With the threat of a warmer, wetter world and a larger global population, scientists are researching how climate change may impact the spread of infectious diseases, such as cholera and dengue fever, and how outbreaks may be prevented. "Changing Planet" is produced in partnership with the National Science Foundation.
ANNE THOMPSON, reporting:
From Swine Flu to Spanish Flu, the Black Death to biblical plagues, infectious diseases have tormented the world since the beginning of recorded history. Today, as temperatures around the world get warmer, bringing more storms and flooding, and the global population increases, infectious disease may become an even bigger problem.
Dr. Rita Colwell at the University of Maryland studies a disease that claims over 100,000 lives a year: Cholera.
Dr. RITA COLWELL (Microbiologist, University of Maryland): The disease is manifested by severe vomiting, diarrhea and extensive loss of fluid. And if not replenished, death will ensue from systemic shock.
THOMPSON: Cholera is caused by a bacterium called Vibrio cholerae that thrives in coastal waters, rivers, and estuaries around the globe. It is often transmitted to humans through contaminated food or water.
COLWELL: The disease occurs really in places where there is no access to safe drinking water or sanitary conditions, in countries like Haiti, in Bangladesh, or countries where there is not, for a given period of time, access to safe water.
THOMPSON: Developed countries like the U.S. take great care in filtering their drinking water. But in lesser-developed areas, a river or stream may be a community's only source of water, where cholera can be easily spread.
COLWELL: In a country like Cambodia or Bangladesh, where less than twenty percent of the people, maybe even ten percent, have access to safe drinking water, the mortality for children under the age of five can be as high as two hundred will die out of every thousand born.
THOMPSON: Colwell fears that climate change may create the right conditions for cholera to spread, by causing warmer water temperatures, flooding, and even increased effects from El Nino, the weather phenomenon that periodically disrupts regional climate patterns.
COLWELL: If we have warming so that we have longer springs that run into a longer fall, then the time of year in which the disease can occur will be much lengthened.
THOMPSON: Changes in climate may also increase other diseases carried by such hosts as fleas, rats, ticks, and mosquitoes.
Dr. ANDY MONAGHAN (Atmospheric Scientist, NCAR): We're specifically looking at one particular mosquito called Aedes aegypti. It's a unique mosquito in that it's kind of a city slicker mosquito rather than a more rural mosquito.
THOMPSON: Dr. Andy Monaghan is an atmospheric scientist at the National Center for Atmospheric Research, or NCAR. He is part of a team of scientists from NCAR, the Centers for Disease Control, and universities in the United States and Mexico that is working to uncover the mysteries of a disease spread by mosquitoes: Dengue fever.
Dr. MARY HAYDEN (Medical Anthropologist, NCAR): It's commonly referred to as break-bone fever, because when people come down with this illness, it feels as if every bone in their body is breaking.
THOMPSON: Worldwide, anywhere between 50 and 100 million people are infected with dengue each year. Its most extreme form can lead to a hemorrhagic fever.
HAYDEN: Often times we see bleeding. So you could see bleeding from the eyes, bleeding from the nose, different types of-- of bleeding.
THOMPSON: Scientists believe climate change may increase the likelihood of wetter environments, making it easier for mosquitoes to breed, since they lay their eggs just above the surface of calm, stagnant water, like swamps or inside old tires.
MONAGHAN: When it rains, the water levels rise. And as soon as those eggs become submerged in water, they’ll hatch.
THOMPSON: While the U.S. has been able to escape outbreaks in recent times, scientists warn that these diseases lurk nearby, even in our backyard.
HAYDEN: In south Texas we have documentation of dengue from '80 on. In the twenties and thirties, we saw a lot of-- of dengue fever in the southern United States. And we actually have documentation from 1780 of an outbreak of dengue fever in Philadelphia.
THOMPSON: Scientists around the world are working hard to solve the questions of climate change and prevent the spread of diseases like cholera and dengue fever. But whether by bugs or bad water, the threat of outbreaks of infectious diseases will continue to keep us on the alert.
A surprising factor may be contributing to the spread of malaria in Malaysia, new research has found. In a new study, published Friday in the journal Emerging Infectious Diseases, scientists argue that deforestation is causing environmental changes that have upped transmission of a form of the infectious disease usually found only in monkeys.
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