Warming Trend: How Climate Shapes Vibrio Ecology
Warming Trend: How Climate Shapes Vibrio Ecology
In coastal Bangladesh, cholera is familiar, and so is its remedy: drinking a solution of rehydration salts. "Once you have cholera," says Islam, "you need to hydrate yourself for a few days. … In a few days, the cholera will get flushed out of your system, and you're safe. If you don't rehydrate, you may die."
But when an epidemic strikes an unprepared region, the death toll can be very high. The ongoing cholera epidemic that first struck Haiti in the aftermath of a devastating 2010 earthquake has had a mortality rate of more than 6% as compared with 0.01% during a predictable spring or fall outbreak in Bangladesh, where cholera deaths have dropped dramatically in recent decades despite rising infection rates. Recent epidemics in Zimbabwe, Angola, Nigeria, and Sudan all caused death rates above 3%.
Predictable endemic cholera is a phenomenon of tropical coasts. In contrast, places that suffer massive epidemics at unexpected times are often inland, away from major river deltas. To gather clues to the environmental factors involved in cholera in these epidemic regions, Colwell and Antarpreet Jutla of West Virginia University studied historical data on air temperature, rainfall, and cholera outbreaks in India's Indus River Basin from 1875 to 1900. They found that epidemics were strongly predicted by a particular weather pattern: an unusually hot summer followed by heavy rainfall in the fall. High temperatures favor the growth of V. cholerae in local waters that spread across the landscape during flooding.
(Enlarge Image)
(Enlarge Image)
"The historical pattern from the Indus River Basin holds up in other places," notes Jutla. Increased numbers of cholera outbreaks following heavy rainfall have been recorded in Haiti and Africa. A comparison of two major flood events in Pakistan points up the powerful influence of weather. A disastrous earthquake in 2005 did not bring a significant outbreak of cholera, because it happened high in the mountains, where cold temperatures discouraged the growth of V. cholerae. But in the hot August of 2010, when a flood struck Pakistan's lowlands, 600,000 people sought treatment for diarrheal diseases, including cholera.
In Haiti, the strain of V. cholerae that caused the post-earthquake epidemic is reported to have been introduced by Nepalese United Nations peacekeepers who came to help with disaster relief. Colwell points out, however, that the epidemic was also preceded by a perfect storm of environmental conditions. V. cholerae thrives in alkaline waters, and Colwell hypothesizes that the earthquake may have battered the island's limestone foundation, releasing ground-up rock into the rivers and increasing the pH. An intensely hot summer was then followed by the greatest rainfall in 50 years. Drinking water and sanitation systems were devastated by the earthquake. In Colwell's view, cholera emerged in Haiti because of a complex array of environmental conditions—it was not a simple case of the disease being carried from one part of the world to another inside a human gut.
(Enlarge Image)
Preparing for the Unexpected
In coastal Bangladesh, cholera is familiar, and so is its remedy: drinking a solution of rehydration salts. "Once you have cholera," says Islam, "you need to hydrate yourself for a few days. … In a few days, the cholera will get flushed out of your system, and you're safe. If you don't rehydrate, you may die."
But when an epidemic strikes an unprepared region, the death toll can be very high. The ongoing cholera epidemic that first struck Haiti in the aftermath of a devastating 2010 earthquake has had a mortality rate of more than 6% as compared with 0.01% during a predictable spring or fall outbreak in Bangladesh, where cholera deaths have dropped dramatically in recent decades despite rising infection rates. Recent epidemics in Zimbabwe, Angola, Nigeria, and Sudan all caused death rates above 3%.
Predictable endemic cholera is a phenomenon of tropical coasts. In contrast, places that suffer massive epidemics at unexpected times are often inland, away from major river deltas. To gather clues to the environmental factors involved in cholera in these epidemic regions, Colwell and Antarpreet Jutla of West Virginia University studied historical data on air temperature, rainfall, and cholera outbreaks in India's Indus River Basin from 1875 to 1900. They found that epidemics were strongly predicted by a particular weather pattern: an unusually hot summer followed by heavy rainfall in the fall. High temperatures favor the growth of V. cholerae in local waters that spread across the landscape during flooding.
(Enlarge Image)
(Enlarge Image)
"The historical pattern from the Indus River Basin holds up in other places," notes Jutla. Increased numbers of cholera outbreaks following heavy rainfall have been recorded in Haiti and Africa. A comparison of two major flood events in Pakistan points up the powerful influence of weather. A disastrous earthquake in 2005 did not bring a significant outbreak of cholera, because it happened high in the mountains, where cold temperatures discouraged the growth of V. cholerae. But in the hot August of 2010, when a flood struck Pakistan's lowlands, 600,000 people sought treatment for diarrheal diseases, including cholera.
In Haiti, the strain of V. cholerae that caused the post-earthquake epidemic is reported to have been introduced by Nepalese United Nations peacekeepers who came to help with disaster relief. Colwell points out, however, that the epidemic was also preceded by a perfect storm of environmental conditions. V. cholerae thrives in alkaline waters, and Colwell hypothesizes that the earthquake may have battered the island's limestone foundation, releasing ground-up rock into the rivers and increasing the pH. An intensely hot summer was then followed by the greatest rainfall in 50 years. Drinking water and sanitation systems were devastated by the earthquake. In Colwell's view, cholera emerged in Haiti because of a complex array of environmental conditions—it was not a simple case of the disease being carried from one part of the world to another inside a human gut.
(Enlarge Image)
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