions are possible because weather patterns that occur up to six months before a given drought or monsoon season impact groundwater conditions six months later, said study co-author Ali Akanda, a researcher at the University of Rhode Island.

"Large rivers are variable interannually," Akanda told Live Science. "So, depending on how a particular monsoon season is going, it will have an impact on the upcoming dry season, and similarly, the dry seasons have an impact on monsoons."

The researchers hope their ability to predict cholera outbreaks will improve as the quality of satellite data becomes more accurate in the future. In their follow-up research, the researchers hope to explore the role that humans play in transferring the disease from region to region, Colwell told Live Science.

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